The most common problems that causes swelling / fading in fuzz?

[Woolly Mother Mammoth]

Hi There!!


Ok, I've built a octave fuzz (tone machine/ultimate octave-style) but it is heavily and heavenly modded.   It works as a charm and I only got one tiny problem; when I play attacky hi notes the volume tends to back down and fades in slowly as the attack gone down. I get the same but more of it while using a wah in front of the fuzz (yepp, I like it there!). That would be my main problem.

So what are the most common problems when a fuzz begins to swell/fades in on attack? I noticed that the greater sustain I dial, the more it swells.

Hugs and a lot of love!
Ben

[Woolly Mother Mammoth]

Did I get too complicated? Did I write too much? Anyone....help? 

[artifus]

schematic? sounds like cap recovering in a comp/limiter scenario.

[slacker]

Some octave pedals just do this, especially at high gains the two halves of the rectified signal basically cancel each other out so you get a quiet signal or even no sound on attacks, then as signal decays the sound swells back in. Too much gain somewhere can also cause the same thing, for example if you stick a booster in front of a Big Muff you'll get the same sort of swell you're getting.

[boogietone]

Interesting. I have to go experiment with this.

[LucifersTrip]

I've gotten swelling/mild gating many times when the transistors are not biased properly...

[R.G.]

Unless this is being done intentionally in some way, it's always a bias-shift causing it.

In fact, most of the time it is being done intentionally, it's done with bias shift. You just know it ahead of time in that case.

[Woolly Mother Mammoth]

Wow, thanks for the response! I will definitely take a look at the biasing on the last stage of the pedal, I added one to get a bit of extra volume.

[Woolly Mother Mammoth]

Thank you all for responding! I almost solved the problem by adjusting the bias on the sixth transistor stage, a simple buffer stage. I swapped the previous 560Ω for a 1k and now swelling effect is almost gone when the octave is not engaged. I think I'll tinker a bit more with it and see what else can be improved.

I also noticed that when dialing the tone control (a custom big muff tonestack with huge bump at 100hz) all the way to "bass" the swell became even more extreme.

Thanks again, you all save me some major debugging time!