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DIY Stompboxes => Building your own stompbox => Topic started by: Killthepopular on August 02, 2019, 11:43:10 AM

Title: Low Gain, neutral dist/OD
Post by: Killthepopular on August 02, 2019, 11:43:10 AM
I'm looking for an easy, low gain dist or OD. It will be like an amp emulator, just a flat, neutral sounding OD that can go from clean to gritty with the gain knob. Tubeyness would be a plus but I'm not fussed about that, I just want to add a little dirt without changing the tone. I'm gonna try ROG Eighteen (fets), Crowther Hotcake (opamp clipping) and DOD 250 (opamp clipped by silicon diodes). I'm gonna breadboard these. I'm sticking to designs with only a few components to make things easy. These 3 circuits each require between 20-30 components, so pretty simple.
Are these circuits reasonably low gain? I know the DOD will be fine (especially with LEDs) and the Crowther is known for being good for low gain but I'm not sure about the eighteen...

(https://i.postimg.cc/Lnx9H8Y0/2duxshd.gif) (https://postimg.cc/Lnx9H8Y0)

(https://i.postimg.cc/mzWRdcJh/DOD-250-Overdrive-Schematic.png) (https://postimg.cc/mzWRdcJh)

(https://i.postimg.cc/KKMxr79d/eighteen.png) (https://postimg.cc/KKMxr79d)

I was considering a Rat but I don't want to go mid-focussed and I already have an SD-1 for that. I'm considering an OCD too though that has slightly more components (35) and also it doesn't seem to be very low gain; I want to go from totally clean to slightly gritty ideally.
Any suggestions?
Title: Re: Low Gain, neutral dist/OD
Post by: iainpunk on August 02, 2019, 01:02:08 PM

(https://i.postimg.cc/8fQFCZ2c/embryo-green.png) (https://postimg.cc/8fQFCZ2c)
 this seems to be quite clean when turned down, but gets crisp and warm when pushed

the transistors are BF245 and the diodes are 1n4148
Title: Re: Low Gain, neutral dist/OD
Post by: Killthepopular on August 02, 2019, 01:22:28 PM

(https://i.postimg.cc/8fQFCZ2c/embryo-green.png) (https://postimg.cc/8fQFCZ2c)
 this seems to be quite clean when turned down, but gets crisp and warm when pushed

Is it some sort of low gain fuzz?
Title: Re: Low Gain, neutral dist/OD
Post by: Killthepopular on August 02, 2019, 01:23:11 PM
Actually I think I'll skip the ROG Eighteen, seems like it's not really intended for low gain.
Title: Re: Low Gain, neutral dist/OD
Post by: GGBB on August 02, 2019, 02:45:12 PM
Pretty much anything that has a variable gain or drive control could be set at low gain. You could even modify the control so that it will only give low gain. It sounds like what you are really after is a pedal that does nice nuetral tubey low gain sounds.  A couple of those that I'm aware of would be the Peppermill and the Timmy. Maybe the Klon as well. I also like Bluesbreakers, but those need tweaking to get to nuetral territory.
Title: Re: Low Gain, neutral dist/OD
Post by: Mark Hammer on August 02, 2019, 04:13:16 PM
This thing seems to make a lot of people happy:  https://www.diystompboxes.com/smfforum/index.php?topic=107216.0  It can dial in softer clipping, and offers a lot of flexibility in terms of tone shaping.  Aims for low to mid-gain territory, and doesn't use many parts.
Title: Re: Low Gain, neutral dist/OD
Post by: Killthepopular on August 02, 2019, 05:07:11 PM
Pretty much anything that has a variable gain or drive control could be set at low gain.

So, what, I could say, take an OCD for example and just change one pot or one resistor to reduce the gain of the first boost stage in the pedal and that would give me a lower gain circuit?

It sounds like what you are really after is a pedal that does nice nuetral tubey low gain sounds.  A couple of those that I'm aware of would be the Peppermill and the Timmy. Maybe the Klon as well. I also like Bluesbreakers, but those need tweaking to get to nuetral territory.

Would you recommend the peppermill? I thought it looked promising but the demo clips sounded so terrible to me that i thought it wouldn't be worth bothering with.
I wasn't going to bother with the timmy, I had just assumed it would be a fairly complex circuit but now I see it has a modest 31 components. Maybe I'll give it a go. I know it's like possibly the most widely recommended dirt pedal these days.
Klons sound good to me but it uses maybe twice as many components as these other circuits so I'll skip it I think (this is my first attempt at breadboarding a complete pedal).
Tempted by the bluesbreaker...
Title: Re: Low Gain, neutral dist/OD
Post by: Killthepopular on August 02, 2019, 05:16:20 PM
Oh yeah, I should probably specify that this will be an amp-like pedal in terms of how I want to use it. It will be like Pedal->clean amp or pedal->cab sim. So ideally it should be something that sounds ok on its own as opposed to one of those pedals where it's like "oh you should NEVER use it into a clean amp!!"
Title: Re: Low Gain, neutral dist/OD
Post by: ElectricDruid on August 02, 2019, 05:25:16 PM
DOD 250 is fairly hard, "distortion" more than "overdrive" I'd say. Things with the clipping diodes after the gain stage tend to be a bit harder in my experience. But you can back it off, obviously.

I was going to suggest a Tubescreamer since that does nice overdrive sounds and is simple enough circuit, but the tone-shaping is probably not anything you could call neutral. Still, you could leave a few bits out!
Title: Re: Low Gain, neutral dist/OD
Post by: Steben on August 02, 2019, 07:19:17 PM
Low gain blues driver?
Title: Re: Low Gain, neutral dist/OD
Post by: roseblood11 on August 02, 2019, 07:51:12 PM
Mad Professor Sweet Honey Overdrive!!!
Or maybe Black Cat OD-1 with OP275 opamp
Title: Re: Low Gain, neutral dist/OD
Post by: GGBB on August 02, 2019, 10:41:58 PM
So, what, I could say, take an OCD for example and just change one pot or one resistor to reduce the gain of the first boost stage in the pedal and that would give me a lower gain circuit?

More or less - the details of "stages" would differ depending on the pedal, for example in a Bluesbreaker, the gain pot simultaneously controls gain for both stages, so use a smaller pot and you have only the low gain settings. That was my point really - use a smaller gain pot and you essentially are preventing yourself from cranking it up.

Would you recommend the peppermill?

It came to mind because you said low gain. Never built one yet, but I like the clips I've heard - it's different than the usual dual opamp fair a la TS, Timmy, Bluesbreaker, ... and most definitely low gain and neutral. It seems to me in limited experience that not a lot of pedals do very light overdrive particularly well - most are best suited at mild to medium overdrive and some higher. I think - based on clips - the Peppermill does the very light stuff quite nicely for my tastes.

Title: Re: Low Gain, neutral dist/OD
Post by: antonis on August 03, 2019, 03:48:45 AM
Fender Blender without octave configuration.. :icon_wink:
Title: Re: Low Gain, neutral dist/OD
Post by: Fancy Lime on August 03, 2019, 05:34:59 AM
Hi Killthepopular,

what you describe is pretty much exactly Craig Anderton's Tube Sound Fuzz, aka the Way Huge Red Llama. This is based on CMOS inverter clipping, which I find by far the best for the transition region between totally clean ad juuuuust a little overdriven. Very natural and pleasing. Tube-like? Some say yes, some say no, I don't care. It's CMOS overdrive and it sounds like a CMOS overdrive. It's low part count and can be extended to be extremely complicated, if you should which so. Very educational circuit. It's also easy to lower the overall gain range, if you want. Have a look at youtube videos of the Red Llama to get an idea about the sound. find the ones with gain at minimum.

Cheers,
Andy
Title: Re: Low Gain, neutral dist/OD
Post by: bluebunny on August 03, 2019, 10:53:10 AM
I quite like Joe Davisson's EZ-250.  Only 15 parts (+ pots).  Links for: thread (https://www.diystompboxes.com/smfforum/index.php?topic=103671.0), schematic (http://www.bouron.org.uk/marc/ez250.jpg), my layout (http://www.bouron.org.uk/marc/EZ250B.GIF).
Title: Re: Low Gain, neutral dist/OD
Post by: Killthepopular on August 03, 2019, 12:47:51 PM
I was going to suggest a Tubescreamer since that does nice overdrive sounds and is simple enough circuit, but the tone-shaping is probably not anything you could call neutral. Still, you could leave a few bits out!

I like the OD1, but I already have an SD1 which I have modded fairly extensively (mainly to make it more neutral) so I think I have the neutralish tubescreamer territory covered if I'm being honest.
Title: Re: Low Gain, neutral dist/OD
Post by: Fancy Lime on August 03, 2019, 12:50:47 PM
I quite like Joe Davisson's EZ-250.  Only 15 parts (+ pots).  Links for: thread (https://www.diystompboxes.com/smfforum/index.php?topic=103671.0), schematic (http://www.bouron.org.uk/marc/ez250.jpg), my layout (http://www.bouron.org.uk/marc/EZ250B.GIF).

I see your 15 parts + pots and raise you 8 parts + pots. The good ol' Electra distortion: http://fuzzcentral.ssguitar.com/schematics/electradistortion.gif
One of the most simple, yet amazingly good sounding little circuits. You might want to use two series pairs of Ge diodes instead of two singles and add a gain pot up front (wired like in the Jordan Bosstone: http://fuzzcentral.ssguitar.com/schematics/bosstoneschem.gif called "Attack" here). Or, simpler, just add a "softness" pot. See Arons mod tips: https://www.diystompboxes.com/cnews/mods.html #1 and #7, respectively. Still 10 parts or less.

Andy
Title: Re: Low Gain, neutral dist/OD
Post by: Killthepopular on August 03, 2019, 12:52:28 PM
Low gain blues driver?

The blues driver layout i looked at required like over 100 components... Even without the input and output buffers that's a lot. This is pretty much the first time I've breadboarded a dirt pedal so I hope to keep it simple.
Title: Re: Low Gain, neutral dist/OD
Post by: Killthepopular on August 03, 2019, 01:21:50 PM
Mad Professor Sweet Honey Overdrive!!!
Or maybe Black Cat OD-1 with OP275 opamp

Sweet honey is a bit complicated looking. Black cat looks pretty simple but doesn't sound very neutral.
Title: Re: Low Gain, neutral dist/OD
Post by: Killthepopular on August 03, 2019, 01:27:35 PM
what you describe is pretty much exactly Craig Anderton's Tube Sound Fuzz, aka the Way Huge Red Llama. Very natural and pleasing.

Yeah this looks like a really good suggestion. Lowest part count I've found so far, can do clean and  the tones sound good at low and high gain settings. And yeah, I'm no tube connoiseur but it sounds pretty tubey to me.
What's the sonic difference between those two versions of the same circuit?
Title: Re: Low Gain, neutral dist/OD
Post by: Killthepopular on August 03, 2019, 01:37:51 PM
I think What I'm hoping to find is a circuit that I can put in front of any clean pedal platform (clean amp, cab sim) and leave it on all the time, giving a little twist of the gain knob for more grit or zero grit. It doesn't have to be totally transparent, I just don't want it to cut loads of bass like so many dirt pedals seem designed to do. I mostly play on my own so I don't need the whole "cut through the mix" thing. My SD1 and DS1 sound good but they sound a bit thin. My Gypsy fuzz is pretty neutral but struggles to give me low gain (doesn't seem to clean up like fuzz faces do).
I want it to be pretty simple just because I'm a noob and want to try out a couple different circuits without buying loads of obscure parts.
So far the Dod 250 and the Red Llama look closest to what I want.

What about fuzz faces? Are those any good for what I'm looking for? I like their sound.
Title: Re: Low Gain, neutral dist/OD
Post by: Killthepopular on August 03, 2019, 01:39:48 PM
I quite like Joe Davisson's EZ-250.  Only 15 parts (+ pots).  Links for: thread (https://www.diystompboxes.com/smfforum/index.php?topic=103671.0), schematic (http://www.bouron.org.uk/marc/ez250.jpg), my layout (http://www.bouron.org.uk/marc/EZ250B.GIF).

What's the advantage to using transistors instead of an opamp? More "Buttery"? Whatever that means...
Title: Re: Low Gain, neutral dist/OD
Post by: Mark Hammer on August 03, 2019, 01:57:48 PM
A fellow brought over a Catalinbread Hyperpak for me to repair the other day.  It's a close relative of bother the Red Llama and Tube Sound Fuzz.  The drawing doesn't indicate, but the chip is a 4049UB.  As you can probably tell from the second stage feedback resistor, it's a little more intense than a Red Llama.  If it were mine, I'd drop R4 down from 1m.  VERY loud circuit, so you can afford to insert some form of passive tone control between the output and Volume pot.

I made myself an "Amber Alpaca" ( :icon_rolleyes: ), which is essentially a Red Llama/TSF, but with less gain.  The feedback resistor in stage 2 is 680k.  The feedback caps in each stage are 120pf, and the input caps for each stage are 100nf.  I also used a 1k current-limiting resistor for feeding the V+ pin on the chip.  At min gain it sounds very much like clean, but with a hint of coloration, and a little more lower-mids muscle.  Makes amp grind sound nice.

(http://guitar-fx-layouts.42897.x6.nabble.com/file/n33164/hyperpark.jpg)
(http://i47.tinypic.com/t7bqdj.jpg)
Title: Re: Low Gain, neutral dist/OD
Post by: Steben on August 03, 2019, 04:23:57 PM
What about a FF with buffered input?
Title: Re: Low Gain, neutral dist/OD
Post by: Killthepopular on August 03, 2019, 04:29:59 PM
What about a FF with buffered input?

What would the buffer do? Are fuzz faces a good choice for low gain stuff? I've never used one. Also I'm a bit wary of the whole transistor thing. Seems like FF designs tend to use weird transistors, especially germanium ones with the opposite power polarity, pnp I think they call it. I have seen ones that use 2n5088s though...

Fuzz faces have the lowest part count of any pedal I'm looking at and i love the sound. Guess I should definitely try it out.
Title: Re: Low Gain, neutral dist/OD
Post by: Fancy Lime on August 03, 2019, 05:05:47 PM
One of the nice things about the Tube Sound Fuzz Family of Overdrives (there are a lot of variants, some quite a bit more complicated), is that you can easily get a wide range of sounds by changing just one or two parts. If you have a breadboard, you should breadboard this to make sure you can figure out your personal favorite configuration. If you don't have one, get one and then breadboard it. Seriously, this will be much more useful for finding your sound than anything we can tell you. But of course you need to know what components do what. So (I am referring to the part numbers in the Catalinbread schematic that Mark posted for convenience, the basic topology is the same for all of these circuits):

The thing consists of two CMOS inverter stages (the right-pointing triangles with the circle at the point). The first stage contains C1, R1, C2, R2, and the Gain pot. The second stage contains C4, C5, and R4. The Gain of each stage is defined by the ratio between the resistance in the feedback loop to the resistance in front of the stage. For the first stage that means (R2 + Gain pot)/R1. You can view capacitors as frequency dependent resistors to understand what they do in their respective positions. At high frequency, the resistance of a capacitor is low and at low frequency it is high. This phenomenon is called reactance (https://en.wikipedia.org/wiki/Electrical_reactance). That means that C1 is part of a high pass and C2 is part of a low pass for the first stage. C4 and C5 do the same for the second stage. The gain of the second stage is not very well defined because it relies on the output impedance of the first stage. You can reduce the second stage gain by adding a resistor in series just after C4. In fact, I like this type of circuit best with a gain of 1 on the second stage, so I would make that resistor the same value as R4 (and would make both 470k or so). I strongly suggest playing around with different values for the resistors and caps and see what happens. It's a lot of fun. I would start with the values for the Tube Sound Fuzz or the Red Llama and then change one part at a time. Make it ten times the value it was or a tenth and see what happens. When you get a feeling for cause and effect, you can slowly sneak toward your perfect setup.

BTW, you can use a CD4049 or a CD4069 chip for all of these with little difference. Use what is easier to get but beware that the size and pinout are different.

A Fuzz Face would be a bit of an odd choice for clean to slightly gritty stuff. The transition into clipping will be much harsher than with the CMOS designs and the clipping itself will be harder. Not saying that's a bad thing, I personally like it a lot. But from your description I would not expect that that is what you are looking for. But if you are starting to build pedals, you will find out soon enough that the answer to the question "should I build this one thing or that other thing?" is usually "I'll just build both!". So by all means: Try it out! For a first time FF build, I would go with a NPN design using 2N3904 or 2N2222 transistors. 2N5088 are much higher gain and therefore not exactly everybody's cup of tea in a FF.

Hope that helps,
Andy
Title: Re: Low Gain, neutral dist/OD
Post by: cab42 on August 03, 2019, 05:06:17 PM
What about the Barber LTD? David Barber shared  the schematic in this thread

https://www.diystompboxes.com/smfforum/index.php?topic=72917.0

I have it on my build list and I even think I ordered the parts at some point.

Anyway, I look forward to hear what you end up with.
Title: Re: Low Gain, neutral dist/OD
Post by: ElectricDruid on August 03, 2019, 07:30:55 PM


what you describe is pretty much exactly Craig Anderton's Tube Sound Fuzz, aka the Way Huge Red Llama. Very natural and pleasing.

Yeah this looks like a really good suggestion. Lowest part count I've found so far, can do clean and  the tones sound good at low and high gain settings. And yeah, I'm no tube connoiseur but it sounds pretty tubey to me.
What's the sonic difference between those two versions of the same circuit?

Yeah, another +1 for TSF/Llama, an excellent idea. It's a good circuit to play with. Simple and lots of possibilities.
Title: Re: Low Gain, neutral dist/OD
Post by: GGBB on August 03, 2019, 10:17:23 PM
Along the lines of the TSV - the "Jiggle" side of the Double-D from ROG.
Title: Re: Low Gain, neutral dist/OD
Post by: iainpunk on August 04, 2019, 06:51:24 AM

(https://i.postimg.cc/8fQFCZ2c/embryo-green.png) (https://postimg.cc/8fQFCZ2c)
 this seems to be quite clean when turned down, but gets crisp and warm when pushed

Is it some sort of low gain fuzz?

not really a fuzz, more of an overdrive based on a design i found in an old text book from the tube era, it was designed to get maximum gain out of triodes, but jfet substitution works great
Title: Re: Low Gain, neutral dist/OD
Post by: Steben on August 04, 2019, 07:38:32 AM
What about a FF with buffered input?

What would the buffer do? Are fuzz faces a good choice for low gain stuff? I've never used one. Also I'm a bit wary of the whole transistor thing. Seems like FF designs tend to use weird transistors, especially germanium ones with the opposite power polarity, pnp I think they call it. I have seen ones that use 2n5088s though...

Fuzz faces have the lowest part count of any pedal I'm looking at and i love the sound. Guess I should definitely try it out.
A buffer eliminates the treble cut off of a classic FF circuit just after a guitar. With a pot in series with the input you can g get real low gain settings. The typical wooly sound of a FF is very much linked to the treble cut.

https://www.youtube.com/watch?v=pkSAFNdcr2Q

This vid poster prefers the boost before the FF, because it sounds more transparent...
Title: Re: Low Gain, neutral dist/OD
Post by: Killthepopular on August 04, 2019, 12:26:22 PM
The good ol' Electra distortion: http://fuzzcentral.ssguitar.com/schematics/electradistortion.gif
One of the most simple, yet amazingly good sounding little circuits. You might want to use two series pairs of Ge diodes instead of two singles and add a gain pot up front (wired like in the Jordan Bosstone: http://fuzzcentral.ssguitar.com/schematics/bosstoneschem.gif called "Attack" here). Or, simpler, just add a "softness" pot. See Arons mod tips: https://www.diystompboxes.com/cnews/mods.html #1 and #7, respectively. Still 10 parts or less.

I must have missed this post. I've looked into it. Found Joe Gore's premier guitar article about building a stompbox based around the electra. It sounds really good to me, like a less annoying version of the MXR Distortion +.
Title: Re: Low Gain, neutral dist/OD
Post by: Killthepopular on August 04, 2019, 12:41:31 PM
I don't want to overload myself so I think I'll just go ahead with the following 3 circuits:
Dod 250. Red Llama. Electra Distortion.

I'll order the parts soon.
Title: Re: Low Gain, neutral dist/OD
Post by: Steben on August 04, 2019, 12:48:52 PM
If you want simple, you could try Steby fuzz II:

https://www.diystompboxes.com/smfforum/index.php?topic=70765.0

You can even add diodes to ground as in an electra.
Title: Re: Low Gain, neutral dist/OD
Post by: roseblood11 on August 04, 2019, 02:16:00 PM
I don't want to overload myself so I think I'll just go ahead with the following 3 circuits:
Dod 250. Red Llama. Electra Distortion.

I'll order the parts soon.

From those three, the Llama might be the most neutral and natural sounding option. Instead of the DOD250, I'd suggest the Vox 1901, same circuit, but some different parts values. It needs a reverse logarithmic gain pot, just like the DOD - some layouts falsely show a log taper.
Title: Re: Low Gain, neutral dist/OD
Post by: Killthepopular on August 04, 2019, 05:03:20 PM
Instead of the DOD250, I'd suggest the Vox 1901, same circuit, but some different parts values. It needs a reverse logarithmic gain pot, just like the DOD - some layouts falsely show a log taper.

This seems like a good shout. Similar to the DOD but warmer, deeper, less fizzy distortion, more saturated and tubey. I actually watched the JHS video on 70s opamp distortion pedals and thought the guyatone sounded better than the dod but it was a bit thin. Voicing is very different from the vox. Must be some part substitutions.
Hm, something about the vox reminds me of those old marshall pedals.

(https://i.postimg.cc/5YQG4fdr/Vox-1901.png) (https://postimg.cc/5YQG4fdr)

What the hell is 1u/16? Should i just regard that as 1uf?

What's the deal with d4, r7, d3? Is that bypass stuff? I can't see any of that on the tagboard effects layout. Presumably i skip that stuff if I'm gonna ultimately be making a generic true bypass pedal?

I'll probably use 1n34a for the diodes.
Title: Re: Low Gain, neutral dist/OD
Post by: Rob Strand on August 04, 2019, 10:39:06 PM
Quote
This seems like a good shout. Similar to the DOD but warmer, deeper, less fizzy distortion, more saturated and tubey. I actually watched the JHS video on 70s opamp distortion pedals and thought the guyatone sounded better than the dod but it was a bit thin. Voicing is very different from the vox. Must be some part substitutions.
Hm, something about the vox reminds me of those old marshall pedals.

There's at least two versions of the DOD.  The earlier yellow ones (famous through Yngwie Malmsteen) have a 1nF input cap instead of a 10nF which is found in the grey ones.  That can thin-out the sound.  I don't mean the Yngwie Malmsteen pedal, as that is a re-issue of the yellow DOD overdrive.

At least one guyatone schematic I saw on line had a lot of errors (it should be the same as the VOX).


Quote
What the hell is 1u/16? Should i just regard that as 1uf?
1uF 16V

Quote
What's the deal with d4, r7, d3? Is that bypass stuff? I can't see any of that on the tagboard effects layout. Presumably i skip that stuff if I'm gonna ultimately be making a generic true bypass pedal?
It's just the LED circuit.  The zener makes the LED go out when the battery goes flat, a common trick.

FWIW,  for your pedal --> clean set-up I find all the MXR derivations a bit too harsh.   The pedals with the output filtering fair better.  TS9 is OK because it has the output filter but the midrange tone isn't as transparent as some like.  Some of the CMOS gate drives weren't bad.
Title: Re: Low Gain, neutral dist/OD
Post by: Killthepopular on August 05, 2019, 07:12:52 AM
clean set-up I find all the MXR derivations a bit too harsh.   The pedals with the output filtering fair better. Some of the CMOS gate drives weren't bad.

So you think I would probably want to filter some of the high end on the electra and the vox? Are we talking like a fixed RC LPF in the 2-4k range or more like a passive tone control like on a rat? If i added something like that would I need to add some boost circuitry after it to restore any lost output level?

What's a CMOS gate drive? Do you mean like the red llama?
Title: Re: Low Gain, neutral dist/OD
Post by: cab42 on August 05, 2019, 07:33:03 AM
Instead of the DOD250, I'd suggest the Vox 1901, same circuit, but some different parts values. It needs a reverse logarithmic gain pot, just like the DOD - some layouts falsely show a log taper.

This seems like a good shout. Similar to the DOD but warmer, deeper, less fizzy distortion, more saturated and tubey. I actually watched the JHS video on 70s opamp distortion pedals and thought the guyatone sounded better than the dod but it was a bit thin. Voicing is very different from the vox. Must be some part substitutions.
Hm, something about the vox reminds me of those old marshall pedals.

(https://i.postimg.cc/5YQG4fdr/Vox-1901.png) (https://postimg.cc/5YQG4fdr)

What the hell is 1u/16? Should i just regard that as 1uf?

What's the deal with d4, r7, d3? Is that bypass stuff? I can't see any of that on the tagboard effects layout. Presumably i skip that stuff if I'm gonna ultimately be making a generic true bypass pedal?

I'll probably use 1n34a for the diodes.

I have a vero layout for that in the gallery.

https://www.aronnelson.com/gallery/main.php?g2_view=core.DownloadItem&g2_itemId=3504&g2_serialNumber=3

It's for the Guyatone Zoom, but with a few different components it should work for the Vox.

Title: Re: Low Gain, neutral dist/OD
Post by: Killthepopular on August 05, 2019, 09:05:32 AM
Is there a stripped down neutral sounding (not mid focussed) tube screamer based circuit schematic that I could check out?
Title: Re: Low Gain, neutral dist/OD
Post by: Fancy Lime on August 05, 2019, 09:11:11 AM
...
What's a CMOS gate drive? Do you mean like the red llama?
Yes, the Red Llama (and the likes) can be considered a "CMOS gate drive", although "CMOS inverter drive" or something of the kind are more common terms.

BTW, you can also add a couple of diodes to ground (like in the DOD-250, Electra...) to the end of the Red Llama and see how that sounds. Make it switchable with a on/off/on switch to get "both diodes" / "no diodes" / "one of the diodes" and you'll have yourself quite a versatile drive pedal.

Andy
Title: Re: Low Gain, neutral dist/OD
Post by: Killthepopular on August 05, 2019, 12:09:15 PM
(https://i.postimg.cc/7GTtBgg5/Edited-TS9.png) (https://postimg.cc/7GTtBgg5)

(https://i.postimg.cc/ctR9W0kZ/tube-screamer-block-diagram.png) (https://postimg.cc/ctR9W0kZ)

I've had a bash at trimming down the tube screamer. What I think I've done is remove the input and output buffer, the bypass, the hpf in the clipping section, the lpf in the tone section and the tone control itself. Does it still make sense as a circuit?

EDIT: On second thought, it makes more sense for me to just use the ROG Tube Reamer and go from there. Those guys know what they're doing.
Title: Re: Low Gain, neutral dist/OD
Post by: Fancy Lime on August 05, 2019, 02:26:30 PM
(https://i.postimg.cc/7GTtBgg5/Edited-TS9.png) (https://postimg.cc/7GTtBgg5)

(https://i.postimg.cc/ctR9W0kZ/tube-screamer-block-diagram.png) (https://postimg.cc/ctR9W0kZ)

I've had a bash at trimming down the tube screamer. What I think I've done is remove the input and output buffer, the bypass, the hpf in the clipping section, the lpf in the tone section and the tone control itself. Does it still make sense as a circuit?

EDIT: On second thought, it makes more sense for me to just use the ROG Tube Reamer and go from there. Those guys know what they're doing.
Yes, your own schematic is missing a few caps and has some connections not quite right. Most importantly, the negative input of the opamps needs to be connected to ground via a DC-decoupling cap if you have a single sided power supply (as is the case for the vast majority of pedals including the Tube Screamer). You also need a resistor in there, else you get extremely high gain (so called open loop gain, meaning the maximum gain that the opamp is capable of) and unstable operation.
You are right, just build the Tube Reamer instead. That is almost the same as yours would be with the errors fixed.

Andy
Title: Re: Low Gain, neutral dist/OD
Post by: bluebunny on August 05, 2019, 03:12:48 PM
build the Tube Reamer instead

+1  :icon_cool:
Title: Re: Low Gain, neutral dist/OD
Post by: Rob Strand on August 05, 2019, 07:20:27 PM
A better example of a stripped down Tube-Screamer is Jack Orman's Son of Screamer,
http://www.muzique.com/tech/scream.htm

One way to remove some of the mid sound is to add a bit more of the lows back like the bass control in Timmy, see reply # 15,
https://www.diystompboxes.com/smfforum/index.php?topic=121481.0

This trick is used on many "Transparent" pedals eg.  Clark Gainster,  Menatone Red Snapper.   One method is to put a pot in series with the gain resistor (R2 on Son of Screamer).  Another method was the Tube-Screamer "Fat Switch" which increases the low-cut cap (C2 on Son of Screamer).   IIRC, Fulltone Fulldrive pedals are hard-wired with the Fat cap in place.

The Marshall Blues-Breaker adds an extra low-pass filter to get rid of the fizz, which is sometimes a good idea when your amp is set-up for clean.  It also cuts the lows more for high gain than low gain.

The problem with this stuff is there's no perfect solution.   Every few years a new golden transparent pedal comes out and it often turns out to be some sort of older circuit, many times a tube screamer variant (eg the Xotic stuff).
Title: Re: Low Gain, neutral dist/OD
Post by: cab42 on August 06, 2019, 06:50:20 AM
build the Tube Reamer instead

+1 from me too!

Try version 1, the one with a single opamp (741). I preferred this to version two. I'm not sure that the v. 1 schematic can be found on ROG anymore, but I think I have it somewhere.

Another suggestion. Earlier in the thread, Mark Hammer's AEFEA Drive was mentioned. I added a switch to mine, that removes the diodes from the feedback loop, and adds a diode pair to ground before the tone control.  It sounds great on lower gain settings!


Title: Re: Low Gain, neutral dist/OD
Post by: Killthepopular on August 06, 2019, 10:32:26 AM
I'm leaning away from the TS circuit. I'm getting the impression that it really is geared towards the mid focussed sound which I don't want and that it's not really straightforward to get a neutral tone from it (like with the red llama). Also I already have a modded SD1 and I'm not a huge fan of the TS sound anyway so it's probably a less worthwhile circuit for me to tinker with compared to some of these other circuits.

I appreciate the advice you guys have given thus far but I have to limit my options or I'm gonna be snowed under with circuit tinkering (instead of actually playing my guitar). Currently I'm leaning towards the following circuits. In no order:

1. Electra (Fancy Lime). ~ 9 components. It's really simple and sounds awesome.
2. Vox 1901 (roseblood11) 18 components. I love the Dod 250 and this sounds similar but warmer and smoother.
3. Red LLama (Fancy Lime, ElectricDruid) 14/15 components. This seems like it's the closest to my original conception of what I want from this project. It's pretty simple, it sounds kinda tubey and generally sounds nice. Also lots of you guys seem to think highly of this type of circuit.
4. Crowther Hotcake. 29 components. This is a bit of a curveball because it seems like a bit of a quirky circuit which doesn't really produce a "natural" crunch but it is well balanced overall and something about it has kind of captured my imagination. Scott Kannberg, guitarist in pavement (my favourite band) has pretty much just used this one dirt pedal for his whole career, so the Pavement affiliation adds to my interest.

I'll order the parts soon. I should probably get another breadboard while I'm at it. My current one (10X30 + power rails) is probably a bit cramped for a circuit like the hotcake.
Title: Re: Low Gain, neutral dist/OD
Post by: Steben on August 06, 2019, 02:09:57 PM
Natural transparent does not need to mean soft clipping typology. A low gain plexi can sound very natural, while it is rather hard clipping. Minibooster/mu amp circuits do not lip that soft either.
https://www.youtube.com/watch?v=GLE9Bo9B8F4
Title: Re: Low Gain, neutral dist/OD
Post by: Killthepopular on August 06, 2019, 05:05:29 PM
Natural transparent does not need to mean soft clipping typology. A low gain plexi can sound very natural, while it is rather hard clipping.
Good to know. I think the gritty, marshally, mesa boogie type sound is what i tend to like.
Title: Re: Low Gain, neutral dist/OD
Post by: Killthepopular on August 06, 2019, 05:28:14 PM
How capable is the electra of going from clean to dirty? Is it one of these LPB1 style transistor based circuits that is almost always a little dirty unless you roll your guitar volume right back? If I use a low gain transistor is it reasonably easy to get clean tones? Here's the boost part:
(https://i.postimg.cc/3Wmzg12d/Electra-boost.jpg) (https://postimg.cc/3Wmzg12d)
Title: Re: Low Gain, neutral dist/OD
Post by: Mark Hammer on August 06, 2019, 06:37:28 PM
The transistor does not have gain by itself.  It has the capability of higher gain (or not), depending on the biasing components around it.  In the case of the Electra circuit, the 2M2 resistor between collector and base helps to boost the gain, such that the signal has a high-enough amplitude to be clipped by the diodes.  I suppose if a person wished to, they could use a toggle to simultaneously lift the diode pair and change the effective value of R5.  Would reducing the gain of the transistor create significant level drop?  Not at the output, likely.  Keep in mind that the diodes remove peaks,  So by eliminating that diode action and reducing the gain, you may well end up with the same final output level.
Title: Re: Low Gain, neutral dist/OD
Post by: Rob Strand on August 06, 2019, 08:56:56 PM
Quote
4. Crowther Hotcake. 29 components.
Along the lines of the The Hotcake and the perhaps the FullDrives with feedback you should perhaps check out the "One Control" Honey Bee; BTW it has three controls.    That one is one of the later incarnations of that type of circuit.  There's schematics and layouts on-line - the cap across pins 1 and 8 should be 100p.   You probably don't want the Honey Beest as that has an extra gain stage.  I have *not* build either of these. You can find clips on youtube.   To me it's just a tad muddy on some clips but not on others.

You could even try removing the last gain stage.

It uses a CMOS CA3130 opamp.
Title: Re: Low Gain, neutral dist/OD
Post by: garcho on August 06, 2019, 11:02:30 PM
Clean to distorted without a frog leap or “fizzle” can be done perfectly by blending in a little  dry signal with overdrive signal made from diodes in the feedback path of an op amp. Combine the two in a summing amplifier configuration. Along with either your picking velocity or volume knob stuff, it sounds linear, from clean to velcro. Add a treble-cut knob and call it a day. Perfect for chords, 3rds/6ths sound clean, but then riffs and licks can still sound nice and fuzzy with a little more knuckle grease.
Title: Re: Low Gain, neutral dist/OD
Post by: Killthepopular on August 07, 2019, 11:41:07 AM
I'm going ahead with the four circuits mentioned above. Electra. Vox distortion. Red Llama. Hotcake.

Just writing up a list of all the parts I need.

Just checking, 50k-RA is the same as C50k right?
Title: Re: Low Gain, neutral dist/OD
Post by: Mark Hammer on August 07, 2019, 01:41:44 PM
No.  They have the reverse taper.  That said, if you flip which wires go to the outside lugs, and are willing to have clockwise = "less", rather than "more", a C and A taper will work identically with respect to dialability.
Title: Re: Low Gain, neutral dist/OD
Post by: Rob Strand on August 07, 2019, 06:59:24 PM
Quote
Just checking, 50k-RA is the same as C50k right?

Quote
No.  They have the reverse taper.  That said, if you flip which wires go to the outside lugs, and are willing to have clockwise = "less", rather than "more", a C and A taper will work identically with respect to dialability.
Normall "-RA" = Reverse Audio which is the same as C.   Whereas  50kA or A50k are just normal Audio ("A")  taper which are different but can be used in reversed with some inconvenience.

Quote
Clean to distorted without a frog leap or “fizzle” can be done perfectly by blending in a little  dry signal with overdrive signal made from diodes in the feedback path of an op amp. Combine the two in a summing amplifier configuration. Along with either your picking velocity or volume knob stuff, it sounds linear, from clean to velcro.
Interestingly the feedback diode configuration naturally adds some clean *provided* the opamp with the feedback diodes doesn't clip.   However the clean in this case get filtered by the tone control.

Quote
Add a treble-cut knob and call it a day. Perfect for chords, 3rds/6ths sound clean, but then riffs and licks can still sound nice and fuzzy with a little more knuckle grease.
Actually adding a lot-pass filter, or treble control to the Vox/MXR/DOD circuit goes a long way to take the sizzle out.    The 10k resistor and the 100k volume pot make it more difficult to get the filter to work.   Reducing the 10k to 1k or 2k can help but it does change the sound a little bit.  The volume control loads the tone control filter so it's best to add a buffer.  I guess the way the Rat does the tone control is the best example of that; you don't need a JFET for the buffer you can use an opamp.  The other way to do it is to put the tone control after the volume pot but then the filter frequency moves about a bit with different volume control settings and with the cable capacitance.

If I was putting a fixed filter in there I'd probably go for about 6kHz or so.   IMHO a good balance between removing sizzle and not losing 'air' from the clean tone.  If you look at the fixed filters in the tube-reamers the fixed filters are 4.8kHz on the old and 7.2kHz on the new.  This is right in the the zone.  4.8kHz can be a little dark and 7.2kHz will start to bring back the natural air but also has more sizzle.

Back in 2001/2003 I put up simple example circuit of a diode clipper with a RAT type control together with a clean blend.  I chopped and changed between output clipping and feedback clipping.   Each have their own sound.

Title: Re: Low Gain, neutral dist/OD
Post by: Rob Strand on August 08, 2019, 11:06:17 PM
FWIW, here's a way to add a control to the DOD 250.
(For the tone control: The C taper isn't going to be fairly ineffective for the half the rotation so maybe the B taper is better here ).


(https://i.postimg.cc/GHb85TcP/Simple-DOD250-Tone-Control-V1-1.png) (https://postimg.cc/GHb85TcP)
Title: Re: Low Gain, neutral dist/OD
Post by: Steben on August 10, 2019, 08:06:50 AM
https://www.youtube.com/watch?v=lH4xD8W-7Io

Check this out, the axis face. A silicon fuzz face that cleans up very well with single coils.
This is greatly there due to the 100k pot in front. This flattens the input impedance by adding resistance. Since the silicon fuzz has bigger gain, this results in a smooth result at gains comparable to germanium but with less farty wool.
(https://fuzzcentral.ssguitar.com/axisface/axisfacesi3schematic.gif)
Title: Re: Low Gain, neutral dist/OD
Post by: Killthepopular on August 11, 2019, 06:27:02 AM
I've set up the electra circuit and am trying different diodes. Red LED, 1n34a, 1n914. So far I've done:

LED
LED - Something warm and classy about LED but it sounds very un-amplike. The big test seems to be how well a diode combo can handle droning fingerpicked arpeggios. This technique creates a wall of sound which you want to be very slightly fuzzy all the time. LEDs seem to throw in farty sounding clipping at random intervals. Sounds awful. Seems like LEDs are good for a hard crunch but not good for smooth valvey tones.

Si
Si - A bit shrill and nasty sounding though maybe more solid than germanium. The clipping is a bit nicer than LED but seems to make the tone a bit harsh.

Ge
Ge - The best so far, sounds very smooth and natural and amp-like.

gonna try the following five combinations:

Ge Ge
Ge

Ge Ge
Si

Ge Si
Si

Ge Ge
LED

Ge Si
LED
Title: Re: Low Gain, neutral dist/OD
Post by: Rob Strand on August 11, 2019, 07:53:25 AM
Quote
I've set up the electra circuit and am trying different diodes.
What collector voltage are you operating at?  I can affect the sound quite a bit.
A good starting point would be 4.5V but should try tweaking the bias point up and down from that a see if the sound is more appealing to you.
Title: Re: Low Gain, neutral dist/OD
Post by: Killthepopular on August 11, 2019, 08:07:19 AM

What collector voltage are you operating at?  It can affect the sound quite a bit.
tranny is 2n3904. using standard 9v batt.

(https://i.postimg.cc/CdvbyYPB/Electra-boost.jpg) (https://postimg.cc/CdvbyYPB)
Title: Re: Low Gain, neutral dist/OD
Post by: PRR on August 11, 2019, 04:29:59 PM
What collector voltage are you operating at?
Title: Re: Low Gain, neutral dist/OD
Post by: Killthepopular on August 11, 2019, 05:43:10 PM
What collector voltage are you operating at?

Is that the measurement between pin 3 and ground? it says 2.18v. I've now swapped r1 2m2 with a 10m. This reading is now at 4.7v. Is this more or less correect?

Based on my tests so far I find that germanium seems to have a more natural, valve-like clip than silicon or LED.
Silicon seems to give a bigger and deeper tone than LED and has more natural clipping, but silicon also adds some slightly ugly harmonics which make things a bit shrill. LED clipping sounds weirder than silicon but it doesn't seem to add shrillness in the same way silicon does.
Asymmetric clipping is maybe a bit bigger, more dynamic, less compressed sounding than symmetric.
Title: Re: Low Gain, neutral dist/OD
Post by: Killthepopular on August 12, 2019, 02:17:29 PM
I'm finding that Asymmetric can start sounding subtly distorted so you aren't sure if the sound is clean or distorted. It sounds like a mix of clean and dirty. Whereas Symmetric clipping seems to instantly go from very clean to very distorted with a quick turn of the gain knob. It's less good at sounding slightly distorted.

I've also found that headroom seems to make a big difference. When I compare 2 silicon diodes with 4 silicon diodes (one on either side vs 2 in parallel on either side) I find that the 2 diodes give me a smaller, thinner, harsher tone with less bass. 4 diodes however gives me a much warmer, bassier, darker, looser, less tight sort of sound. I'm adjusting the gain and volume pots to give me the same amount of gain and level in both instances.

What am I hearing here? Is this a standard consequence of higher headroom? Or am I hearing something else? Maybe turning down the output means that the impedance that my amp receives changes and so it sounds deeper and darker because high end is being lost? Is it normal for higher headroom to yield a darker, warmer tone?
Title: Re: Low Gain, neutral dist/OD
Post by: Mark Hammer on August 12, 2019, 04:05:27 PM
Use a pair of germanium or schottky, but insert a 500R-1k pot between the diodes and ground.  That will provide for some very hard clipping (albeit with low output), but the ability to soften the clipping as that resistance to ground is increased.
Title: Re: Low Gain, neutral dist/OD
Post by: Rob Strand on August 12, 2019, 07:36:12 PM
Quote
I'm finding that Asymmetric can start sounding subtly distorted so you aren't sure if the sound is clean or distorted. It sounds like a mix of clean and dirty. Whereas Symmetric clipping seems to instantly go from very clean to very distorted with a quick turn of the gain knob. It's less good at sounding slightly distorted.
The Electra circuit isn't 100% symmetrical itself.  When the circuit clips the output impedance isn't constant like and opamp. In the positive direction you have up to 68k and in the negative direction you have 0 to 10k depending on you trimpot value. 

The 100k level pot is actually pretty low compared to the 68k.  IIRC the original Electra circuit used 4k7 collector resistor which helps reduce the output impedance.  There's many variants over the web, I know I've seen a 10k version as well. You will need to adjust the other resistor values to compensate for changes in the collector resistor.

(http://beavisaudio.com/schematics/Images/Electra-Distortion-Schematic.png)

You can put resistor in series with the output cap to make the impedance more symmetric but it's probably only worthwhile if you have a lower collector resistor.

The Electra circuit isn't exactly 100% transparent since it loads the pickup.  The design which uses the 68k resistor will load the pickup less and the design with 4k7 will load the pickup more.  So there's a bit a of a balancing act keeping all the non-ideal behaviour in check.

Title: Re: Low Gain, neutral dist/OD
Post by: Killthepopular on August 13, 2019, 11:26:37 AM
I think I'll definitely go with Asymmetric clipping. It does a very good job of slowly getting subtly dirtier (Which is what I want for this project), whereas symmetric clipping seems more prone to being either totally clean or totally gritty.

I Like 1n4001 and 1n34a diodes the most. I might use a combination of those or maybe just 3 1n4001s. I've also ordered some 1n5817s because someone suggested trying a schottky.

What happens when I have two different types of diodes in series? Say I have an LED and a 1n34a. I understand that the forward voltage or headroom will be equivalent to both of them added together, but what about the tone? Will i get something that's halfway between the two tones? I've read that the lower voltage diode (1n34a) will turn on first so you'll get the tone of just that one diode but at a higher headroom. Does that sound correct?
Title: Re: Low Gain, neutral dist/OD
Post by: Mark Hammer on August 13, 2019, 06:17:00 PM
Anything you do to increase the forward voltage required for the diodes to conduct will have three consequences:
1) It will take a hotter signal to result in any clipping,
2) Any clipping produced will be for a shorter portion of the note's lifespan (since less of the signal will be above threshold),
3) With headroom increased, the maximum output level will be higher.

The "tone" produced by any given type of diode is largely a function of how its' respective forward voltage affects that stuff.  I find there's a lot of stuff that people attribute to magical diode properties that simply results from forward voltage.  Diodes DO differ in many characteristics, but many of those characteristics are more relevant to signal switching at speeds >500khz that to the puny 6khz bandwidth guitars produce.

Following that logic, sticking several Schottky diodes in series, to achieve the same total forward voltage as a silicon type, will get you the same clipping as that silicon type.  It will NOT get you a tone that is any sort of blend of what schottkys or germanium alone would get.  I understand that conduction speed can vary with the current feeding them, but that's typically something you can tweak with whatever resistor is in series with the signal.

So, if you want hard clipping you can either raise the gain so that more of the signal falls above the clipping diodes' forward voltage, or you can reduce the forward voltage of the diodes by making different diode choices.  Conversely, if you want less clipping, you can either lower the gain, or raise the clipping threshold...or both.
Title: Re: Low Gain, neutral dist/OD
Post by: Rob Strand on August 13, 2019, 07:18:17 PM
Quote
What happens when I have two different types of diodes in series? Say I have an LED and a 1n34a. I understand that the forward voltage or headroom will be equivalent to both of them added together, but what about the tone? Will i get something that's halfway between the two tones? I've read that the lower voltage diode (1n34a) will turn on first so you'll get the tone of just that one diode but at a higher headroom. Does that sound correct?
Suppose you have two identical diodes and put them in series.   The intrinsic "tone" of that combined diode is the same a single diode.  However, it becomes difficult to compare apples to apples:   The voltage drop of the combined diode is now double but the voltages in the rest of the circuit have not doubled.  So even though the intrinsic tone of the combined diode hasn't changed the circuit as a whole will sound different.

So suppose we ignore the fact the sound of the *whole circuit* changes due to different voltage drops then we can say something:  The tone of putting two diodes in series is a mix of the two diodes, however it's not as simple has half of one and half of the other.  The tone is weighted towards the diode with the larger voltage drop.   This formula, kind of represents what happens,

      combined diode tone  =   (VD1 * "tone of diode 1"  + VD2 * "tone of diode 2") / (VD1 + VD2)
      where VD1 is the voltage drop of diode 1 and VD2 is the voltage drop of diode 2.

So adding a germanium to an LED is like adding a dash of germanium salt as the LED voltage drop is much larger and dominates the tone.

Notice that formula shows two identical diodes having the same tone.
Title: Re: Low Gain, neutral dist/OD
Post by: Steben on August 21, 2019, 02:36:17 PM
https://www.facebook.com/ArgenzianoEffetti/videos/1084476765074158/

Check this out... Silicon Fuzz face clean up. Love it!
Title: Re: Low Gain, neutral dist/OD
Post by: Rob Strand on August 21, 2019, 07:12:54 PM
Quote
Check this out... Silicon Fuzz face clean up. Love it!
Ah, I can't see videos on Facebook.
Was there a schematic?   (Adding caps around the transistors can help.)
Title: Re: Low Gain, neutral dist/OD
Post by: Killthepopular on August 23, 2019, 06:30:03 AM
I built the electra and fiddled with loads of different diodes and settled on an asymmetrical configuration of 1n4001 diodes. I think it's best for what I want. Does a good off clean tone and has a nice warm fuzzy quality.

Moved onto the red llama. Very impressed with it. Doesn't give loads of gain but if you want lots of gain it takes boosts shockingly well and seems to have a ton of output too, so it doesn't have a lot of it's own gain but could easily fit into a high gain setup. Sounds really good at low gain. Very natural and amp-like. None of that on/off, sputtery clipping that you get from standard distortion setups. Doesn't seem to colour the sound and only gets slightly brighter as you push it harder. Very good all round. Probably trumps the electra all in all. Will probably move onto the vox distortion next.

Thanks to the three or four guys who recommended the red llama. I didn't know anything about this circuit but it seems like a really great circuit as well as being a close match to what I wanted. I still have two more circuits to try but I find it hard to imagine that I'll like them more than the Llama.
Title: Re: Low Gain, neutral dist/OD
Post by: Fancy Lime on August 23, 2019, 12:04:07 PM
You're welcome! That's what this forum is for, among other things.

Cheers,
Andy
Title: Re: Low Gain, neutral dist/OD
Post by: Rob Strand on August 23, 2019, 11:03:39 PM
Quote
Thanks to the three or four guys who recommended the red llama. I didn't know anything about this circuit but it seems like a really great circuit as well as being a close match to what I wanted. I still have two more circuits to try but I find it hard to imagine that I'll like them more than the Llama.
Maybe you should tinker around with variations of those CMOS gate based overdrives.

The Laney amps have used CMOS gate based overdrives for quite some time.  You might get some ideas by looking at the circuits.  Some channels have more gain than others.

For example,
Laney pl50rh
https://elektrotanya.com/laney_pl50rh_schematic.pdf/download.html
Fairly sure cmos devices are running from 5V (trimpots adjusted for 3.1V at outputs).

Some others were Laney hc25, Laney hcm65r.
A lot of the HC and HCM models.

You can play with the supply voltage and also add resistors to shift the DC bias points at the outputs of the gates.   IIRC some of the Laney schematics have trimpots and show the voltages they use.
Title: Re: Low Gain, neutral dist/OD
Post by: Killthepopular on August 24, 2019, 10:14:20 AM

Maybe you should tinker around with variations of those CMOS gate based overdrives.

The Laney amps have used CMOS gate based overdrives for quite some time. 

I'll test these 2 remaining circuits (vox dist and hotcake) and If the red llama is my fave then I'll mod it a bit before I start thinking about laying it on vero or perf. I might also want to stick a simple pre-overdrive boost (LPB1 or SHO) with a footswitch in the same enclosure too.

My main amp is actually a laney LV100. Do you know if that uses a cmos type overdrive?
Title: Re: Low Gain, neutral dist/OD
Post by: Killthepopular on August 24, 2019, 01:17:09 PM
I'd suggest the Vox 1901, same circuit, but some different parts values. It needs a reverse logarithmic gain pot, just like the DOD - some layouts falsely show a log taper.

Doh! I remember reading this but I must have forgotten and ordered a log pot. Can I just connect it up backwards and get the same taper? Albeit with a knob that increases gain when you turn it counter-clockwise?
Title: Re: Low Gain, neutral dist/OD
Post by: Rob Strand on August 24, 2019, 07:20:45 PM
Quote
My main amp is actually a laney LV100. Do you know if that uses a cmos type overdrive?
I'm not sure about that model I've got no info on it. 
Title: Re: Low Gain, neutral dist/OD
Post by: roseblood11 on August 24, 2019, 07:34:32 PM
I'd suggest the Vox 1901, same circuit, but some different parts values. It needs a reverse logarithmic gain pot, just like the DOD - some layouts falsely show a log taper.

Doh! I remember reading this but I must have forgotten and ordered a log pot. Can I just connect it up backwards and get the same taper? Albeit with a knob that increases gain when you turn it counter-clockwise?

Yes, no problem.
And that circuit sounds good with a SHO in front of it
Title: Re: Low Gain, neutral dist/OD
Post by: Killthepopular on September 11, 2019, 10:06:18 AM
So I've tried the 4 circuits. Electra was good but maybe a bit samey sounding. Red Llama was really impressive. Dod 250/vox distortion was awesome but not really a natural amp-like sound. Hotcake was cool but a long way from having amp-like qualities.

Think I'll give the peppermill a go. It sounds pretty bad to me from the clips but a lot of people seem to really like it and I have most of the bits and it looks very easy to breadboard.

http://www.runoffgroove.com/peppermill.html

I don't have 6.8n or 2.2 n but I have 10n and 1n. Also I don't have B250k but I do have B50k or A250k. Will those substitutions work ok? Just for a quick breadboard layout.
Title: Re: Low Gain, neutral dist/OD
Post by: snk on September 11, 2019, 10:30:44 AM
I built the Red Llama last week.
It didn't sound the way i expected(i wanted it a bit darker and less saturated), so, thanks to the helpful community here i have tweaked it quite a lot (https://www.diystompboxes.com/smfforum/index.php?topic=123036.0) and now it's very good.

I have also heard people raving about the Fairfield Barbershop, but i haven't tried it yet.
Title: Re: Low Gain, neutral dist/OD
Post by: Ben N on September 11, 2019, 01:35:21 PM
This might also be worth a look: http://revolutiondeux.blogspot.com/2012/04/soulsonic-folk-driver.html (http://revolutiondeux.blogspot.com/2012/04/soulsonic-folk-driver.html)
Title: Re: Low Gain, neutral dist/OD
Post by: GGBB on September 11, 2019, 01:51:30 PM
I don't have 6.8n or 2.2 n but I have 10n and 1n. Also I don't have B250k but I do have B50k or A250k. Will those substitutions work ok? Just for a quick breadboard layout.

6n8 is a high pass filter. Bigger means more bass/flub, smaller means thinner.

2n2 is a low pass filter. Bigger means duller, smaller means brighter.

A250k will work fine but adjustment will be crowded at the clockwise end.
Title: Re: Low Gain, neutral dist/OD
Post by: Killthepopular on September 11, 2019, 04:48:18 PM
6n8 is a high pass filter. Bigger means more bass/flub, smaller means thinner.

2n2 is a low pass filter. Bigger means duller, smaller means brighter.

A250k will work fine but adjustment will be crowded at the clockwise end.
Ok, I'll try both options and go with what sounds better. Oops, I meant to say I have A500k. I'm sure it'll work more or less anyway.
Title: Re: Low Gain, neutral dist/OD
Post by: GGBB on September 11, 2019, 07:00:52 PM
Ok, I'll try both options and go with what sounds better. Oops, I meant to say I have A500k. I'm sure it'll work more or less anyway.

The pot and the 100k below it act as a voltage divider off of the MOSFET output into the JFET configured as a standard volume control. The 100k sets the minimum gain level relative to the total resistance. So 500k will give you additional lower gain settings without changing the max gain (which is always max/total resistance). But the total resistance also forms the other half of the high pass filter with the 6n8, so change the total resistance and you also change the filter cutoff - more resistance means more bass/flub, less means thinner. If you change the overall resistance of that divider, you should also change the cap in the other direction by the same factor to compensate and maintain the same value for the low pass filter cutoff. So with 500k plus 100k, you would want to change 6n8 to 3n9 (math: 6n8 / ((500k + 100k) / (250k + 100k))).

You can also use your B50k (so as to keep the same taper) and change the connected 100k to 20k (substitute 22k or 18k) and change 6n8 to 33n. That should also give you close to the same result as original spec.
Title: Re: Low Gain, neutral dist/OD
Post by: Killthepopular on September 12, 2019, 04:45:28 AM

You can also use your B50k (so as to keep the same taper) and change the connected 100k to 20k (substitute 22k or 18k) and change 6n8 to 33n. That should also give you close to the same result as original spec.

I have 22kr and 33n so I'll use this option. Cheers.

The LPF calls for 8.2k+2.2n=8.8khz. My options are:
13k+1n=12khz
22k+1n=7.2khz
1k+10n=16khz
3.3k+10n=4.8khz

I think I'll go for 22k+1n=7.2khz.
Title: Re: Low Gain, neutral dist/OD
Post by: Killthepopular on September 12, 2019, 11:10:00 AM
What's the deal with J201s? I'm checking the voltage of the j201 Drain and it's like it changes every minute for no reason. I've set up a voltage divider with 2 10k resistors. The output of that divider is 4.5v~. I connect it to my J201 drain. Check the drain voltage. 4.5v. Great. I check it again a minute later. 3.3v. What? Now it seems to be back at 4.5. Am I doing something seriously wrong or is this normal behaviour for jfets?

Wait. It's something to do with me touching the other legs with my multimeter probe. This seems to screw with the drain voltage somehow and drop it down to 3.3v. I swap to another one that I haven't checked in a while and it's at 4.5v again. Am I screwing with the latent charge of these transistors or something?

EDIT: Looks like I had set it up so that the resistor below the gain pot wasn't connected to the gain pot. The circuit seems to sound and work ok now.
Title: Re: Low Gain, neutral dist/OD
Post by: Sooner Boomer on September 12, 2019, 01:26:52 PM
A couple of things to think about, and save for future reference;

A good analysis of the Tube Screamer, including how the tone control section works, including frequency response graphs  https://www.electrosmash.com/tube-screamer-analysis

Presence/tone control based on the Big Muff tone stack; http://www.muzique.com/lab/tone3.htm      (all of Jack's stuff is worth reading)
Title: Re: Low Gain, neutral dist/OD
Post by: PRR on September 12, 2019, 02:12:56 PM
> Am I screwing with the latent charge of these transistors

If the Gate is floating, no resistor toward Source, the FET state is unknown past history of charge.

FET/Tube Gates/Grids must ALWAYS have a known bias.
Title: Re: Low Gain, neutral dist/OD
Post by: Rob Strand on September 12, 2019, 05:04:33 PM
Quote
The LPF calls for 8.2k+2.2n=8.8khz. My options are:
13k+1n=12khz
22k+1n=7.2khz
1k+10n=16khz
3.3k+10n=4.8khz

One thing about that circuit is the output impedance of the JFET stage needs to be included in the filter calculation.  As drawn that means anything for 0 to 50k!   A 50k there in series with the 8k2 is going to have more effect that the 8k2 itself.  In practice the uncertainty won't be as wide 0 to 50k.   A typical value might be 18k to 20k (that's not the expected range of uncertainty though).
Title: Re: Low Gain, neutral dist/OD
Post by: GGBB on September 12, 2019, 06:58:56 PM
The LPF calls for 8.2k+2.2n=8.8khz. My options are:
13k+1n=12khz
22k+1n=7.2khz
1k+10n=16khz
3.3k+10n=4.8khz

I think I'll go for 22k+1n=7.2khz.

If you have a spare 10k pot - you can use that with a 10n cap connected to the wiper and have an adjustable tone control.
Title: Re: Low Gain, neutral dist/OD
Post by: Killthepopular on September 13, 2019, 07:49:15 AM
I like the peppermill more than I expected so I'll buy the parts and try it properly. I'll buy some parts for two other circuits I wanna try while I'm at it; ROG Eighteen and Fairfield Barbershop. Ordering now.
Title: Re: Low Gain, neutral dist/OD
Post by: Killthepopular on September 26, 2019, 04:58:31 PM
Had another go with the peppermill with the proper components (no substitutions). It's cool but it sounds a bit transistory to me. Not really what I'm looking for.

Can someone help me with the pinout for the vp3203 on the barbershop? I can't find it with google.  Also, I notice that the tagboard effects version of the barbershop seems to omit q4, r11 and r10. Are they somewhat superfuous parts of the circuit?

http://4.bp.blogspot.com/-Roy4uUPtPQ8/T-oMZ3fHO4I/AAAAAAAABv0/0IPFOReE0QU/s1600/Fairfield+Circuitry+-+The+Barbershop.png


(https://i.postimg.cc/VdCL5KLB/Barbershop.png) (https://postimg.cc/VdCL5KLB)
Title: Re: Low Gain, neutral dist/OD
Post by: Rob Strand on September 26, 2019, 06:08:00 PM
Quote
Can someone help me with the pinout for the vp3203 on the barbershop? I can't find it with google.  Also, I notice that the tagboard effects version of the barbershop seems to omit q4, r11 and r10. Are they somewhat superfuous parts of the circuit?
You can leave those out. Probably a good idea to keep R10, maybe make it 100R.

The motivation appears to be polarity protection but that circuit is going to be hard to fry,
http://www.geofex.com/Article_Folders/mosswitch/mosswitch.htm

Title: Re: Low Gain, neutral dist/OD
Post by: PRR on September 27, 2019, 12:43:46 AM
> pinout for the vp3203

http://ww1.microchip.com/downloads/en/DeviceDoc/VP3203%20B082613.pdf

Agree it isn't essential.
Title: Re: Low Gain, neutral dist/OD
Post by: Killthepopular on September 27, 2019, 05:03:51 AM

You can leave those out. Probably a good idea to keep R10, maybe make it 100R.

Like this?


(https://i.postimg.cc/ThxdcXH6/Barbershop-power.jpg) (https://postimg.cc/ThxdcXH6)
Title: Re: Low Gain, neutral dist/OD
Post by: Ben N on September 27, 2019, 05:13:01 AM
I like the peppermill more than I expected so I'll buy the parts and try it properly. I'll buy some parts for two other circuits I wanna try while I'm at it; ROG Eighteen and Fairfield Barbershop. Ordering now.
This is how it begins. Get away now, while you still can, I tell ya!
(https://i.imgur.com/YGLd64X.png)
Title: Re: Low Gain, neutral dist/OD
Post by: Killthepopular on September 27, 2019, 06:17:36 AM
(https://i.postimg.cc/VdCL5KLB/Barbershop.png) (https://postimg.cc/VdCL5KLB)

Out of interest, what is the function of c6 and r12? Most volume pots I've seen so far just have one of the pins as the audio output without any further components. Something to do with impedance or filtering low end?
Title: Re: Low Gain, neutral dist/OD
Post by: Killthepopular on September 27, 2019, 07:28:01 AM
Fairfield seems to be working ok. Although there was a burning smell coming from my amp when I first turned it on... Maybe there's just an insane amount of gain available with the fairfield and something in the input stage of my amp was getting overloaded (marshall valvestate).

It sounds pretty cool although It still sounds pretty transistory. It's possible that I don't really care for the sound of transistors being overloaded. I think maybe the tone, once you get a certain amount of crunch, becomes a little too crispy, and I prefer something more muddy and squishy. It's like the sound is too hard, not enough give. Germanium fuzz faces sound cool but I guess those are a rather different beast. I love the sound of distortion circuits like the 250 and the DS1 but those usually aren't so good with the subtle breakup tones.
Title: Re: Low Gain, neutral dist/OD
Post by: Ben N on September 27, 2019, 07:32:54 AM
(https://i.postimg.cc/VdCL5KLB/Barbershop.png) (https://postimg.cc/VdCL5KLB)

Out of interest, what is the function of c6 and r12? Most volume pots I've seen so far just have one of the pins as the audio output without any further components. Something to do with impedance or filtering low end?
Decoupling and setting the output impedance.
Title: Re: Low Gain, neutral dist/OD
Post by: Rob Strand on September 27, 2019, 07:15:34 PM
Quote
Like this?
That way is fine.

The topic of protection has come-up many times and I guess the consensus is these days is a Schottky diode in series with the +rail has some advantages (and some small disadvantages)
Title: Re: Low Gain, neutral dist/OD
Post by: PRR on September 28, 2019, 04:01:30 PM
> Decoupling and setting the output impedance.

COUPLING!

De-coupling takes the sneakage out of sneak-paths, like via the power rail.

Coupling passes AC, not DC, from one part to the next. Also "blocking", depending how you think.

Yes, this mild cheat has ~~5V of DC on the Volume pot. We do not want that to upset the next pedal/amp, C6 is a coupling or blocking cap. If a heavy capacitive load (long cable) falls on an emitter follower, it can oscillate radio waves. It can also try to flow "infinite" current. R12 ensures that whatever junk you hang on the output there is enough dead resistance to limit bad effects.
Title: Re: Low Gain, neutral dist/OD
Post by: Ben N on September 28, 2019, 05:05:29 PM
Whoops!  :-[ Thanks for the correction, Paul.
Title: Re: Low Gain, neutral dist/OD
Post by: Killthepopular on October 03, 2019, 10:20:33 AM
I've been using some of these circuits in some songs.

This one uses the hotcake
https://youtu.be/A5-8A85gcw4

The solos on this one use the electra circuit.
https://youtu.be/lFy52vLCqvs

This one uses the ROG Eighteen on bass and guitar.
https://youtu.be/PxT1HyCNNdE
Title: Re: Low Gain, neutral dist/OD
Post by: Killthepopular on October 17, 2019, 05:23:31 PM
So far I've tried 7 different circuits and the only one that actually does what I want is the red llama. I've got another 3 I wanna try. There's the son of screamer which looks pretty straightforward.

I wanna do an OCD.


(https://i.postimg.cc/fJLksn66/ocd-schem.gif) (https://postimg.cc/fJLksn66)

I'm gonna swap the tl082 with a tl072 and the 2n7000 with the bs170. Apparently these are valid swaps. Also I'm guessing that that stuff in the top right is a bypass buffer which isn't necessary for a breadboard build of this circuit. And what kind of switch do I need for the lp/hp switch?

The other one I really want to try is the nobels ODR1 although it's a bit more complex than anything else I've tackled.


(https://i.postimg.cc/Pp5N5gCp/Nobels.jpg) (https://postimg.cc/Pp5N5gCp)

Is there some buffer stuff here that I can leave out? The j201 stuff looks like an input buffer to me and the stuff after the level pot looks like an output buffer...
Title: Re: Low Gain, neutral dist/OD
Post by: bluebunny on October 18, 2019, 03:47:59 AM
I'm gonna swap the tl082 with a tl072 and the 2n7000 with the bs170. Apparently these are valid swaps.
. . .
And what kind of switch do I need for the lp/hp switch?

The 082 is a lower-noise version of the 072.  The 2N7000 and BS170 are interchangeable, but the pinout of one is spun 180o relative to the other.

The switch is a simple SPST - closed is HP, open is LP.  Or else use two adjacent lugs on an SPDT if that's all you've got to hand.
Title: Re: Low Gain, neutral dist/OD
Post by: Ben N on October 18, 2019, 05:30:54 AM
So far I've tried 7 different circuits ...I wanna do an OCD.

Seems like you're already well on your way there!  :icon_mrgreen:
Title: Re: Low Gain, neutral dist/OD
Post by: dennism on October 18, 2019, 08:09:31 AM
"Seems like you're already well on your way there!"


I see what you did there!
Title: Re: Low Gain, neutral dist/OD
Post by: Killthepopular on October 18, 2019, 09:41:18 AM
So far I've tried 7 different circuits ...I wanna do an OCD.

Seems like you're already well on your way there!  :icon_mrgreen:

I'm hopefully going to eventually make a generic, good sounding dirt pedal which I can just have on all the time as my default base tone. I feel like I ought to try a lot of different circuits before I settle on one, seeing as I hope to use it all the time for the indefinite future. Other guys would cycle through a dozen pedals until they found one that stayed on their board for years. I intend to breadboard numerous pedals then build my favourite instead of buying and selling loads. Actually come to think of it, guitarists' relationship with dirt pedals sounds kinda similar to marriage. They play the field for a while. They can never quite commit to any one pedal. But then they find "the one" and they never take it off their board. Maybe they still fool around a little on the side but they can never bring themselves to leave "the one".

Other circuits I've considered building but not convinced by: Rat (not fussed). Jackhammer (awesome but complicated and probably too hard clipped to be a good always on pedal). Barber LTD (sounds ok). Bluesbreaker (not a fan but I know they're popular). Sweet honey (nice but sounds a bit fuzzy). Timmy (sounds kinda mediocre to me...).

If no-one can suggest any edits to the nobels circuit I guess I'll just build the whole thing... though I'll probably need a bigger breadboard...
Title: Re: Low Gain, neutral dist/OD
Post by: Fancy Lime on October 18, 2019, 03:27:15 PM
So far I've tried 7 different circuits ...I wanna do an OCD.

Seems like you're already well on your way there!  :icon_mrgreen:

I'm hopefully going to eventually make a generic, good sounding dirt pedal which I can just have on all the time as my default base tone. I feel like I ought to try a lot of different circuits before I settle on one, seeing as I hope to use it all the time for the indefinite future. Other guys would cycle through a dozen pedals until they found one that stayed on their board for years. I intend to breadboard numerous pedals then build my favourite instead of buying and selling loads. Actually come to think of it, guitarists' relationship with dirt pedals sounds kinda similar to marriage. They play the field for a while. They can never quite commit to any one pedal. But then they find "the one" and they never take it off their board. Maybe they still fool around a little on the side but they can never bring themselves to leave "the one".

Other circuits I've considered building but not convinced by: Rat (not fussed). Jackhammer (awesome but complicated and probably too hard clipped to be a good always on pedal). Barber LTD (sounds ok). Bluesbreaker (not a fan but I know they're popular). Sweet honey (nice but sounds a bit fuzzy). Timmy (sounds kinda mediocre to me...).

If no-one can suggest any edits to the nobels circuit I guess I'll just build the whole thing... though I'll probably need a bigger breadboard...

A Wise Man once said: "Give a man a fuzz and he'll jam for a day. Teach a man how to build a fuzz and he'll never jam again." Someone on this forum has or had this as their tag line, I don't remember who, though. All I can say from my experience is that committing to one sound and never wanting to change or improve it is something that only happens to people who don't know which way round to hold a soldering iron. I started with similar ambitions: Just build the "one" bass fuzz that I want and that does not exist and then use that 'till kingdom come. I haven't had a band since and still develop a bunch of ever so slightly different fuzz pedals each year. Taste keeps changing and with each new pedal, new ideas pop up. Doesn't mean you will fall down the same rabbit whole but let me warn you from all of us down here, it is a damn slippery slope.

On a more cheerful note: No point bothering with the BS170's in the OCD. The way the MOSFETs are used here, only the body diodes are active. That means you can replace them with pretty much any silicon diode without an awfully big change in sound, if you adjust C10 accordingly (by ear). Forward biased Zeners will probably be the closest match. If you want to take advantage of the high capacitance of MOSFETs (which to me seems to be the only good reason to use MOSFETs in that configuration), you'll want to use essentially any type of MOSFET *except* 2N7000 or BS170, since those have very low input capacitance values (both 60pF) for a MOSFET. The IRF540 power MOSFET for example has a whopping 1700pF and will give you a much mellower clipping from the body diode. But for the sound you are after, I would suggest BS170 or 2N7000 "used right" (second example on Jack Orman's ever helpful page http://www.muzique.com/lab/zenmos.htm (http://www.muzique.com/lab/zenmos.htm))*[see EDIT below]. This way there really is a big difference in using MOSFETs and the result is very nice and dynamic. Some would call it "tube like", which I don't find helpful but I see where that description is coming from. For this clipping arrangement, I would go to a 18V power supply, else you will only get relatively mild crunch tones before the first opamp stage starts to clip. I would also definitely use an opamp that sounds good when it clips. JFET input opamps such as the TL072, TL082... clip very nastily. The good old NE5532 (BJT input) clips much more musically, my personal favorite for clipping is the NJM2068 (may be hard to come by, though). Rail-to-rail MOSFET opamps such as the TLC2262 are probably the best choice for the sound you seem to be after. Sans amp use them a lot in their amp simulations and simply overdrive the opamps, so that may give you an indication that clipping the right opamp is not a bad thing (whereas clipping the wrong one very much is). With a TLC2262 you'll be limited to <16V supply but since it is rail to rail, and clips nicely it will probably sound good with 9V, too, in an OCD with the "example 2" MOSFET clippers. MOSFET opamps are a bit noisier than good BJT opamps but the TLC2262 is still less noisy than a TL082, so that should not be a massive problem.

Hope that helps,
Andy

EDIT: I forgot to mention that you can also use Schottky diodes with a low forward voltage, such as the 1N5817, to keep the body diodes from engaging. You can do this by adding two 1N5817's to either example 1 or example 2 on Jack's page. Trying to figure out how will be a good mental exercise (plus, I have nothing to draw with me right now). This will lower the clipping threshold by about 0.6V and thus give you a bit more distortion.
Title: Re: Low Gain, neutral dist/OD
Post by: GGBB on October 18, 2019, 03:57:09 PM

The 082 is a lower-noise version of the 072.

Other way around actually. 072 is lower noise version of 082.
Title: Re: Low Gain, neutral dist/OD
Post by: Killthepopular on October 18, 2019, 04:04:48 PM
A Wise Man once said: "Give a man a fuzz and he'll jam for a day. Teach a man how to build a fuzz and he'll never jam again." All I can say from my experience is that committing to one sound and never wanting to change or improve it is something that only happens to people who don't know which way round to hold a soldering iron. Taste keeps changing and with each new pedal, new ideas pop up.

My dad keeps reminding me "it's human nature to never be satisfied with what You've got." Maybe he's right. But on the other hand this is the first time I've gone through a bunch of different circuits to find "my sound". Maybe I will settle on something I'm happy with. I just thought I'd spend some time following it up and see if it looks like a project that has a conclusion or like an abyssal rabbit hole. So far the number of circuits I've tried seems like a reasonable number...

No point bothering with the BS170's in the OCD. The way the MOSFETs are used here, only the body diodes are active. That means you can replace them with pretty much any silicon diode without an awfully big change in sound, if you adjust C10 accordingly (by ear).

Ok. I'll try the bs170s but I'll also try some other diodes (I really like 1n4001). I might try using them "the proper way" too although I already tried that with the electra circuit and I wasn't so keen on the sound.

Rail-to-rail MOSFET opamps such as the TLC2262 are probably the best choice for the sound you seem to be after.

Ok. I'll order some. Presumably they have the same pinout as the tl082? I was also going to mod the son of screamer to sound like a ts9dx. I really like the sound of those other modes (less rolling off of low end, more headroom). I'm assuming that the sound of the ts9 dx comes from the opamp clipping to a large extent. Would the tlc2262 be a good choice there too or should I go for a 4558 if I want the same sound?
Title: Re: Low Gain, neutral dist/OD
Post by: Rob Strand on October 18, 2019, 05:15:20 PM
Quote
So far I've tried 7 different circuits and the only one that actually does what I want is the red llama. I've got another 3 I wanna try. There's the son of screamer which looks pretty straightforward.
I admire your persistence.

Quote
Is there some buffer stuff here that I can leave out?
Only the output buffer.  Don't remove the input buffer, you could replace it with a BJT or opamp buffer if you don't want to use a JFET.    Unfortunately it's not possible to strip that circuit back with having built the whole thing then *you* deciding what you don't need.
Title: Re: Low Gain, neutral dist/OD
Post by: GGBB on October 18, 2019, 07:26:33 PM
Ok. I'll order some. Presumably they have the same pinout as the tl082? I was also going to mod the son of screamer to sound like a ts9dx. I really like the sound of those other modes (less rolling off of low end, more headroom). I'm assuming that the sound of the ts9 dx comes from the opamp clipping to a large extent. Would the tlc2262 be a good choice there too or should I go for a 4558 if I want the same sound?

Keep in mind that input impedance can have a significant impact on overdrives. The TL072/82 and others use JFET input sections to deliver a high input impedance. 4558 and others are BJT based and have lower input impedances. Much like actual JFETs vs BJTs. Fulltone recently updated the OCD and gave it a JFET input buffer to bring Zin up from 330k to 1M. It sounds quite different. That Pedal Show did a comparison very recently - rather long as their videos usually are but very interesting to hear.

So when you are comparing opamps, sometimes the differences you'll be hearing are due to the input impedance of the opamps. It would make sense to be aware of that so that your comparisons are apples-to-apples as much as possible. Note also that you could change the character of any opamp by adjusting input impedance in the circuit. You might find that an opamp you weren't crazy about sounds really good with a bigger or smaller bias resistor or with a JFET buffer in front (or maybe by removing a buffer).
Title: Re: Low Gain, neutral dist/OD
Post by: Killthepopular on October 19, 2019, 05:49:41 AM
Quote
So far I've tried 7 different circuits and the only one that actually does what I want is the red llama. I've got another 3 I wanna try.
I admire your persistence.

Actually tbh the transistor based drives (eighteen, barbershop, peppermill) also pretty much did what I wanted but I didn't care for the sound. Too crispy. I think i prefer the sound of opamps being overdriven.

Don't remove the input buffer, you could replace it with a BJT or opamp buffer if you don't want to use a JFET.

Hm, I really like the sound of the nobels but it's about twice the size of any circuit I've tackled so far... Think I'll shelve it for now.
Title: Re: Low Gain, neutral dist/OD
Post by: Killthepopular on October 19, 2019, 06:32:43 AM

Keep in mind that input impedance can have a significant impact on overdrives. The TL072/82 and others use JFET input sections to deliver a high input impedance. 4558 and others are BJT based and have lower input impedances. Much like actual JFETs vs BJTs. Fulltone recently updated the OCD and gave it a JFET input buffer to bring Zin up from 330k to 1M. It sounds quite different. That Pedal Show did a comparison very recently - rather long as their videos usually are but very interesting to hear.

So when you are comparing opamps, sometimes the differences you'll be hearing are due to the input impedance of the opamps. It would make sense to be aware of that so that your comparisons are apples-to-apples as much as possible. Note also that you could change the character of any opamp by adjusting input impedance in the circuit. You might find that an opamp you weren't crazy about sounds really good with a bigger or smaller bias resistor or with a JFET buffer in front (or maybe by removing a buffer).

Yeah I saw that episode the other day. There was a big difference in the amount of high frequences in the two OCDs.

I guess I'll just stick with my tl072s for now and maybe try tinkering with input impedance once I get the circuit running.
Title: Re: Low Gain, neutral dist/OD
Post by: Ben N on October 19, 2019, 04:08:20 PM
I'm hopefully going to eventually make a generic, good sounding dirt pedal which I can just have on all the time as my default base tone. I feel like I ought to try a lot of different circuits before I settle on one, seeing as I hope to use it all the time for the indefinite future.
You're not wrong, even if this quest can be a little maddening, and even a little self-defeating. I'm on a similar quest--even if without quite the same programmatic focus and persistence. Given the range of drives you've tried, in terms of gain and eq, it's hard to know what you're really after, but in my experience only three have ever scratched that particular itch, a DOD FX-50 (the one without the tone control), an MXR Distortion III, and, the current choice, a near-clone of the Nobels ODR-1 that I built on the Aion Andromeda PCB. I really like the ODR-1. While I'm sure it's not for everyone, it's worth checking out. Past failed candidates have included an OCD clone, Boss BD-2 and OD-3, and a Barber Direct Drive. Like you said, I didn't connect with the Timmy in this application, but I find it useful for stacking and boosting, or alternating more of a mid-focussed sound with the ODR-1.
Title: Re: Low Gain, neutral dist/OD
Post by: Killthepopular on October 24, 2019, 11:34:19 AM
I'm becoming interested in the idea of adding a TMB tonestack. It's effectively an "amp emulator" that i want to build, partly to be used in conjunction with my cab sim pedal. Seems like adding a proper amp tone stack would make sense... Would this be fairly easy to do? What would the downsides be? I understand that there will be an output level drop but with a circuit like the red llama which seems to have a crazy amount of output I assume this wouldn't be a big issue.

Apparently tone stacks tend to always cut a bit of mids so presumably this might mean that using a pedal with a tone stack into a standard amp with a tone stack could result in an overly scooped sound? OTOH a lot of people seem to think the guvnor sounds great going into the front of an amp so maybe it's not such a big deal. Perhaps a wise move would be to include a switch to bypass the tonestack...


(https://i.postimg.cc/Z0ZMd4dJ/Way-Huge-Red-Llama-Schematic.png) (https://postimg.cc/Z0ZMd4dJ)

Would it be as simple as replacing the 10uf cap with the marshall tone stack from the duncan amps tone stack calculator?
Title: Re: not so Low Gain, not really neutral dist/OD
Post by: GGBB on October 25, 2019, 06:31:30 PM
Not really all that "low gain" - and now no longer neutral. ;)

A good tone stack might be trickier than just a tack on. These too are affected by surrounding impedances, so the traditional stacks are designed around specific Zin and Zout characteristics found in their respective amp stages. So some adjustment and tweaking will probably be in order. Amp-in-a-box has been done many times in many ways so there are plenty of examples out there to learn from.
Title: Re: not so Low Gain, not really neutral dist/OD
Post by: Killthepopular on October 26, 2019, 07:02:43 AM
Not really all that "low gain" - and now no longer neutral. ;)

A good tone stack might be trickier than just a tack on. These too are affected by surrounding impedances, so the traditional stacks are designed around specific Zin and Zout characteristics found in their respective amp stages. So some adjustment and tweaking will probably be in order. Amp-in-a-box has been done many times in many ways so there are plenty of examples out there to learn from.

Is the impedance the resistance between the first and last component of a circuit when Measured with a multimeter? Or rather, the resistance between the input and output?
Title: Re: Low Gain, neutral dist/OD
Post by: GGBB on October 26, 2019, 12:23:55 PM
Is the impedance the resistance between the first and last component of a circuit when Measured with a multimeter? Or rather, the resistance between the input and output?

Not exactly, but resistance is part of it I think. Impedance (Z) is a little above my pay grade, so I'll tell you how I understand it. Z is related to both resistance and reactance (which relates to phase). In our case we're concerned with audio frequency AC - so a simple DC measurement of resistance is not the same thing at all. Anywhere you have resistance, capacitance and inductance you have an AC filter of some sort, which creates reactance thereby affecting Z. Tacking a filter - which has a certain Z - after or before some other Z, changes the result of the individual pieces. We often refer to that kind of thing as loading. In audio we use high Zin and low Zout buffers when we want to minimize loading effects.
Title: Re: Low Gain, neutral dist/OD
Post by: Fancy Lime on October 26, 2019, 04:25:21 PM
Impedance is too complex a concept to give generalized answers that are still useful in a concrete application. It does indeed have to do with resistance, reactance and phase. Fortunately, for our little diystompbox problems  we usually only need to concern ourselves with the sum of resistance and reactance. Resistance is the (frequency independent) resistance to a DC or AC signal (well, duh!), reactance is the frequency dependent resistance to an AC signal. Since audio is always AC, the sum of the two is also simply a frequency dependent resistance, for all we care (most of the time).

Output impedance of a circuit is the frequency dependent resistance that follows the last active component of the circuit in series until the output jack. In a real-world circuit that includes the output impedance of the last active device itself but this is often (not always!) small enough to be ignored.

Input resistance is the frequency dependent resistance to "ground" before the first active component. Beware, though, that "ground" in this case means "any and all reference voltages", including things like the virtual ground point of an inverter input. It also contains contributions from the active device itself that depend on the circuit topology and the device used. Luckily, there are equations for all reasonably common topologies and many uncommon or downright bizarre topologies to be found on the great interwebs. And most of them can be simplified dramatically without introducing too much additional errors. For example, for a non-inverting opamp, you can say "the input impedance is the total DC resistance to ground before the input", and that is wrong bit it is "correct enough" for most things where we care about impedance.

The "total impedance of a circuit" does not generally exist, especially for active circuits. So hooking a multimeter to both ends of a stompbox is not going to tell you anything about the impedance.

But for your design problem, I think the whole impedance discussion will not be super useful without much, much more other background. And learning theory is not as much fun as building a working pedal for most people, or so I'm told.

So my recommendation to you would be to try the following: You like the Red Llama (or your modded version of it), right? Take that circuit up to and including C6. Leave out the Vol pot. Add another inverter stage with a 100k pot wired as a series resistor before the inverter input and a 100k resistor in the negative feedback loop. This is now a buffered Volume control. Next add another stage with one more inverter, which you use as a 2-band Baxandall tone stack. This is the most useful tone stack topology in my personal opinion. Very flexible and easy to use. Banxanwhat? This:
http://www.learnabout-electronics.org/Downloads/NegativeFeedbackTone.pdf
I hope I find the time to draw the whole thing for you tomorrow, but I am a bit short on time this weekend, so it may be a few more days. Unless someone beats me to it. I've been meaning to build something like that anyway, just did not find the time.

Hope that helps,
Andy
Title: Re: Low Gain, neutral dist/OD
Post by: PRR on October 26, 2019, 05:43:49 PM
> Is the impedance the resistance between the first and last component of a circuit when Measured with a multimeter?

It isn't, but would be, IF you replaced the DC battery in the meter with an audio source (variable frequency because impedance often varies with frequency) and replaced the DC meter with an AC/Audio meter.

There have been audio impedance testers with 50Hz/1KHz/5kHz to cover 10-1k Ohms (the most likely values in large PA systems). Here's a $150 job which only tests 1kHz.
https://www.amazon.com/d/Multi-Testers/Tenma-72-6948-Audio-Impedance-Meter/B008BW9MI0
$700 with more settings (but does not sense high ohms):
https://www.amazon.com/Gold-Line-ZM-1P-Impedance-Protection/dp/B0006TZ4UG

Generally you rig a signal generator, variable resistor, and audio voltmeter and do math.

A super-simple trick for guitar levels is to put a 0-500k pot in series with an input. Trim the pot up from zero until it is "half loud", then measure the pot. But what happens on many guitar inputs is the bass and treble don't fade-out equally-- which matters more? It Depends.
Title: Re: Low Gain, neutral dist/OD
Post by: Fancy Lime on October 29, 2019, 05:31:48 PM
Hi folks!

So here is the "Baxandllama" I've been promising, finally:

(https://i.postimg.cc/Yvh9LyGR/Infrared-Llama.png) (https://postimg.cc/Yvh9LyGR)

The inverters should of course be CD4069UBE or CD4049, I just did't have the right symbol at hand. The EQ gives you + or - 12dB at 100Hz and 6kHz. This is not tested, not even on the breadboard, just simulated. So take this as a starting point and tune from there by ear. Best to start by playing around with the values of C7 and C8. Also, it may be wise to add Capacitors in the 500p to 1n range in parallel with R6 and R12 to cut the hiss. The first 2 inverters are just the standard Llama values, so replace that with your favorite values.

Cheers,
Andy
Title: Re: Low Gain, neutral dist/OD
Post by: Killthepopular on November 08, 2019, 06:35:38 AM
If I'm using a cd4049 how can I tell which pin is which on the baxandllama? The Red LLama schematic I used had the pins numbered 1-16, which I understand.

I'll be intrigued to see what it sounds like. I have a sneaking suspicion that it might actually sound quite different from the red llama.

Also, where does the 9V enter the circuit? I can't see it on here.

And does it matter that there's only 2 points connected to ground? I'm just used to there being more ground connections in these circuits is all...
Title: Re: Low Gain, neutral dist/OD
Post by: Fancy Lime on November 08, 2019, 01:42:43 PM
No time right now, so real quick: google "cd4049" and look at the datasheet. It contains the info you are searching. I'll try to be more helpful soon.
Andy
Title: Re: Low Gain, neutral dist/OD
Post by: Kipper4 on November 08, 2019, 02:12:59 PM

(https://i.postimg.cc/crgSVXHf/IMG-1590.png) (https://postimg.cc/crgSVXHf)

Not the data sheet but a pinout diagram. Which should clear up a few questions.
Pin1 Vdd will be your plus rail voltage.
Pin8 Vss will be ground
Like I say I haven't googled the sheet.

The plus rail and ground will be common to all the inverters in the package.

The diagram is handy in that it gives you a sense of the inputs and outputs.

Not sure where you're up to and no offence but if you were looking at an inverter circuit like this when your used to seeing maybe tube screamers. You'd wonder where's all the non inverting inputs and how are they biasing the chip.

So the circuit is an gain stage. That's gonna distort like mad if dimed.

LPF

Another gain stage.

Active tone stack.

Hope I'm not interfering.
Title: Re: Low Gain, neutral dist/OD
Post by: Killthepopular on November 09, 2019, 04:50:27 PM
FWIW, here's a way to add a control to the DOD 250.


(https://i.postimg.cc/GHb85TcP/Simple-DOD250-Tone-Control-V1-1.png) (https://postimg.cc/GHb85TcP)

What does C5 NF mean?
Title: Re: Low Gain, neutral dist/OD
Post by: bluebunny on November 10, 2019, 07:34:02 AM
What does C5 NF mean?

On the rare occasions I've seen this, it's meant "not fitted".  So ignore it.  Not sure of the value of this notation, but perhaps there were variations of this circuit where this particular cap was indeed present?
Title: Re: Low Gain, neutral dist/OD
Post by: Killthepopular on November 11, 2019, 10:26:15 AM
Currently fooling around with a 250, just a standard schematic, not the tone control one. Comparing it to the vox distortion I'm struck by 2 things. 1, it seems kinda lower gain to me. 2, I'm shocked by how much it just sounds like a treble booster. When I turn up to max gain it's like the overall sound doesn't get that much louder but the trebles seem to get boosted. It's possible that I've messed up the schematic a bit but I have heard that 250s are kinda like treble boosters so I'm guessing this is right.

(https://i.postimg.cc/hfM9xjLQ/DOD-250-Overdrive-Schematic.png) (https://postimg.cc/hfM9xjLQ)

What the function of C5? With the gain set to minimum the tone is really dull and really bright when set to high. Increasing C5 makes the tone duller which is good for high gain but it makes the low gain sounds even more unusable.

Why the big difference between high and low gain tones? Is the gain pot partially acting as a high pass filter?
Title: Re: Low Gain, neutral dist/OD
Post by: Killthepopular on November 11, 2019, 01:07:29 PM
How do I add a high pass control to this circuit? I've done the low pass thing. The signal goes through a pot and then past a cap that goes to ground. Simple. 2 Components. But when I try to do the same thing with a high pass filter I just create a sort of volume control. The signal goes through a cap this time and then past a pot that's connected to ground but as I turn the pot I end up just sending the entire signal to ground.
I can't get my head around how it's supposed to be wired. How do you wire up a high pass control? Is it not possible to do it without a bunch of extra components? I understand how a HPF should be wired, I just don't understand how you can subsitute a pot for the resistor without just turning it into a volume control.
I'm just playing around here, experimenting. I might try a big muff style tone stack instead.
Title: Re: Low Gain, neutral dist/OD
Post by: GGBB on November 12, 2019, 12:07:23 AM
How do I add a high pass control to this circuit? I've done the low pass thing. The signal goes through a pot and then past a cap that goes to ground. Simple. 2 Components. But when I try to do the same thing with a high pass filter I just create a sort of volume control. The signal goes through a cap this time and then past a pot that's connected to ground but as I turn the pot I end up just sending the entire signal to ground.
I can't get my head around how it's supposed to be wired. How do you wire up a high pass control? Is it not possible to do it without a bunch of extra components? I understand how a HPF should be wired, I just don't understand how you can subsitute a pot for the resistor without just turning it into a volume control.
I'm just playing around here, experimenting. I might try a big muff style tone stack instead.

Use a 10k pot in place of R9 or R6 - connected at pins 1 and 3. Then add a cap from the wiper to one end. You'll have to experiment with the cap value, and you may want to use a fixed resistor in series with the pot to set the filter limit. See the second image here: http://www.muzique.com/lab/swtc.htm.
Title: Re: Low Gain, neutral dist/OD
Post by: Killthepopular on November 14, 2019, 08:12:10 AM

Use a 10k pot in place of R9 or R6 - connected at pins 1 and 3. Then add a cap from the wiper to one end. You'll have to experiment with the cap value, and you may want to use a fixed resistor in series with the pot to set the filter limit. See the second image here: http://www.muzique.com/lab/swtc.htm.

I couldn't get that circuit to work but I tried the one below it (3rd picture) and it works great although I can't get enough hi boost from it. How would I increase the amount of hi boost?

The DOD 250 is now the 8th circuit I've tried and it's the first one so far that really feels like THE SOUND. I'm inclined to stop trying out different circuits and instead stick with this one but tinker with it to get it to do what I want.


(https://i.postimg.cc/hXK277Zd/DOD-250-Overdrive-Schematic.png) (https://postimg.cc/hXK277Zd)

I've got a 1n4001 vs 2 x 1n34a as my clipping diodes. How do I reduce the minimum amount of gain without reducing the maximum gain? I 've swapped the 500k pot for a 1m. Is that the right way?

I might want to add a post tone control boost as well as the current max output level at low gain is a bit below my guitar at full volume.
Title: Re: Low Gain, neutral dist/OD
Post by: duck_arse on November 14, 2019, 08:31:11 AM
I'm the worst person on earth to ask/tell about tone controls, but this top-cut is what I put on my recent distortion + build. it works ok, could almost be called a bass control.
(https://i.imgur.com/8nQTCsb.png)

the more I look at my diagram, the more I'm sure I've connected it wrong, but that is how it was tested and built.

to get less minimum gain on your dod, you need to match the gain pot value to the feedback resistor value. you will never get less than a gain of 2, tho, I thimk.

[edit :] deleted
Title: Re: Low Gain, neutral dist/OD
Post by: GGBB on November 14, 2019, 08:40:56 AM

Use a 10k pot in place of R9 or R6 - connected at pins 1 and 3. Then add a cap from the wiper to one end. You'll have to experiment with the cap value, and you may want to use a fixed resistor in series with the pot to set the filter limit. See the second image here: http://www.muzique.com/lab/swtc.htm.

I couldn't get that circuit to work but I tried the one below it (3rd picture) and it works great although I can't get enough hi boost from it. How would I increase the amount of hi boost?

Any one or a combination of: bigger C1, smaller R1, bigger R2, smaller Tone pot.
Title: Re: Low Gain, neutral dist/OD
Post by: Kipper4 on November 14, 2019, 08:59:50 AM
You'd be better off starting a new how  to mod my dod 250 thread of your own.
Meantime heres some reading that will help further your learning about op amp gain and filters

http://www.generalguitargadgets.com/how-to-build-it/technical-help/articles/design-distortion/
Title: Re: Low Gain, neutral dist/OD
Post by: PBE6 on November 14, 2019, 10:19:56 AM
Comparing it to the vox distortion I'm struck by 2 things. 1, it seems kinda lower gain to me. 2, I'm shocked by how much it just sounds like a treble booster. When I turn up to max gain it's like the overall sound doesn't get that much louder but the trebles seem to get boosted.

Why the big difference between high and low gain tones? Is the gain pot partially acting as a high pass filter?

Your observations are all related.  Many non-inverting opamp distortion circuits have two simple filters, a low-cut and a high-cut.  In this case, the combination of C3 and R7+VR1 act as the low-cut filter, with a frequency that varies between 1/(2*pi*C3*R7) = 63 Hz at minimum gain and 1/(2*pi*C3*(R7+VR1)) = 7.2 kHz at maximum gain.  The higher the gain the less bass content there is in the signal, hence the impression of a treble boost.  Coupled with that, less bass content means fewer mid-range and high-end harmonics are formed when clipping the signal and so the character of the distortion is less muddy, hence the impression that it doesn't have as much gain as other fuzzier pedals that retain more bass content.  (As a side note, if you want more bass but like the character of bass-light clipping, you can add a clean bass boost after the clipping stage.)

What the function of C5? With the gain set to minimum the tone is really dull and really bright when set to high. Increasing C5 makes the tone duller which is good for high gain but it makes the low gain sounds even more unusable.

This is the high-cut filter, which is formed by C5 and R8 and has a frequency of 1/(2*pi*C5*R8) = 7.2 kHz, and it has the effect of minimizing the shrill high-end harmonics generated during clipping.  Increasing the value of C5 will lower the frequency of the filter, making things more mellow or more dull depending on your preference.  If you notice, the low-cut and high-cut filters are almost the same when the gain is all the way up which creates a very trebley 7.2 kHz-focused sound.  (Tubescreamers do this too, but the emphasized region is wider and starts much lower, around 720 Hz.)  You may want to play around with the filters to fine tune where this emphasis will be when the gain is cranked.
Title: Re: Low Gain, neutral dist/OD
Post by: Fancy Lime on November 16, 2019, 07:30:49 AM
A few answers about the Baxandallama, finally:

@Killthepolular:
With the tone controls on 12 o'clock, the Baxandallama should sound very similar to the normal Llama. The 3rd and 4th stage do not perform any tone shaping unless the knobs are turned. At high volume settings these stages may clip but that will make very little difference after the first two massively clipping stages. Anyway, it is worth tinkering with the first two stages to reduce gain (as we discussed in this thread earlier).
CMOS inverters need no referencing to ground or any other reference voltage (which may in turn be connected to ground) because they are biased via the resistor between the output and input of each inverter (R3 + Gain, R4, R6, R12). This type of biasing is known as "virtual ground" biasing because the inverter itself just makes it's own "ground" right in the middle of V+ and V- (where V- is usually the "external ground"). Try to think about what happens when the input of the inverter swings high and what happens when it swings low. What will the output of the inverter do? And if input and output are DC coupled via a resistor, what does that mean for the DC voltage at the input when there is no signal coming in?

@Kipper4
Hi Rich, well, the point of having the volume control setup the way it is, incorporated in stage 3, which has a gin between 0 and 1, is to be able to use an active one stack without overloading it completely. Unless you want to. In fact, having a boosted bass band clip a CMOS inverter gently, sounds rather pleasant. But if you do that, you get almost 9V of signal swing at the output of this thing. And if that is something the user wants is, uhm, questionable. But a second volume control (master) at the end would fix that.

Cheers,
Andy
Title: Re: Low Gain, neutral dist/OD
Post by: Killthepopular on December 05, 2019, 06:57:35 AM
I had a listen back to all the clips I've recorded of the 8 circuits I've tried and now I'm thinking that the electra is my favourite. Here's a summary of the 8 circuits:

Electra: Surprisingly good. I like the compression. Generally pleasant, smooth, well balanced tone. Seems to have a good gain range and can do low and high gain stuff equally well.
Llama: Very good at that Tubey, fendery sound of making everything sound just slightly overdriven all the time. It's a bit too transparent though, or too dynamic. It lets some harshness or twanginess of the guitar leak through where a more aggressive clipping circuit would turn it all to mush and make things easier on the ear. I also get a bit frustrated when i turn up the gain and don't get much more out of it.
Vox distortion: rubbish at low gain. Sounds badass but can get a bit harsh.
Peppermill: sounds outright bad but can be surprisingly good at low gain stuff.
Barbershop: Generally sounds decent but it's not one of my favourites.
Eighteen: Mostly sounds good but it can be a bit nasty. Not great at low gain.
Dod250: Rubbish at low gain. I don't like the way it's really thin and bright at max gain and totally muffled at minimum gain. Would require me to make a really good tone circuit to go with it and I'd need to fiddle with it every time i touched the gain knob.

I'm starting to get a sense of the difference between "feel" and "tone". The dod250 makes me feel like a rockstar. It's so awesome to play but when i listen objectively i find it to be very poorly balanced and unnatural. The llama on the other hand is one of the better sounding circuits but I find it a bit boring to play for some reason.

I ended up buying parts for several more circuits I wanna try. There were a few circuits that just had way too much praise on The Gear Page so I felt like i had to try them out. I'll make the following circuits soon: Son of screamer. Baxandllama. Rat. Timmy. OCD. Barber LTD silver.

I also got the parts for an ep booster which i'll try out once I've got my main dirt circuit sorted.
Title: Re: Low Gain, neutral dist/OD
Post by: Mark Hammer on December 05, 2019, 07:22:28 AM
Dod250: Rubbish at low gain. I don't like the way it's really thin and bright at max gain and totally muffled at minimum gain. Would require me to make a really good tone circuit to go with it and I'd need to fiddle with it every time i touched the gain knob.

I'm starting to get a sense of the difference between "feel" and "tone". The dod250 makes me feel like a rockstar. It's so awesome to play but when i listen objectively i find it to be very poorly balanced and unnatural. The llama on the other hand is one of the better sounding circuits but I find it a bit boring to play for some reason.
The 250 and its sibling, the MXR Distortion+, use changes to the ground leg resistance to alter gain, rather than the feedback resistance, as the Tube Screamer does.  You can do the math but dropping the ground leg resistance to increment gain always moves the bass rolloff upwards, while increasing the feedback resistance to increment gain always moves the treble rolloff downwards.  Whether either of those gain-changes results in audible changes in tone depends on the value of the capacitors used in each respective arrangement.  The ground-leg cap used in the 250 is 47nf (.047uf).  At min gain the rolloff is inaudible, but at max gain the bass rolloff begins at 720hz, resulting in the thin sound.  And in the absence of any useful treble-cut anywhere else in the circuit, that gets really shrill.

To "fix" it, replace the 47nf cap with 220nf, stick a 68-100pf cap in parallel with the 1meg feedback resistor, and replace the 1000pf cap in parallel with the clipping diodes with a 2700-3300pf cap.  Those changes will sand down the sharp edges more, and deliver more oomph at higher gain.  One of the side-effects of retaining more bass in the "drive" stage, prior to the clipping diodes, will be that overdrive is achieved a little more easily, since retaining bass will increase overall amplitude.
Title: Re: Low Gain, neutral dist/OD
Post by: Fancy Lime on December 05, 2019, 04:54:57 PM
Dod250: Rubbish at low gain. I don't like the way it's really thin and bright at max gain and totally muffled at minimum gain. Would require me to make a really good tone circuit to go with it and I'd need to fiddle with it every time i touched the gain knob.

I'm starting to get a sense of the difference between "feel" and "tone". The dod250 makes me feel like a rockstar. It's so awesome to play but when i listen objectively i find it to be very poorly balanced and unnatural. The llama on the other hand is one of the better sounding circuits but I find it a bit boring to play for some reason.
The 250 and its sibling, the MXR Distortion+, use changes to the ground leg resistance to alter gain, rather than the feedback resistance, as the Tube Screamer does.  You can do the math but dropping the ground leg resistance to increment gain always moves the bass rolloff upwards, while increasing the feedback resistance to increment gain always moves the treble rolloff downwards.  Whether either of those gain-changes results in audible changes in tone depends on the value of the capacitors used in each respective arrangement.  The ground-leg cap used in the 250 is 47nf (.047uf).  At min gain the rolloff is inaudible, but at max gain the bass rolloff begins at 720hz, resulting in the thin sound.  And in the absence of any useful treble-cut anywhere else in the circuit, that gets really shrill.

To "fix" it, replace the 47nf cap with 220nf, stick a 68-100pf cap in parallel with the 1meg feedback resistor, and replace the 1000pf cap in parallel with the clipping diodes with a 2700-3300pf cap.  Those changes will sand down the sharp edges more, and deliver more oomph at higher gain.  One of the side-effects of retaining more bass in the "drive" stage, prior to the clipping diodes, will be that overdrive is achieved a little more easily, since retaining bass will increase overall amplitude.

The "treble boosting" effect of a pot in the ground leg and the "bass boosting" effect of a pot in the feedback leg of a non-inverting opamp can also be used deliberately for extra flexibility. I just happen to have an overdrive circuit on the breadboard right now that does exactly that. A 500k pot in the feedback loop provides the overall gain and has a 1n cap in parallel. There are two ground legs. One is just a 2k2 resistor and a 3u3 cap for full range response down to 21Hz. In parallel with that is a 470R, 100n leg with a 5k pot in series. This pot now acts like a variable treble booster or a Presence pot. Very useful and flexible combination, definitely worth the extra pot in my oppinion.

The thing on my bradboard is a kind of multi-drive. Very simple design but goes from clean boost through blues-driver territory to high gain metal distortion or fuzz, depending on just a vew options. A few of the possible incarnations may be of interest to you. My favourite low gain, natural overdrive variant relies on opamp clipping from a NJM2068. Yes, I am an absolute NJM2068 fanboy, and I don't care who knows it. These are a bit hard to come by though. I highly recommend you get some if you can, their clipping is by far my favourite opamp clipping. Very Blues Driver like, to my ears at least. A NE5532 works too and sounds amazing with bass in this circuit but not quite as good as the NJM2068 with guitar. However, MOSFETs as clipping diodes make the NE5532 variant into a great tubey drive. Enough teasing, I hope I'll get the drawings of the circuit done tomorrow or on the weekend at the latest. If i don't get the full shebang with all options done, I'll try to at least get the low gain bluesy thing (which is the simplest variant anyway) out the door.

Cheers,
Andy
Title: Re: Low Gain, neutral dist/OD
Post by: Mark Hammer on December 05, 2019, 09:27:56 PM
That "Rat trick" (2nd ground leg) is handy, innit?
Title: Re: Low Gain, neutral dist/OD
Post by: Fancy Lime on December 06, 2019, 09:53:14 AM
That "Rat trick" (2nd ground leg) is handy, innit?
Yepp, sure is, especially with one of the legs being variable.

BTW, here is what I went on about yesterday:
https://www.diystompboxes.com/smfforum/index.php?topic=123516.0

Cheers,
Andy
Title: Re: Low Gain, neutral dist/OD
Post by: Killthepopular on December 21, 2019, 06:35:06 PM
I think I'll put my 2 favourite circuits together in a box so I can have one or the other or stack them. Currently my 2 favorite circuits are the red llama and the electra. The reason is that the main premise for this project was to make an amp like drive, one that didn't cut bass and had a nice natural (not crackly) low gain sound, and those 2 circuits seem to fulfill those requirements better than the other circuits I've tried. I recently built (breadboard) the son of screamer, rat, OCD and the timmy. I liked all of them but I found that they all cut a lot of bass in that typical overdrive way and didn't sound as full as the electra or red llama. I also don't really like the clean blend sound you get from these tube screamer style pedals. I was going to do the barber Ltd next. Is it worth bothering with or will I not like it if I didn't like the tube screamer and timmy?
Title: Re: Low Gain, neutral dist/OD
Post by: roseblood11 on December 21, 2019, 06:44:56 PM
Suggestion for the bypass switching:
https://forum.pedalpcb.com/threads/two-fx-toggle-flex-relay-switching.499/

PS: I had this idea of putting my "two favourite" overdrive/distortion pedals in one box many years ago. It NEVER ends. You'll always find another two circuits that look promising.  :icon_mrgreen:
Title: Re: Low Gain, neutral dist/OD
Post by: Killthepopular on December 22, 2019, 03:23:13 AM
I quite like Joe Davisson's EZ-250.  Only 15 parts (+ pots).  Links for: thread (https://www.diystompboxes.com/smfforum/index.php?topic=103671.0), schematic (http://www.bouron.org.uk/marc/ez250.jpg), my layout (http://www.bouron.org.uk/marc/EZ250B.GIF).

Seeing as my fave circuit so far is a transistor boost followed by diodes clipping to ground I thought I ought to try this one out. J201, 2n5088, bs170, 2n3904, 2n2222, vp3203. Those are my transistors. Which should I use? I might also try modding an lpb1 as I like the sound of it.
Title: Re: Low Gain, neutral dist/OD
Post by: Killthepopular on December 22, 2019, 07:52:01 AM
OK, just built the ez 250 using a 5k gain pot and 2n5088s. I like it. What's the difference between this and the electra? I find it still sounds pretty good when I max the gain and hit it with a boosted signal whereas the electra would sound like crap, just a totally farty, saggy transistor sound. What's the difference there? Is it the different transistor i'm using (2n3904 on the electra)? Is it something in the design of the circuit (two transistors rather than just one)? Or did i perhaps just not set up my electra correctly?
Title: Re: Low Gain, neutral dist/OD
Post by: Elijah-Baley on December 22, 2019, 08:16:51 AM
I didn't find any video or audio demo of the EZ 250. (I'm searching a tiny distortion circuit to fit in a 1590A box).
Title: Re: Low Gain, neutral dist/OD
Post by: bluebunny on December 22, 2019, 04:20:26 PM
I didn't find any video or audio demo of the EZ 250. (I'm searching a tiny distortion circuit to fit in a 1590A box).

I can't recall Joe doing a demo.  It certainly fits in a 1590A.
Title: Re: Low Gain, neutral dist/OD
Post by: Killthepopular on December 22, 2019, 05:53:58 PM
I didn't find any video or audio demo of the EZ 250. (I'm searching a tiny distortion circuit to fit in a 1590A box).

My demo of the EZ-250: https://youtu.be/7SJKp7w4u28

This was the 13th dirt circuit I've breadboarded for this project so far. It's not got as much low end and top end as the llama and the electra but it is also not as mid-focussed as the tubescreamer, timmy, OCD or rat. It sounds good at low gain to my ears. I used 2n5088 and 1n34a and 1n4001 diodes.

I think it has bumped the llama off the #2 spot. It doesn't sound as badass as the electra but I think it is probably a classier sound, smoother but still well balanced. Llama is very good but it lets through some harsh tones sometimes and the lack of high gain is disappointing. Electra is still my fave and this is #2, so currently my finished pedal would be electra into ez-250. I'd probably also add a diode lift to both circuits so i could use either one as a boost too.

I ought to have a look at more transistor with diodes clipping to ground type circuits. Transistor fuzz/overdrive sounds too bright and crackly to me. Opamp distortions and overdrives all seem to cut too much bass or sound no good at low gain. Transistor plus diode distortions seem to be some of the rare circuits that have a fairly natural sounding grit and don't cut bass.
Title: Re: Low Gain, neutral dist/OD
Post by: Elijah-Baley on December 23, 2019, 05:06:30 AM
I like it. I could try it, it could be my overdrive 1590A.
I hope it's not too harsh, nor poor low end, and it will sound nice at high gain setting. Actually I prefer something a bit more more aggressive.
Maybe is not the right place, but how I can make it more gainy?
Title: Re: Low Gain, neutral dist/OD
Post by: Fancy Lime on December 25, 2019, 03:49:40 PM
@Killthepopular

You aren't going to be satisfied until you tested *all* the overdrives, are you? May I suggest you call the pedal that will hopefully someday be the result of your labors "The Stickler"? I mean that in the most endearing sense of the word.
One thing that strikes me about your recent posts in this thread is, that you seem to know pretty well by now what you like sound-wise but not really how a schematic translates to sound. For example, you say that the Son of Screamer, OCD, Timmy, and Rat all cut bass and that that is what you disliked about them. You can change that bass cut (which is actually a mid or treble boost, but same difference) very easily by changing just a few component values. I think it is time you started designing your very own overdrive, starting at one of those that you like *pretty much* and changing the aspects that are not 100% on the nose for you. I think this may ultimately get you closer to the sound in your head than trying lots of existing designs, many of which are, fundamentally, very similar. Tell us what you want as precisely as you can in relation to the designs you have tried, and we'll be glad to help you figure out what to tinker with. If I understand you correctly, you want:
1. Flat frequency response
2. Hard clipping with smooth transition into clipping
3. Low to medium gain
Right? Anything else? What designs tick which boxes for you?


I like it. I could try it, it could be my overdrive 1590A.
I hope it's not too harsh, nor poor low end, and it will sound nice at high gain setting. Actually I prefer something a bit more more aggressive.
Maybe is not the right place, but how I can make it more gainy?
More gainy? Bootstrapping! Inspired by this thread, I started tinkering with a dual-boostrapped version of the EZ-250. The first transistor is bootstrapped for higher input impedance and the second one for higher gain. I'm still polishing the component values but so far I'm pretty happy with where it is going, namely a higher gain EZ-250. One could of course just properly redesign a DOD 250 with a modern opamp instead and get even more gain, lower noise, less parts... But where's the fun in that? Discreet transistor designs still have that certain je ne sais quoi, don't they?

Cheers,
Andy
Title: Re: Low Gain, neutral dist/OD
Post by: Fancy Lime on December 26, 2019, 05:32:29 PM
Here you go, a higher gain EZ-250:

https://www.diystompboxes.com/smfforum/index.php?topic=123610.0

Andy
Title: Re: Low Gain, neutral dist/OD
Post by: Killthepopular on December 30, 2019, 08:37:11 AM
1. Flat frequency response
2. Hard clipping with smooth transition into clipping
3. Low to medium gain
Right? Anything else? What designs tick which boxes for you?

Thanks for all the help Andy. I was going to start trying variations on the electra (folk driver, english gent, clock of tone, ghetto stomp) and the red llama (tube sound fuzz, Double D) but your approach is probably the more correct one.

1. Flat frequency response: Yes. However, I also probably want a switch or pot to roll off the low end when I want to i.e. playing with a bassist. I would also add "consistency" to this requirement. I'd like a circuit that sounds well balanced at all gain settings or at least has a good tone control that can counter any imbalances. The variation in tone in the dod 250 (really dull at minimum gain, no low end at max gain) makes it unuseable. Most circuits have consistency although some transistor based things seem to get a bit too edgy at high gain. Many circuits don't have a flat response. I've tried letting more bass into the tube screamer design and this just seems to make things too muddy but still quite thin.
2. Hard clipping: Maybe. Probably. Smooth transition into clipping: Yes. Electra style circuits seem to be quite smooth. Tube screamer things are good but they have too much clean signal mixed in. Llama is very good. Overloaded opamps are cool but not good at smooth clipping. Vox and dod were bad at low gain. Rat and OCD were pretty good but still not as good as llama and electra. I find that asymmetrical clipping diodes help with this as the sweet spot is easier to find when you are only clipping one side of the wave instead of both.
3. Low to medium gain: Yes, although a circuit that can get into high gain too would be a big plus. Llama is the only circuit that had a really narrow gain range.

Those are probably the main things but there's a few more things I've picked up:

4. I like a circuit that's not too transparent. For me the Llama and tube screamer seem to emphasise or let through the natural twanginess of my high strings which sounds ugly. Circuits like the electra and the rat seem to turn the signal to mush, even at low gain, in a way that's pleasing to the ear.
5. I just find some circuits more exciting than others. The llama ticks lots of boxes but feels a bit boring. It was the only circuit which stood out as feeling a bit boring. The dod 250, rat and vox distortion tick hardly any boxes but they feel more exciting than most other circuits.
6. Warmth. That thing where people describe transistors as warm, buttery and musical and opamps as cold and sterile, I can hear that a little bit. The clipping and the overall tone of transistor circuits can sometimes be ugly but there does seem to be something in the feel that's a bit more sweet and glassy somehow. Opamp circuits can have their own nice tone but transistor circuits almost seem to make my guitar sound like a better guitar. I guess it's like, the sound of the distortion is one thing, but when it comes to being fairly clean, transistors seem to improve the overall tone.
7. It might be nice for it to take a really hot input. I might want to boost into it some time for a really high gain sound. It often seems to me that transistors don't like being hit with too much gain but opamps can handle it better. That might just be my limited experience.

Maybe I could have 3 sections, each with a bypass switch. A: transistor boost with gain and volume pots. B: Opamp Boost with gain and volume. C: Diodes with master volume and low cut switch. A and B could be footswitchable so I could use one as always on and one as a boost for more gain. Section C could just have a finger switch as its not the sort of section you would turn on and off during a song. Having bypassable diodes means I could just use the rest of the pedal as a boost or fuzz. Having a separate gain and vol for each section means I could control exactly how much clipping each section is doing.
Title: Re: Low Gain, neutral dist/OD
Post by: marcelomd on December 30, 2019, 10:57:37 AM
Hi,

Suggestion: Try the Blackstone Appliances MOSFET overdrive. At its core it's a CMOS inverter overdrive, like the llama with some tone shaping. Looks like a quick build.

Schematic: http://fuzzypedals.blogspot.com/2015/06/blackstone-mosfet-overdrive.html (http://fuzzypedals.blogspot.com/2015/06/blackstone-mosfet-overdrive.html)

There are lots of demos, this is just the first one:


I think you are going to end with something like a Tech 21 character series. Cascaded gain/clipping stages with heavy filtering/shaping in between but with lots more knobs.
Title: Re: Low Gain, neutral dist/OD
Post by: Fancy Lime on December 30, 2019, 01:50:08 PM
Hi Killthepopular,

from your points 4 and 6, I take it that you want a bit of high cut before clipping. Ponit 5 indicates that you seem to like some higher order harmonics. Let me explain:

The Tube Screamer and Llama have very high input impedance (hundrets of kiloohms), the transistor circuits have very low input impedance (single digit kiloohms). When placed first in your signal chain after the guitar (with no buffers in between), then the inductance of the guitar pickups and the input impedance of the distortion form a low pass filter together. With the high input impedances of opamp or CMOS devices, the cutoff is usually above the audio band but with the low impedances of the transistor circuits, you can hear it This loss of highs can be quite pleasing and is often described as "warmth". Interestingly, when you turn down the volume on your guitar, the extra resistance in line with the inductance of the pickup shifts the cutoff up, so that you get more sparkle when you roll down the volume, which is something many people like. The Fuzz Face is famous for doing that extremely well. You can get the high frequency rolloff before clipping with high impedance inputs as well by simply adding an appropriately designed low pass filter in front of it or increasing the cap in the feedback loop. That does not interact with the guitar volume, though.

The Llama has a rather soft clipping knee, meaning you get a lot of 3rd order harmonics, much less 5th order and hardly anything above that  when you clip it just a bit. This hardly even sounds like distortion at first. If you go to higher gain, you get progressively more of the higher order harmonics. With diodes to ground clippers, you get a lot more of the higher orders early on and if you make it asymmetrical, you also get even order harmonics. I suspect that this is what sounds more exciting to you than the Llama behavior.

If you want it to be able to take really hot input without unpleasant distortion but will have diodes to ground clipping anyway, I suggest to put an additional pair of such diodes to ground before the input coupling cap. This clips any excess signal before it can cause the amplifying element to distort. Whether that should be 0.7V Silicon diodes or red LEDs depends on what stage comes then.

The "3 Sections" plan sounds like a good idea. There is a reason why many people use this exact kind of setup ;) I would suggest to make the first section such that you can either have a full range or a treble boost. If this is only supposed to be an additional clean boost stage in front of the "actual" distortion, then you can probably get away with just a gain pot. You can make it so that gain is minimal with the pot on 12 o'clock and turning it left increases the full range boost, while turning it right from noon increases the treble boost. One knob, two sounds. If that is what you want. This can be done with a few alterations to an Electra-style amplifier stage.

Cheers,
Andy
Title: Re: Low Gain, neutral dist/OD
Post by: Killthepopular on December 31, 2019, 05:51:40 AM
from your points 4 and 6, I take it that you want a bit of high cut before clipping.

The Tube Screamer and Llama have very high input impedance (hundrets of kiloohms), the transistor circuits have very low input impedance (single digit kiloohms). When placed first in your signal chain after the guitar (with no buffers in between), then the inductance of the guitar pickups and the input impedance of the distortion form a low pass filter together. With the high input impedances of opamp or CMOS devices, the cutoff is usually above the audio band but with the low impedances of the transistor circuits, you can hear it. This loss of highs can be quite pleasing and is often described as "warmth". Interestingly, when you turn down the volume on your guitar, the extra resistance in line with the inductance of the pickup shifts the cutoff up, so that you get more sparkle when you roll down the volume, which is something many people like. The Fuzz Face is famous for doing that extremely well. You can get the high frequency rolloff before clipping with high impedance inputs as well by simply adding an appropriately designed low pass filter in front of it or increasing the cap in the feedback loop. That does not interact with the guitar volume, though.

I think you're probably right about point 4. If i don't like a certain twanginess to the llama which I don't hear in the electra then it sounds correct to me that there is a LPF in the pre clipping stage. That makes sense. I'm not sure I agree that this also applies to point 6. There's a certain sweet, musical quality that I'm hearing when I compare transistors and opamps. The difference sounds like more than just a difference in the amount of high frequencies, although it's hard to say exactly what it is. The sound or feel is "sweeter" but not necessarily brighter or darker. Opamps seem to sound a bit flat by comparison. If anything the transistor circuits seem to sound a bit brighter, like the sound is sort of being subtly focussed in a midrange area that sounds really flattering to the guitar, whereas opamps seem to mostly sound like a very flat response which is less pleasing to the ear. It feels as if the transistor is "hearing" my guitar in a more intelligent way, whereas the opamp doesn't understand what it's hearing and processes the signal less sypathetically. Maybe the input impedance is part of what I'm hearing when I talk about "warmth" but I'm not convinced that it's the whole story.

I'm not sure if I like the idea of a pedal that changes the tone with the volume knob. Presumably I could set up the transistor in such a way that it has a high input impedance (e.g. the input buffers of a ts9 or DS1) and then use an RC filter to manually set an LPF rather than sort of "leaving it to chance" and relying on the input impedance to give me my pre-clipping high end rolloff?

Point 5 indicates that you seem to like some higher order harmonics.

The Llama has a rather soft clipping knee, meaning you get a lot of 3rd order harmonics, much less 5th order and hardly anything above that  when you clip it just a bit. This hardly even sounds like distortion at first. If you go to higher gain, you get progressively more of the higher order harmonics. With diodes to ground clippers, you get a lot more of the higher orders early on and if you make it asymmetrical, you also get even order harmonics. I suspect that this is what sounds more exciting to you than the Llama behavior.

This sounds right to me. Diodes to ground has almost always been the most "exciting" sound for me so I guess it's the way to go. The only concern will be to construct the circuit in such a way that I can still get smooth low gain clipping.


If you want it to be able to take really hot input without unpleasant distortion but will have diodes to ground clipping anyway, I suggest to put an additional pair of such diodes to ground before the input coupling cap. This clips any excess signal before it can cause the amplifying element to distort. Whether that should be 0.7V Silicon diodes or red LEDs depends on what stage comes then.


Sounds like an excellent Idea. I know the ROG Ginger uses Red Leds to ground BEFORE each of its transistor boost stages and that circuit sounds really good to me.

You can make it so that gain is minimal with the pot on 12 o'clock and turning it left increases the full range boost, while turning it right from noon increases the treble boost. One knob, two sounds. If that is what you want. This can be done with a few alterations to an Electra-style amplifier stage.


(https://i.postimg.cc/BLhBwSS1/Folk-Driver.gif) (https://postimg.cc/BLhBwSS1)

Like this?

In this thread https://www.diystompboxes.com/smfforum/index.php?topic=122356.msg1153524#msg1153524 I was trying out a few different transistor boost circuits. I was thinking I might figure out what the difference is between some of them and figure out what I like and then stick some diodes clipping to ground in there. Start building my circuit that way. Currently fiddling about with the LPB1 circuit.
Title: Re: Low Gain, neutral dist/OD
Post by: Killthepopular on December 31, 2019, 05:57:02 PM
When I listen to my recorded clips of the circuits I've built I seem to hear something nice and "musical" in the transistor based circuits whereas the opamp circuits sound sort of flat and stiff by comparison. I wanted to test this observation a bit further so I breadboarded the lpb1 and the mxr micro amp and compared them. I found the same thing with these two circuits. The most obvious difference is that the micro amp has way more high end which makes it sound harsh but there's more to it than that. The low end also feels stiffer somehow. It's like the frequency response is too flat whereas the response of the lpb1 subtly emphasises some flattering frequencies. I can't really articulate exactly what the difference is other than to say that (besides the obvious difference of input impedance) the transistor sounds sweeter and more musical somehow.

So if i want to mainly use a transistor boost section but I want my clipping to come from the diodes, not from the transistors (which often sound crackly or farty or gargly to me) then it would appear that I want a transistor based boost with as much output and as much clean headroom as I can manage.

How would I go about making a transistor boost that gives me the most gain possible without distorting too much?
Title: Re: Low Gain, neutral dist/OD
Post by: Fancy Lime on January 01, 2020, 05:40:30 AM
OK, I think I get what you mean by "sweetness" of transistors as opposed to opamps. The thing is, opamps are a lot better at reproducing the original signal in amplified form than simple transistor circuits. Transistor circuits always distort the waveform slightly*, although not enough for us to perceive that as "distortion". Instead, we only notice that it seems "harmonically enhanced" or"sweetened". This is partly because human ears are pretty bad at Fourier analysis of waveforms and partly because we are feeding these circuits with a guitar signal, which has a lot of harmonics to begin with, so a little more harmonics don't make it seem obviously distorted. What many simple transistor designs do really well, is add some rater soft asymmetrical distortion. The Dallas Range Master is famous for that. A good analysis is found here:
https://www.electrosmash.com/dallas-rangemaster
So if this subtle sweetness is important to you, going with discreet transistor designs is probably a good idea.

...

How would I go about making a transistor boost that gives me the most gain possible without distorting too much?
Funny you should ask... This is precisely what I tried to achieve with the 250 Biturbo:
https://www.diystompboxes.com/smfforum/index.php?topic=123610.0
The initial idea for it came from your thread that we are talking on right now, btw so thanks for that! For your specific wants and needs, you may want to modify some things like so:

(https://i.postimg.cc/34Lw5Wzn/250biturbo03.png) (https://postimg.cc/34Lw5Wzn)

This design allows to get very high gain from a discreet design (but gain range starts clean) without ever getting the transistors themselves to clip. The trick is that the clipping diodes limit the bootstrapping, thus limiting the gain of the circuit dynamically. I'm sure someone else has done that sort of thing back in the 70's or so but I am not aware of any other designs using that trick in this way.

R10 needs to be adjusted to get ~4.5V at the collector of Q2. Q1 and Q2 should be low noise, high gain NPN transistors. I used 2N5088. 2N5089 or MPSA18 will work fine and have even better noise specs (otherwise they are essentially the same transistor), BC549C or BC550C should also be fine. Q3 can be 2V4403, 2N2907A, 2N5087, BC560 or any other small signal PNP. It is possible to modify the design to use an NPN in the Q3 position if you don't have any PNP's around. Let me know if that applies and I'll try to find a minute to draw that schematic. I only used a PNP because it allows to draw a neater schematic without crossing wires and the layout for the PCB is easier.

The Boost pot is at minimum at 12 o'clock and lets you dial in a treble boost going counterclockwise or full range boost going clockwise. This is what Imeant in my earlier post (so not really like the Folk Driver but the ideas are related). The Boost switch can be a foot switch. That way you have two different gain levels and gain structures on tap. The maximum gain on this thing is substantial. I used it with back to back 2V7 Zeners (clipping threshold ~3.4V) and it still gets very distorted on max. You can use any clipping diode arrangement of you choice in place of D2 and D3. Considering the gain range, you may want to go for higher thresholds, something like 2xSi in one direction, red LED in the other. With germaniums it may get too gainy so that most of the gain pot travel will not be very usable. Experimentation encouraged, as always.

If you want the thing to sound a bit darker, try increasing C8. You could try 1n and see if you need to go even higher (meaning darker) or take it back down again. R12 and C12 make a fixed low pass filter at ~7kHz as a sort of absolute minimalist tone control. These could be replaced with a proper variable high cut tone control. I'll try to design that in the days to come if I find the time. Been meaning to do that anyway.

Hope that helps,
Andy

P.s.: If you build this thing, I'd be much obliged to read your thoughts and maybe hear some sound samples.

* EDIT: I should probably have written here that "transistor circuits typically have stronger non-linearity than opamps" instead of calling it "distortion". The slight non-linearity in a (theoretically) clean amplification circuit *is* a kind of distortion but it's not the thing that we usually mean when we discuss methods of distortion. So "non-linearity" would have been the less confusing term to use here.
Title: Re: Low Gain, neutral dist/OD
Post by: Killthepopular on January 04, 2020, 06:13:55 AM
OK, I think I get what you mean by "sweetness" of transistors as opposed to opamps. The thing is, opamps are a lot better at reproducing the original signal in amplified form than simple transistor circuits. Transistor circuits always distort the waveform slightly*, although not enough for us to perceive that as "distortion". Instead, we only notice that it seems "harmonically enhanced" or"sweetened".
The slight non-linearity in a (theoretically) clean amplification circuit *is* a kind of distortion but it's not the thing that we usually mean when we discuss methods of distortion. So "non-linearity" would have been the less confusing term to use here.

Yeah this makes sense. I hear a lot of people saying that transistors distort like tubes, when we all know that overdriven transistors tend to sound like old fuzz pedals, not like tubes. Transistors sound tubey to me so long as you don't get them to actually properly distort. I wanted to say that transistors sounded more "compressed" but I thought that didn't make sense, but maybe they are slightly more compressed somehow, as part of their subtle, always slightly distorted sound.

I've ordered some 2n5087s so I might try your circuit at some point. That won't be for a while though. For now I'm going back and trying those transistor boosts again, the ones from my other thread, and adding clipping diodes to them to see what kind of distortion circuits they make. So far I like the LPB1 more than the EP3 or the electra circuits. I like it both as a subtle tone colour boost and also a distortion (with clipping diodes). I'm working on the Zvex SHO now.

Something odd i noticed. I'm sticking some diodes in after the last capacitor (in the boost circuit) and then sticking a volume pot after the diodes. Sometimes it sounds like the signal gets less distorted as it gets quieter and more distorted as it gets louder. It's like the volume pot is affecting the gain before the diodes even though I'm placing it after. I added another 0.1uf cap between the diodes and the volume pot and this seems to have stopped the effect, so now the distortion level stays the same even when i turn down the volume. The 0.1uf cap seemed to cut the bass very slightly. I switched to a 0.22uf cap and didn't hear the bass cut effect any more.
Title: Re: Low Gain, neutral dist/OD
Post by: Killthepopular on January 06, 2020, 06:48:28 AM
(https://i.postimg.cc/w12FfgZr/alembic-stratoblaster.png) (https://postimg.cc/w12FfgZr)

(https://i.postimg.cc/vDnhRWCf/LPB1.gif) (https://postimg.cc/vDnhRWCf)

(https://i.postimg.cc/WhPnsdPK/sho.png) (https://postimg.cc/WhPnsdPK)

I'm having trouble with these circuits. I've been adding diodes after the circuit and then following them with a volume pot. I find that the volume pot seems to lower the gain even though I'm placing it after the diodes, so that the circuit, when I turn down the volume pot, gets quieter and cleaner. With the lpb and the SHO I put a capacitor between the diodes and the pot and I found that this reduced the effect. With the stratoblaster I found that the cap didn't seem to help. I replaced the cap with a 10k resistor and this helped a lot. Then I tried a 100k and this was even better but it seemed to reduce the output level too. I have my amp set very clean and the output level of these circuits doesn't seem that High so I assume the amount of gain in my amp is not the issue and that it is something going on within the circuit itself.

Anyone know what the nature of the problem is here? And what would be the standard solution?
Title: Re: Low Gain, neutral dist/OD
Post by: Killthepopular on March 05, 2020, 05:26:15 PM
(https://i.postimg.cc/8jw5pLtH/DS1-boost.jpg) (https://postimg.cc/8jw5pLtH)

How's this look? This is what I'm currently liking as my neutral, amp-like OD solution. It's a modified version of the transistor boost section of the DS1. I wanted something that went from clean to slightly dirty and what I've found is that circuits tend to sound good at a certain gain level and not so good at others and with this one I'm definitely favouring the clean sound. It's good for a not quite clean tone but as soon as you get it to crunch it starts getting a bit farty. It's one of the worst sounding dirt circuits I've tried but that's ok because the clean sound is (to my ears) nicer than any of the others I've tried. I think the reason I like it is that it seems to be a circuit with a very low input impedance and this gives a really warm, dark mellow tone. If I stick a buffer before it the sound suddenly seems very shrill so it's a pedal I would have to use first in my chain. The gain knob crackles slightly when I turn it but I don't mind that. I tried using circuits with a better input impedance and using a LPF to get the same mellow tone but it never sounded as good as this low impedance circuit. The sound was much more dead and flat. Incidentally I am just guessing that it has a low impedance from the way it behaves. I don't know how to work that stuff out.

I tried out a lot of different circuits and found that opamp based circuits weren't as nice. I then toyed around for a while with circuits with transistors and clipping diodes but i found that the nicest, purest clean sound always came from a circuit with just 1 transistor and no diodes and it could still give me a little dirt for a not quite clean tone.

What do you reckon? Does it look like an ok cleanish boost circuit? I just wanted to double check in case I'd done something that didn't make sense from a technical perspective. I'll probably start figuring out how to do a vero layout next.
Title: Re: Low Gain, neutral dist/OD
Post by: marcelomd on March 05, 2020, 08:21:05 PM
This is almost the same circuit as the Zvex Super Hard On, with a BJT in place of the MOSFET and different biasing.

I think FETs (MOS- and J-) break up in a nicer way. Try it =)
Title: Re: Low Gain, neutral dist/OD
Post by: Killthepopular on March 06, 2020, 04:32:21 AM
I think FETs (MOS- and J-) break up in a nicer way. Try it =)

You mean like a bs170 and j201? I have those. I already tried it with a bc548 and the clipping was way better but it didn't have the same soft impedancy sound to it so I stuck with the 2n3904. I've already breadboarded the SHO and the dirt is great but the tone is much too edgy for my tastes. I much prefer the LPB1 even though the dirt sounds less natural.
I think I'm generally favouring the quality of the cleans over the quality of the grit.
So can I just substitute those transistors for the 2n3904? Is it like
C=D
B=G
E=S?

EDIT: Hang on a minute. If my circuit is essentially the SHO but with a different transistor and biasing, if I switch to a BS170 and adjust the biasing accordingly won't I pretty much just end up with an SHO?
Title: Re: Low Gain, neutral dist/OD
Post by: marcelomd on March 06, 2020, 02:51:20 PM
This is the SHO:
(https://encrypted-tbn0.gstatic.com/images?q=tbn%3AANd9GcScjkrzOkvw8T_7RvgWdPZacSF3F9NihdUjxzzWifzxL1oyB30T)

Actually this is just a textbook common emitter (common source, for FETs) transistor amplifier with self biasing. The only noteworthy part of it is the gain knob which is not bypassed with a capacitor, and maybe the really big input impedance.

If you try a MOSFET, don't forget to use protection diodes (or a zener between source and gate).
Title: Re: Low Gain, neutral dist/OD
Post by: Killthepopular on March 07, 2020, 06:16:06 AM
This is the SHO:
(https://encrypted-tbn0.gstatic.com/images?q=tbn%3AANd9GcScjkrzOkvw8T_7RvgWdPZacSF3F9NihdUjxzzWifzxL1oyB30T)

Actually this is just a textbook common emitter (common source, for FETs) transistor amplifier with self biasing. The only noteworthy part of it is the gain knob which is not bypassed with a capacitor, and maybe the really big input impedance.

If you try a MOSFET, don't forget to use protection diodes (or a zener between source and gate).

I'm pretty certain that I like low input impedances (for the first pedal in the chain obviously) and that the SHO is one of my least favourite boost circuits because it is so bright, although it distorts nicely. How would I go about lowering the input impedance of the SHO? Could I swap r1 and r2 for 100k? Or could I just keep the circuit as is and add a 100k pulldown resistor before the input cap?
Title: Re: Low Gain, neutral dist/OD
Post by: Fancy Lime on March 07, 2020, 06:36:21 AM
It may be worth noting here, that the input impedance of stages like the SHO is not determined by R1 and R2 alone but also by source resistor and the properties of the (individual) MOSFET. Since the gain control ("crackle") changes the source resistance, the input impedance changes from a few MΩ at minimum gain to much lower values at higher gain. All things considered, this is not really a high input impedance stage.

Also: lowering the input impedance only makes sense (to me) if you match it to the output impedance of the guitar you are going to be using it with. Playing a Les Paul and a Tele into the same low-impedance stage will give very different results. And I mean different beyond the differences of the guitars. If you only use one guitar or several very similar ones, no problem. If you are using a Les Paul and a Strat, I would suggest making separate pedals for each or one pedal with several different impedance inputs, like many old tube amps had. Or you could just go with a very high input impedance booster/overdrive, which does not interact with the output impedance of the guitar (much) and tame the highs with a variable low-pass filter. The latter option is by far the most flexible and easiest to implement.

Cheers,
Andy
Title: Re: Low Gain, neutral dist/OD
Post by: Killthepopular on March 07, 2020, 09:26:25 AM
You could just go with a very high input impedance booster/overdrive, which does not interact with the output impedance of the guitar (much) and tame the highs with a variable low-pass filter. The latter option is by far the most flexible and easiest to implement.

I have toyed with this idea briefly. What I found was that a higher impedance circuit with a LPF sounded dark in a very different way from how a low impedance circuit sounded. The high impedance circuit would sound harsh without the LPF or would sound mellow but excessively muffled with the LPF. The low impedance circuit sounded mellow in a way that seemed more natural and better balanced. If I had to guess the difference it would be that the low impedance sounds like it rolls off the high frequencies in a much more gradual way than the typical 1st order RC filter. I don't know if the physics/math backs up this theory but that's what it sounded like to me.

Either way it seems to me that a low input impedance does something special to the sound which I like a lot, which doesn't sound the same as just incorporating a LPF into the design. I probably need to do more experiments on this to feel 100% confident about it. Perhaps I can make an SHO and add a LPF (before the transistor I suppose) and compare that to how it sounds if I add a low value pulldown resistor to lower the input impedance (assuming that this will work, haven't tried it yet).
Title: Re: Low Gain, neutral dist/OD
Post by: marcelomd on March 07, 2020, 10:21:37 AM
Hi,
You could try a low impedance BJT stage into a SHO (or anything else, like the llama variants that were discussed).
One gain knob for each stage. Or a dual gang, or a trimmer and one pot, etc.
Title: Re: Low Gain, neutral dist/OD
Post by: Killthepopular on March 07, 2020, 10:45:22 AM
You could try a low impedance BJT stage into a SHO.

I don't want to sound like The Princess and the Pea but I find that 2 transistors don't seem to sound as good as one. Opamps have a less musical, more stiff, surgical sound. Single transistors seem to have a more musical sound somehow, more valvelike, even when completely clean. 2 transistors seems to pull the sound towards that stiff, flat, opamp sound and away from the sweeter sound of 1 transistor. Again, this is something that I've noticed and is specific to my own subjective experience of my listening tests. I'm heavily inclined to make whatever circuit I finally build just be 1 transistor and not much else. I know it limits my options but If I want the best possible vanilla, always on tone I can get then I don't believe I can do better than a 1 transistor circuit.
Title: Re: Low Gain, neutral dist/OD
Post by: Fancy Lime on March 07, 2020, 12:09:42 PM
You could just go with a very high input impedance booster/overdrive, which does not interact with the output impedance of the guitar (much) and tame the highs with a variable low-pass filter. The latter option is by far the most flexible and easiest to implement.

I have toyed with this idea briefly. What I found was that a higher impedance circuit with a LPF sounded dark in a very different way from how a low impedance circuit sounded. The high impedance circuit would sound harsh without the LPF or would sound mellow but excessively muffled with the LPF. The low impedance circuit sounded mellow in a way that seemed more natural and better balanced. If I had to guess the difference it would be that the low impedance sounds like it rolls off the high frequencies in a much more gradual way than the typical 1st order RC filter. I don't know if the physics/math backs up this theory but that's what it sounded like to me.

Either way it seems to me that a low input impedance does something special to the sound which I like a lot, which doesn't sound the same as just incorporating a LPF into the design. I probably need to do more experiments on this to feel 100% confident about it. Perhaps I can make an SHO and add a LPF (before the transistor I suppose) and compare that to how it sounds if I add a low value pulldown resistor to lower the input impedance (assuming that this will work, haven't tried it yet).

True, the interplay between guitar pickups and input impedance of the first pedal is a bit more complicated than a simple low pass filter. Essentially, they make up a LRCR lowpass like this: The DC resistance (R) and inductance (L) of the pickup are in series with each other and with the signal. The capacity of the guitar cable, the capacity of the MOSFET (or whatever) input, the resistance of the guitars volume pot and the resistance provided by the input impedance are all in parallel to ground. This is a two-pole aka second order filter. What kind of response you are getting from that is difficult to predict because it depends hugely on the inductance of the pickups (and therefore also on the position of your pickup switch) and the impedance of your guitar cable (which can vary from under 100pF to several nF). So any simulation of this is going to be no more than an approximation. One thing that is certain though, is that it is not "more gradual" but "less gradual" than a simple low pass. What makes it sound "more natural" is, at least in my experience, probably a slight resonant peak just before the roll-off edge. I have recently modded a bass to make use of this passive treble boost effect and I really like it.
A really easy  way to make use of the "low impedance effect" while also retaining the flexibility that allows you to tune it to different guitars, is to add a 1MΩ pot, wired as a variable resistor to ground before C1 (in the SHO schematic). With that you can then tune the input impedance to whatever sounds best (as long as it is under 1MΩ || SHO input impedance).

Andy
Title: Re: Low Gain, neutral dist/OD
Post by: marcelomd on March 07, 2020, 03:34:26 PM
Quote
I don't want to sound like The Princess and the Pea but I find that 2 transistors don't seem to sound as good as one.

Nah, it's all good fun working within constraints, but at one point it's a "short blanket" issue, as we say here. You cover either your feet or your shoulders, not both.

Let's see... a Darlington or Sziklai pair counts as one or two? =)
Title: Re: Low Gain, neutral dist/OD
Post by: AndersonENGINEERING on March 14, 2020, 08:47:47 PM
What about a lovepedal eternity clone? I just wrapped on up with germanium diodes and I must say that it turned our great. Not a ton of gain or volume as a whole, but it's a great all around pedal.
Title: Re: Low Gain, neutral dist/OD
Post by: Killthepopular on April 29, 2020, 05:42:01 PM
What about a lovepedal eternity clone? I just wrapped on up with germanium diodes and I must say that it turned our great. Not a ton of gain or volume as a whole, but it's a great all around pedal.

Isn't that just a variation on the son of screamer? I've breadboarded that already. It's very good but I don't like the feel for some reason. Too compressed maybe.
Title: Re: Low Gain, neutral dist/OD
Post by: Killthepopular on April 29, 2020, 05:53:56 PM
https://mega.nz/file/hqQjHYpL#n8I7EiD0HMwDXTbDH9E8z1JvSZ6sES6jx3AmiXYZnNs

This is some bluesy noodling I was just doing with my breadboarded DOD 250. Hopefully that link works.

When I first tried out the DOD I was like "YOU KNOW THAT NEW SOUND YOU'VE BEEN LOOKING FOR? WELL LISTEN TO THIS!" but then I found when listening to recordings I'd made of it that it was very thin and the distortion wasn't very natural. I've breadboarded it a second time and discovered that the gain knob is really more of a tone control and the volume control is more of a gain control, and with that in mind I'm getting much better tones out of it and finding that it's one of the most responsive and dynamic sounds I've ever found from my gear.

The clip is my gretsch > Dod 250 circuit > ROG Condor > marshall reflector > soundcard. It was sounding good to me... I'm leaning towards making the DOD. I'm really looking for my always on tone, y'know how so many guitarists say "this is my clean tone" and then kick on an overdrive? That's what I'm looking for and I feel like the DOD might be right for that.

I still wanna have a look at a few more circuits like the nobels and the big muff and might also take a second look at the rat and the hotcake. The hotcake that I breadboarded was this weird mix of a super distorted signal and a clean signal and the gain control just raised or lowered the volume of that distorted signal. It sounded weird. I'm wondering if I made it wrong and it isn't really supposed to sound like that so I might take a second look.
Title: Re: Low Gain, neutral dist/OD
Post by: aron on April 29, 2020, 10:33:39 PM
I've been using the Shaka HV with Shaka Braddah III type clipping diodes for years. I can play all night with it on for most bluesy gigs unless I really need to be absolutely clean, then I turn it off.
Title: Re: Low Gain, neutral dist/OD
Post by: niektb on April 30, 2020, 03:53:29 AM
Have you tried the Fetzer Valve? :)
You can easily give it a high and low impedance input to match the guitar you're playing, it has very few components and should sound a bit tubish :) (or at least it tries to emulate a vintage Fender 12AX7 input stage hahah)
http://www.runoffgroove.com/fetzervalve.html

it only needs a bit of work to bias it properly, or you could self-bias it with another JFET like what happens in the AMZ minibooster :)