fuzz face issues....

[arielfx]

hey everybody!!!

i just built the fuzz face from GGG and when i turn down the volume on my guitar i hear a strange squeeling noise. this happens only when the fuzz is set to the max. i used matched ac128 i had around.
i dont know where else to turn so i came here? any ideas about fixing this?

thanks!

[petemoore]

Yes, is it a neg or a pos ground circuit.
  about half the time or less Pos ground works 'right' conversion from pos to neg ground circuit is fairly common and only requires the  polarized cap and power supply polarities be reversed.

[arielfx]

hey,

i think it is negative ground

http://www.generalguitargadgets.com/diagrams/fuzzface_lo_pn_3pdt.gif

[cd]

That's normal with a PNP circuit wired for negative ground.

[arielfx]

so i should replace the power supply polarity + polarized caps + transistors orientation?

[cd]

so i should replace the power supply polarity + polarized caps + transistors orientation?

You mean turn it into positive ground?  If you want to get rid of the squealing, yes, but then you're forced to use battery power unless you have the proper (uncommon) adapter or a fancy power supply.

[arielfx]

is there anything else i can do to fix the squeeling problem?

[cd]

is there anything else i can do to fix the squeeling problem?

Nope.  Actually I don't remember offhand, but it's common (and normal) for effects that are PNP wired to negative ground to squeal.  Try a search, R.G. has commented on this a thousand times.

[arielfx]

so next time i should build the NPN version huh?
by the way i just looked at my power supply and i can change the polarity so that should work just fine if i change the effect to positive ground right?

[RedHouse]

cd
That's normal with a PNP circuit wired for negative ground.

Well that's not always true, having a few dozen FF's under my belt I am of the opinion that usually the transistors causing the oscillation issues can be stabilized without reorientation of the ground scheme.
(all construction issues aside of course)

Although many builders, and DIY gods alike, report that just changing from Neg-to-Pos miraculously heals their FF, I've experienced much different results after buiding my FF testbed "jig" board.

I made the testbed jig for determining bias resistor values, cap and other component mods on my FF circuits, the jig is a fully adjustable FF with trimpots replacing all resistors, sockets for the transistors and all caps, test points in the appropriate places, and... a power polarity switch for testing/applying the Pos-vs-Neg theory.
(though I don't need to the switch anymore)

Anyway, using the switch to change the circuit from Neg-Gnd to Pos-Gnd has proven ineffective for me, every time, at healing the circuit, a when it howls, it howls either way.

On the up-side, through experimentation I've found the fix(s) to be quite easy, most often just adding an input resistor to the base of Q1 of around 16k-25k will do it, if not then add a 50-100pF cap across the base and collector of Q2 that works really well. Using one or both of these fixes I've been able to stabilize every FF I've built (so far) without regard to wether it's a Negative or Positive ground circuit.

[arielfx]

thank you very much for the help... adding a resistor and or cap. will be much easier!

[fuzz_fanatic]

i have the same problems!

[arielfx]

redhouse - tried them both. the cap did not help and the resistor made the fuzz stop working (no sound coming out). i changed the transistors but no luck with that either.

[petemoore]

IIRC, This is necessarily so:
 PNP POS ground FF's, when wired up, work.
 PNP NEG. Gnd. FF's have a long history of problem [ x y and z ] posts.
 And...reports that they don't actually work the same as a 'FF'.
 A pos Gnd FF, PNP has appeal in the text, however I've never had issues with them...course I stayed away from them too...lol.
 reversal of polarized items is what it takes to convert:
 Power supply, and polarized capacitor - and +  get inverted, that's all.
 I run my pos Gnd FF in an externally insulated box.

[arielfx]

my FF clone is negative ground... i understood that if ill convert it i can forget about any power adaptor.
so what should i do to keep it neg. ground but not making noises when i turn down the vol. on my guitar?

[petemoore]

cd
That's normal with a PNP circuit wired for negative ground.

Well that's not always true, having a few dozen FF's under my belt I am of the opinion that usually the transistors causing the oscillation issues can be stabilized without reorientation of the ground scheme.
(all construction issues aside of course)

Although many builders, and DIY gods alike, report that just changing from Neg-to-Pos miraculously heals their FF, I've experienced much different results after buiding my FF testbed "jig" board.

I made the testbed jig for determining bias resistor values, cap and other component mods on my FF circuits, the jig is a fully adjustable FF with trimpots replacing all resistors, sockets for the transistors and all caps, test points in the appropriate places, and... a power polarity switch for testing/applying the Pos-vs-Neg theory.
(though I don't need to the switch anymore)

Anyway, using the switch to change the circuit from Neg-Gnd to Pos-Gnd has proven ineffective for me, every time, at healing the circuit, a when it howls, it howls either way.

On the up-side, through experimentation I've found the fix(s) to be quite easy, most often just adding an input resistor to the base of Q1 of around 16k-25k will do it, if not then add a 50-100pF cap across the base and collector of Q2 that works really well. Using one or both of these fixes I've been able to stabilize every FF I've built (so far) without regard to wether it's a Negative or Positive ground circuit.

[arielfx]

ya, i did that
didn't help...

[B Tremblay]

the resistor made the fuzz stop working (no sound coming out).

How did you place the resistor?  Adding series resistance at the input shouldn't kill the sound.

[petemoore]

ya, i did that
didn't help...

I'm sorry...'which 'that' did you try ?

[brett]

what should i do to keep it neg. ground but not making noises when i turn down the vol. on my guitar

This is a common problem.  I believe that it is background radiation (ie same as between radio stations) from the big bang  :shock: .
Try placing a 0.001uF cap between the input and ground.  Let us know if that works.  Also, a 100pF cap between the base and collector of Q2 helps elimate RF interference.
cheers