Foxx Clean And Dirty Sustain.

[kaycee]

I recently got an enquiry about repairing the circuit board from a Foxx - Clean And Dirty Sustain. I looked up the schematic and made a vero to try it out. The results were rather disappointing though. The circuit is a booster, repeated 3 times with output taken from each stage through a rotary switch.

Stage one is a clean boost, stage two gets a bit fuzzy and stage three is quite fuzzy - has good sustain, but isn't very exciting.

In an attempt to liven it up, I added a 22uf bypass capacitor to the emitter of Q1 which gave it a bit more gain, but still didn't make it into a good sounding fuzz.

In my build I used 2M2 instead of 2M7, and used BC108 with hfe @450.

Voltages with a 9 volt supply across the stages are:
C 4.4
B 0.9
E 0.4

Any suggestions for livening it up any further?

[Mark Hammer]

That's a new one on me.  I wonder if Zachary Vex took the inspiration for the Box of Rock from that, given that the BoR is simply three Super Hard On booster stages in a row.

But as for suggestions for "livening it up, why don't you borrow a trick from the BIg MUff Pi and stick a back-to-back pair of red LEDs between base and collector in that 3rd transistor stage.

[antonis]

Try to make 2M7 feedback resistors 470k or so..

[Quackzed]

if you wanted to go in a big muff direction, you could add x----2 clipping diodes-----.1uf cap----x  in parallel with the 220p cap of stage 2 and 3 ( to keep the clean first stage ) or if you want some nasty gated fuzz for the 3rd stage you could put 2 clipping diodes in line after the stage 3 .22uf input cap (germanium or other lower threshold diodes will be less gated)

[iainpunk]

if you want some nasty gated fuzz for the 3rd stage you could put 2 clipping diodes in line after the stage 3 .22uf input cap (germanium or other lower threshold diodes will be less gated)

this type of gate is rough, bit its not nasty like most gated fuzzes. its good for doom metal rather than stoner rock stuff, since it gives more of a grind edge, instead of the broken square waves you get out of a ''wrong bias'' gate (which i would associate more with stoner rock than doom metal)
i echo this recommendation.

you could also throw in a variable (positive) feedback path to make it oscillate do weird stuff.

maybe a mid scoop circuit, or filtering clipping, which changes the tone and is quite unique:


just look at as much fuzz schematics and steal their little tricks.

cheers, Iain

[kaycee]

Thanks very much for the tips, I'll try a few out and report back.

Seems like this came in the fancy foot treadle enclosure that Foxx did, I'm surprised that they put such an underwhelming circuit in one considering how good their other effect pedals were.

Ideally, I'd like to be able to switch between the 'standard' circuit and a modified one - I can change the feedback resistors, then add a switch to throw in the clipping diodes and bypass cap, see if that makes something worth boxing.

[kaycee]

OK, that's better.

Replaced the 2M7's with 470K's and a pair of 3mm red LED back to back over the C/B of Q3. Took the emitter bypass cap on Q1 down to 10uf.

Smoother gain, long even sustain, gets hairier with the cap switched in. Its quite a compressed fuzz, kind of sterile sounding though to my ears.

I'll draw up a vero with the bypass cap and LED on switches - off the top of my head with the rotary gives 8 options.

Thanks for the brainstorm 

[kaycee]

Here is my vero for this.



The 2M7 Collector/Base resistors changed to 470k, other than that with switches 1 & 2 open its the stock circuit.

S1 adds an emitter bypass capacitor to Q1.

S2 adds clipping diodes (2x 3mm red LED back to back) over the collector/base of Q3.

Output is from the right of the board, 1, 2 & 3 go to the throws of the rotary switch. The pole is connected back to the board, through the 220n output capacitor and out to the 1MA volume pot, lug 3 (lug 2 is out, lug 1 to ground)

[duck_arse]

if you switch-add the Q3/third transistor diodes C to B without a blocking cap, it will Bazz more than Muff the last stage, I think.