Tone Bender Mark II Hiss

[DaveTV]

So far I've tried two attempts at building the Tone Bender Mark II using a transistor set from Small Bear and both circuits generated an enormous amount of hiss when the gain knob is turned up. Otherwise, I'm really digging how this pedal sounds--amazing fuzz!--and would like to get it working properly. The schematic I'm using is the PNP negative ground version. The information Steve sent with the transistors showed resistor values identical to those in the original circuit.

For the first build, I tried squeezing the circuit into a B-sized box. With this build, I got some nice oscillation and hiss. I was able to eliminate the oscillation with shielded cable, but was left with the hiss. I thought spreading the components out might help eliminate the noise, so the second build was on a larger board into a BB-sized box. No oscillation this time, but still plenty of hiss.

I measured the voltages on all 3 transistors in both builds and they were the same both times. All values appear to be in the range of what other people have posted. The only difference is the base voltage on Q1 is a bit higher on mine. I'm measuring over 500mV as opposed to less than 100mV that I've seen described elsewhere. Other than that, I'm having trouble figuring out what the source of the hiss may be. I may try ordering another set of transistors to see if that solves the problem, but was wondering if anyone else had any troubleshooting suggestions first.

[foxfire]

if you haven't already, do a search for negative ground tone bender. i'm pretty sure that i remember hearing that there are sometimes issues with doing negative ground pnp circuits like this.

[col]

Use an audio probe to see where the hiss is originating, either in the darlington pair or in the final transistor. It may be that one of your transistors is producing it, a lot of Ge ones do. Try socketing a few and see if that helps.

[DaveTV]

Thanks guys. I think I may go back to the breadboard with this one and see if I can play around with the transistors a bit. I also do have a set of matched transistors for a Fuzzface. Perhaps I can make use of them for this problem.

[MartyMart]

PNP with neg ground can be a real PITA !!
I would recommend to rewire with positive ground, I bet it sounds great right away

[petemoore]

The schematic I'm using is the PNP negative ground version.
 If you're into tonebenders,  convert or build one to a ground scheme other than PNPNG, that's the only way I can figure for you to know what difference there is in TB ground schemes. The FF and TB PNPNG circuits have problems often enough, many are ditched as 'intractably problematic'.
 Maybe try some NPN ge's.
 That said, I remember getting hiss after reverse polarizing caps or Ge's, could be a misnomer.