Roger Mayer Axis Fuzz Capacitor Values?

[To The Moon]

Hey all, I have an axis fuzz with some bad noise filtering issues, not a ground issue, sounds like amp filter caps. If I go about replacing the 22uf caps to try and remedy it should I stick with the 22uf value? All I've got at home right now are 10uf, 37uf, and 100uf. I know in plenty of fuzz circuits these big caps hardly make any difference between 1uf and 100uf but I don't want to stick anything in that will have a negative effect.

[Rob Strand]

I'm assuming you are having hum and buzz issues when using an external power supply? 

The schematic I have does not show any filtering on the supply rail.  The existing caps only affect the first stage.  Changing the value will have minimal effect and has no effect on the second stage.  Perhaps a better solution is to put a 100uF across the whole supply rail.  Better still would be to add a 100 ohms in series with the in-coming rail then a 100uF across the power rail on the circuit side.   Adding the 100ohm + 100uF filter is a good generic solution for fixing PSU noise issues on those older transistor based effects pedals.

[To The Moon]

I don't use a power supply with it, only battery. Weird!!

[Rob Strand]

I don't use a power supply with it, only battery. Weird!!

It wouldn't hurt trying a 100uF cap across the power rails.
At least then you know junk is getting on the power wiring then getting to the output.

Beyond that you could have some sort of fault: faulty socket, switch fault, broken wire.

After that maybe investigate oscillation issues.  As a test:, try a 100pF to 1nF cap across the input.  This *does* affect the tone but the point it  lets you know what type of problem you are dealing with.  Once you know that you can try to solve it in a way which has the least impact.

[To The Moon]

Thanks! I'll try both tonight and be back when that's done.

[To The Moon]

I don't use a power supply with it, only battery. Weird!!

After that maybe investigate oscillation issues.  As a test:, try a 100pF to 1nF cap across the input.  This *does* affect the tone but the point it  lets you know what type of problem you are dealing with.  Once you know that you can try to solve it in a way which has the least impact.

ok just plugged it in again, it occasionally oscillates! Playing doesn't make it go away, either. Just happens in the background. Got to do dig around for capacitors.

[j_flanders]

All I've got at home right now are 10uf, 37uf, and 100uf.

Two 10µF's in parallel are 20µF
Two 37µF's in series are 18,5µF
That 37µF and 100µF in series is 27µF
All of that is close enough to 22uF.

[Rob Strand]

Is this a DIY unit or a commercial unit? 
Also, did it work once and not now, or is this a new build?

If it is a DIY unit you might want to post the schematic you used.  IIRC there was a bug on one of the Axis fuzz schematics.

ok just plugged it in again, it occasionally oscillates! Playing doesn't make it go away, either. Just happens in the background. Got to do dig around for capacitors.

OK at least you know.

I just took another look at the schematic and that circuit already has a 470pF cap on the input (assuming you have that on your build).

I suspect it might be possible for that unit to oscillate if one of the 22uFs is stuffed.