Low Gain, neutral dist/OD

[Killthepopular]

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.

[marcelomd]

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 =)

[Killthepopular]

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?

[marcelomd]

This is the SHO:


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).

[Killthepopular]

This is the SHO:


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?

[Fancy Lime]

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

[Killthepopular]

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).

[marcelomd]

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.

[Killthepopular]

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.

[Fancy Lime]

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

[marcelomd]

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? =)

[AndersonENGINEERING]

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.

[Killthepopular]

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.

[Killthepopular]

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.

[aron]

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.

[niektb]

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