Univox Square Wave

[snk]

Ok, I just finished to build it, and once again I have to thank you Mark for your great tips and mods suggestions :
- The GAIN knob is very handy to have to dial distortion to taste;
- I think that the stock sound is a bit too compressed to my taste, but with the diode lift switch, it sounds like a nice, warm and loud overdrive

If I wanted a little less distortion and a less bright tone/dist knob, how should I tweak it? I'd like to have a lower range of tone (from bass-heavy to "not-as-trebly-as-it-is-now"), because i don't think i'd go over 3 o clock as it is now...
- trying a lower value for the "distortion" pot (like 50k)?
- which component sets the fixed gain (so i can try to reduce the overal fixed gain)?

[Mark Hammer]

When there is a lower-resistance path to ground for AC from the FET source pin, the gain gets higher.  The suggested pot in series with the 33uf electrolytic cap allows for varying the gain by varying that resistance.  If you find that last bit of increased gain a little much for your tastes, just stick a small-value fixed resistor in series with the Gain pot, like 100-220R.

Note as well that the value of that 33uf cap determines how far down in the spectrum that gain-increase is applied.  Reducing the value of that cap will apply less gain to the bass region.  You might find that 10uf or even 4u7 gives you a more "even" distortion across the spectrum, by applying a bit less gain to those regions where the signal amplitude is already higher.

If you prefer to run the unit without the clipping diodes, I think you'll find there is more than enough signal level to make use of a passive tonestack feasible.  That could be something like a one-knob Big Muff tone control.  Normally, such passive tone controls eat up (bleed off) enough signal that you're not left with much unless you add a gain recovery stage like the Big Muff does.  But here, the "unclipped" Squarewave circuit has more than enough signal to spare.

A traditional Big Muff tonestack is geared more towards getting a midscoop, with "woolly" sounds at one end and "mosquito buzz" at the other.    Consider using 39k/4700pf on the bass side and 39k/8200pf on the treble side for a more even and "throaty" range of tones that won't get as woolly or buzzy at the extremes.

[snk]

Thank you, Mark.

I'll try that  small-value fixed resistor in series with the Gain pot tip.

Interesting. Just to be sure, do you mean that "reducing the value of that cap will apply less gain to the bass region" making the output "less bassy", or making the distortion less sensitive to bass? If I understand you well, I should get as much bass, but less distorted in the low range, am I right?
I'm looking for a bit more bass overall (I already increased the input cap to 150nF, and may try 220nF), and so far it's good, but I could try the extra mile
Making the distortion less sensitive to the bass input could make the sound equally bassy but less aggressive, which might be good.

Mmmh... I feel that adding a BigMuff tonestack would be going too far away from the original design (that Hipass filter called "distortion) is rather unique!), so, I'd rather try to stick to the original design, but trying to tweak it a bit to fit my needs better.
My goal would be instead to just limit the range of the tone ("distortion") pot so it wouldn't go so high. Maybe also taming a bit the highs with a simple cap, but i'm not even sure

[Mark Hammer]

Thank you, Mark.

I'll try that  small-value fixed resistor in series with the Gain pot tip.

Interesting. Just to be sure, do you mean that "reducing the value of that cap will apply less gain to the bass region" making the output "less bassy", or making the distortion less sensitive to bass? If I understand you well, I should get as much bass, but less distorted in the low range, am I right?
I'm looking for a bit more bass overall (I already increased the input cap to 150nF, and may try 220nF), and so far it's good, but I could try the extra mile
Making the distortion less sensitive to the bass input could make the sound equally bassy but less aggressive, which might be good.

That's pretty much what the smaller value electro cap will do.  It's the Tube Screamer strategy.

Mmmh... I feel that adding a BigMuff tonestack would be going too far away from the original design (that Hipass filter called "distortion) is rather unique!), so, I'd rather try to stick to the original design, but trying to tweak it a bit to fit my needs better.

I think by making the gain variable and omitting the diodes, you, me, and Toto aren't in Kansas anymore.  So a Big Muff tone control isn't crossing a magic line AFAIC.  But I respect your feelings on the matter.

My goal would be instead to just limit the range of the tone ("distortion") pot so it wouldn't go so high. Maybe also taming a bit the highs with a simple cap, but i'm not even sure

Just to refresh everyone's memory, here's the circuit of the original.  You can see that it used a 33uf cap to ground but omitted any way to reduce the gain from that maximum.  The diodes kept the overall volume in check and added yet more "squareness".  The stock tone control (labelled "Distortion") basically adjusted how much bass to let through.  IN my own redraw, I added a few caps to ground to help filter out the fizzies.  The 5k6/4n7 pair roll off above 6khz.  For less fizz, make the cap 6n8.

[rutabaga bob]

Here's what I came up with.  Haven't built it yet, but will in the near future.

[Mark Hammer]

I salute your effort, sir.  Good on ya!  And thanks.

[RickL]

I like to complicate things  .

If I was to build this I would replace S1 with a spdt on-off-on switch (won't take up any more room on the panel) and run the extra pole back to the diodes through a resistor. You could either experiment to find out what you like or use a trim pot. Or run the extra pole through a couple more back to back diodes for a higher clipping threshold. Or just one for some some asymmetry (although you might not hear any difference - maybe use an LED). Or through a capacitor (shouldn't that cause only the higher frequencies to get the extra clipping?).

[Steben]

Here's what I came up with.  Haven't built it yet, but will in the near future.

nice

the only thing this thread might need still is soundclips

[rutabaga bob]

Well...I can't help you there - but I agree!