100uf power filtering

[Saturated]

Hi all,
I tried looking to the archives for this, a lot of info there but not specifically what I want. I've been messing around with fuzz face circuits and found one that has a 22uf off the power rail to ground presumably for noise reduction.
I tried applying this to another circuit and found that it reduced the output volume by about 70%. I reduced it to 4.7uf and it works great but does such a reduction negate any noise reduction benefit? I know the standard for this is a 100uf off the power rail. 4.7 is a long way from 100. In terms of how it improved it its hard to say, it wasn't particularly noisy to start with but hard to say in different places with different signals etc.

[R.G.]

It is extremely likely that your added cap across the power supply was either put in backwards, or not connected where you think it was.

Schematics would help us guess a exactly what went wrong.

There is no good reason a 100uF, or a 1000uF or a 10,000uF cap across the power supply would cut volume if it's really properly put across the power supply and has a high enough voltage rating to not be damaged by the power supply.

[Saturated]

Thanks for the reply, RG it was more of a curiosity for future reference rather than something from a specific schematic. So, the 22 should have worked the same as the 4.7. Probably was backwards.

[nocentelli]

If it was inserted backwards, you are lucky it did not explode. Had that happen to me a while back - Surprisingly loud pop and plume of gaseous electrolyte that narrowly missed my face, followed by  rather acrid stench... you have been warned.

[anotherjim]

Quite a few transistor fuzz circuits are drawn so what looks like a supply dropper resistor is in fact a collector load. Adding a cap to ground there won't be the same as the hoped for power filter. At worse it will kill a lot of signal or at best make a tone change.

[bool]

Ah ... backward caps ... at a recent recap job I messed up and naively/mistakingly put a 2200uF 25V Samwha RD lytic in-backward (because all surounding lytics faced a certain orientation - except for this one).

Disclosure: Samwha RD series contain cocoa-browny goo. The smell wasn't THAT bad though ...

[italianguy63]

^  +1

Yeah the 22uF in a FF is not a filter cap.

[Saturated]

This is the circuit I was playing around with. The cap labelled noise reduction is the one I'm talking about. I am confident I didn't have it backwards. It definitely dropped volume by 70% until I changed it to 4.7.
My question is, if I leave the 4.7 in there, does it provide any "noise reduction" or now useless because of the value.

[thermionix]

Probably was backwards.

I am confident I didn't have it backwards.

If it wasn't backwards, did you measure to see if your voltage dropped?  Might have been a shorted cap.

[italianguy63]

This is the circuit I was playing around with. The cap labelled noise reduction is the one I'm talking about. I am confident I didn't have it backwards. It definitely dropped volume by 70% until I changed it to 4.7.
My question is, if I leave the 4.7 in there, does it provide any "noise reduction" or now useless because of the value.

Yes!  C5 is a filter cap.  47uF or 100uF should be good there...