I built a negative ground pnp fuzz face. When I run it off of batteries, it makes an annoying hum when the fuzz is turned all the way up or the guitar's volume is turned all the way up. If I turn either control back, the hum disappears. BUT when I run it off of an AC adapter , there is no hum at all.
I've made the Roger Mayers Hendrix Mods, i.e. 470 to 1K, 8.2K to a 20K trimpot to adjust Q2 collector voltage to 4.5 Volts, 1K fuzz pot to 2K pot. I've also swapped the 2.2uf cap for a 4.7uf cap and added a 1M resistor to ground at the input.
Any help would be greatly appreciated.
THANKS
yeah man, the FF is really susceptible to weird noises. you get some that oscillate if you have single coils but not with humbuckers, some that hum with your guitar volume up full and some that hum with the guitar volume on 0, some that only oscillate with the FF volume on 10 and some that oscillate all the time but the pitch changes when you move the controls around.
you can do a few things to try fixing it:
1. add a large power supply bypass cap, 100uF is good, across the battery. just hook it up right across the + and - power rails. this should lower the impedance of the battery and reduce or kill the weird oscillations
2. add a capacitor across the C and B of Q2. 47pF is a good start, try 100pF or even 220pF if you still get hissy noises and/or radio stations.
3. add a series resistance between the input cap and the base of Q1. this should kill any remaining hum, but reduces the amount that your pedal reacts to volume control changes at the guitar and also reduces max gain after you get above 1k. try 100 ohms, then 1k, then 10k, then 100k.
4. try removing the 1M to ground on the input... you never know. :P
good luck!