Need help with Mark Hammer's chaos.

[alparent]

Just finished up my Chaos using Paul Marrosy's layout.
The gain pot doesn't do much? Barely noticeable change between the two extremes. Any tips?

[Mark Hammer]

Do you mean change in level or change in distortion intensity?

[alparent]

change in level.

[Mark Hammer]

Well, you can probably lose the 1M gain pot and just go for a 100k-250k.  That won't change maximum gain.  It will just bring you to maximum gain faster.

Feel free to change the 4k7 ground-leg resistor in stage 2 for 3k3 to add a little more sizzle. THAT will increase overall gain, by bumping up the stage 2 gain from 22x to 31x.  That doesn't sound like much, but remember that it is multiplied by the gain in stage 1.  So if stage 1 is set for a gain of 10, then that's an overall gain of 310x, which is more than a Tube Screamer or Distortion+.  Since the maximum gain of stage 1 = 101x, I think you'll find that 31 * 101 is a LOT of gain.

For tonal reasons, you can consider leaving the gain of stage 2 where it is, and increasing maximum gain in stage 1 by dropping the value of the 10k resistor to 3k9, so that max gain in stage 1 = 257x.  Again, 257 * 22 is a LOT of gain.  The difference is that stage 2 will be hit with a signal that is already more clipped.  If you want a compromise, go with 6k8 instead of 10k, for a max stage 1 gain of 148x.

Remember that the diodes in stage 1 will clip when set to at higher gains, but not that much.  For that sort of diode complement, you generally won't hear obvious clipping until you achieve gains of 60x or more.  The clipping will set limits on maximum amplitude of the signal being fed to stage 2, but more importantly, the signal level is raised again by stage 2 to produce a signal that easily produces heavy clipping.

DO NOT use a diode arrangement in stage 2 that clips at less than 1V or so.  The tone control eats up a lot of signal, so unless you have a very hot output from the op-amp, there won't be much level left after the tone control.  Use of a 2+2 combination gets you that higher threshold.  I suppose you could also use a red LED and pair of Si diodes, or even a pair of red LEDs, for even hotter outputs.

[alparent]

OK compared my chaos with the one you brought me yesterday.
I now have gain! ONE strand of the input wire was sticking out and shorting.

Now I find that the gain pot works pretty much like mine. Give you high gain when at 0 ohm (actually 3 ohm) and gives you (what I'll call low gain) when I get to about 270k. But there is no real progression. I mean from 0 ohm to 270k = high (no noticeable variance) and from 270k to 1M = Low gain.

So I decided to drop the gain pot and use a SP2T switch instead. One trow will just short to give me the 10k fixed resistance (high gain) and the other trow add a 330k (giving me low gain).

I've also noticed that you added a 3.3k resistor and a .047uF cap parallel to the 4.7k and 1uF in stage 2? Please educate me.

[Mark Hammer]

Ah, I had forgotten I did that after I built it.  Just borrowed a trick from the Rat, which also uses two parallel ground legs in the same manner.  The added 3k3/47n network applies a little more gain to the top end than it does to the rest of the spectrum.  At max gain in stage 1, the extra boost starts around 1khz.  Because the network is in series with the gain pot, the added "top boost" is relaxed as the gain is reduced and more resistance is added in series with those two RC networks.

You'll notice it if you max the gain, and turn the tone control to max treble.  At that point, there is enough gain applied to the high end to produce some undesirable "fizz".  You can get rid of that by either rolling back the highs with the tone knob, or by nudging the gain back just a little.