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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