So I have a really crap old little 10 watt practice amp,


Its pretty rubbish, but the distortion sound is kinda likeable in a dirty fuzzy way, think big muff but dirtier and harsher.

So i was wondering how easy it would be to take the circuit and make it into a dirty fuzz pedal?

Im thinking the biggest issue is the big chunky mains step down transformer!

but yeah any thoughts/suggestions?
If you're running it into another amp once it's a pedal then you don't want to be taking the output section because the thing would be so fuzzy and crappy sounding. I'd suggest taking just the preamp section with the tone-stack, that's where most of the distortion and tone comes from anyway. The problem with this is, like you said, the massive transformer. I'm guessing it's a transistor amp so you don't neet to worry about tubes, so if the transformer has only one winding and one output votltage you could probably power it through a DC input instead.
Last edited by matt154 at Apr 17, 2011,
Yep, theres what I believe to be a transistor in the centre of the circuit bolted to a heat sink.

The transformer outputs 2 voltages, 21V and 10.5 volts, I was hoping to just whack in a standard Boss type DC jack, to simplify things, is this going to be possible?
Probably not then. The transformer output is AC which is then rectified to DC on the board. If you have a DC input it's hard to up that to the two voltages required, you'd have to do something like make up a DC voltage converter suited to the job. So you'll probably have to keep the transformer (or find a smaller one somewhere that'll do the same job) and then input mains into the pedal. If you want to use a smaller transformer I'd suggest measuring the voltage after a voltage regulator. The voltage regulator drops the input voltage to a set level and this is as low as you can go.
you can power it with DC. the PT is probably a 20v-ish center-tapped, so it supplies about 10v AC to the circuit. after rectification and filtering that turns out to be about 15v. It is probably a bipolar supply (+/- 15v), as I haven't seen an amp that didnt have a bipolar supply.

so a couple of options are to either lower the bipolar supply (if you have an 18v wall wart then +/- 9v would be easiest) or use the transformer and power supply section of the amp as a wall wart. I'd recommend the latter, as lowering the supply will most likely result in a crap sound and no headroom (even though you only want the OD section this will still make a big difference).

as for the actual effect, you'll need to trace out the board (or find a schematic) to identify the OD channel. Then you can rebuild it onto a piece of perf (this is exactly what I am doing with my fender frontman 25R's OD channel, only I am cloning it and not hacking up my only amp).

of course the other option is to just hack 'n' slash it into another box, but then you'd end up with alot of wasted space and extra circuit crap you don't want... either way it'll involve some circuit tracing on your part, as the power amp is integrated with the rest of the board.
ok so im beginning to try to draw up a schematic! Haven't done this in years so feeling a little bit rusty!

Basically from what I can see, the 10.5V tapped from the middle of the transformer goes into a pair of 1000uf capacitors with opposite polarities, each then going into a pair of diodes again with reversed polarity.

One of each of these pairs then connects to the ov and 21v outs from the transformer.

Is this some kinda circuit splitting the positive and negative current?