Parentheses Fuzz: Weird octave knob oscillation issue

jeffwhitfield

Well-known member
Ok, so, here's a weird one for you. Out of the 10 Parentheses Fuzz pedals I built, one of them has a problem that still eludes me. Basically, when the distortion is on and octave is off, if I turn the Octave knob up all the way and start playing I get a weird solid tone hum...almost like it's oscillating or something. Turn the Octave on and the problem goes away. It's only when the Distortion is on, Octave off, with the Octave knob turned up all the way. If I start to back down the Octave knob, the problem gradually disappears. Weird, right?

I tried switching out the diodes for the octave stage but that didn't do anything. Did a full reflow of all the solder points. Now I'm starting to think that there's a bad component on the board. Looking at the schematic, could it be one of the capacitors in the path around the octave stage? Maybe C6 or C7? Those are the only ones close to the Octave pot so, with the switch turned off, could it be that one of the capacitors is allowing the Octave stage to bleed through?

IMG_0591.jpeg
IMG_0592.jpeg
 

jeffwhitfield

Well-known member
Alright, so I did a signal trace on the board. With the Octave all the way up, the tracer does indeed register the feedback. After running the trace, I narrowed it down to Q1 which is a PF5102 transistor. Leg coming in was fine but the leg going out shows the feedback. The R4 resistor is reading the correct resistance (10k) so it seems to Be a bad transistor. Ordered some new ones so I guess we’ll find out. 🤞😁
 
Top