lm386+preamp loud buzz...

[artsinbloodshed]

Hey guys.
Because I test all my fuzzes on my noisy cricket (with some really good surprises sometimes!)
I've decided to build a "noisy cricket" and implement a fuzz circuit (fuzz face type) instead of the mpf 102 buffer in front of the lm 386.
thus, I have a preamp and an amp running at 9v.
But I have a prob...It squeals/buzzes as hell, depending on the volume fed in the lm 386 or the distortion of the fuzz
It stops squealing at an almost inaudible volume...
after having done some mods/comparisons and all, i've figured out that each circuit is fine and works perfectly separately...
everything comes from that they share the same 9v plug.
separately (diff dc plug) they're fine and work like a charm, but sharing the plug and bam, the buzz...
just to try something:
I've set a pot to control the volume fed in the lm with no more luck
I've put 1n914 diodes on each cords feeding each circuit with no luck either (there could have been some kind of feed back).
tried to rise the value of capacitance of the cap to ground at the dc plug (100uf>220uf>up to 940uf). the squeal/buzz changes the pitch or reduces slightly.

Does anyone have an idea?
Thanks guys!

[artsinbloodshed]

And of course, i've swapped the power supply to verify if it could have been the source...but nope.
No ideas?

[Davelectro]

I'd try a low value resistor in series with +V (followed by a cap to ground) between the lm386 circuit and the FF.

[artsinbloodshed]

What do you mean by "between"?
If i follow you, i should try like a 47 ohm at the v+ with a cap to ground (let's say 100uf/200uf) for each lm386 and fuzz circuit...double team?
-v+>47ohm>cap to ground>fuzz
-v+>47ohm>cap to ground>lm386
?

[Davelectro]

Take a look at some amp schematics and how different stages are decoupled from each other at the power supply rail.

I think 47 ohm it's ok.

Pay attention to ground layout/wiring, too.

[artsinbloodshed]

I've search for amp exemples concerning decoupling. Nice tip man. Thanks.
Got an "humble" schem and it's quite obvious how they decouple.
I'll try to do that right away!

[tca]

...I have a preamp and an amp running at 9v.
But I have a prob...It squeals/buzzes as hell, depending on the volume fed in the lm 386 or the distortion of the fuzz
It stops squealing at an almost inaudible volume...
after having done some mods/comparisons and all, i've figured out that each circuit is fine and works perfectly separately...
everything comes from that they share the same 9v plug.

It is nice you mention that, I've the same similar problem.

Cheers.

[artsinbloodshed]

hey TCA!
obviously misery loves company!
yeah,pretty annoying hu?
Didn't have the time to try out the resistor in series+decoupling cap for each part of the combo preamp/amp yet...
I've previously tried with other circuits though,like an omnidrive.
big buzz and all.
the funny part is that I could get rid of the buzz by putting a resistor in series after the volume of the omnidrive (feeding the lm386) to make the volume pretty low, and rectifying it with a clean mosfet booster.
Let me tell you that it's not electronics but some kind of sorcery instead...I hae no idea why it worked... yet!

[artsinbloodshed]

Just to post a little update for those whom might be curious...
I've managed to get rid of the buzz/hum/thingy by soldering a 220R in series (after Vcc) and double the cap to ground (100uf+100uf) for the preamp section.
It needs to be refined though, the squeals comes back at 100% distortion settings from the fuzz preamp...