Neg Gnd FF Questions

[Curt]

I just finished wiring up a Neg Gnd FF last night.  Got the Ge's from SmallBear, PC board from JD Sleep, and I really expected it to sound great.  Nope...sounded compressed, mushy and when I turn the volume down on my strat, at about 3 it starts to oscillate.  The further down I go, the lower the frequency.  I've reviewed some postings here, and it seems the neg. gnd. version is just not what mother nature intended.  So, tonight I'll rewire it to pos gnd.  My questions are: (1)Should I even wire in a plug for external power?  It seems you would have to use an isolated supply if external power was used?  Plus it seems from the schematic that the battery is actually part of the circuit. (2) I have a 3PDT switch in it now, and would really like an LED in it...any reason I can't put an LED setup on the 3rd set of poles?  Power drain?  Added impedence?
Thanks!

[Fret Wire]

There's no difference in sound between the two grounding schem's, but yes, once in awhile, an NPN ground fuzz can have problems. Before you do anything, first check the voltages on Q1 & Q2 with a DMM. You may be just misbiased, that's all. In the Fuzz build notes, JD lists some baseline voltages to shoot for. If the bias checks out ok, and nothing else seems to be wrong with your soldering or wiring, try switching it over. Remember to give everything a good double check before you decide it's a grounding issue.

No real need for you to go with a power supply, the fuzz face has a long battery life. Use one of the wiring options JD lists on his site. Scroll to the bottom of the link and you'll see an option for 3PDT, LED, and battery only.
http://www.generalguitargadgets.com/v2/index.php?option=html&file=instructions/switching_all.htm&Itemid=51&op=page&SubMenu=

[R.G.]

I tell you three times:

Wiring a positive ground designed effect like the fuzz face for negative ground can result in oscillation, sometimes intractible oscillation.

Every time one of these situations has come up here and the builder changed to positive ground, the oscillation quit.

That doesn't mean you can never use negative ground on one of these and get away with it, but that's just what happens - you get away with it. People seem to think that if it works once, it will always work. That is not the case.

There are two kinds of negative ground FF builders - those who have had oscillation, and those who have *not yet* had oscillation.

In my opinion, building a negative ground FF is not a suitable project for a beginner who will be baffled when it doesn't work, and should not be presented as such because a beginner will not know what to check and how to cope with the problems.

[petemoore]

Jumpin in...waters fine...
 PNP Pos Ground ...or...
 Neg ground...I hope you know what you're doing, cuz I don't...know what makes these work, or, in most cases, not work.
 I have read 'wired correctly / no good' results repeatedly for the Neg Gnd PNP FF

[Chris R]

I worked on my negative ground FF for about 6 months.  I built and rebuilt a few times all with the same 0 guitar volume oscillation.  Save yourself some time and go with the positive ground.

C

[Curt]

Well, I rewired it to positive ground and re-biased Q2 by adjusting R5 so that I had about 4.5 volts collector voltage and walaa!  It works and sounds just fine now.  Regards to R.G., he is ABSOLUTELY right.  Not only does it not oscillate, but it SOUNDS correct!