Nasty Fuzz Face noises

[1wahfreak]

I'm going around in circles trying to cure a nasty noise I get in my newly built FF. When using a 9V battery, I get a really horrible sound (sounds like a idling Harley). This only happens when I use the battery supply and when my guitar and FF volume are turned all the way up. If I turn either one down to about 9 or so, the nasty noise clears up, but then it gets really blatty and gated sounding. I'm using really nice non-leaky (~30 micro amps) Mullard OC-42 trannies. I've measured the input voltages using the regulated supply and the 9v battery and I get ~9.15 for both.
Again none of this happens when using the Voodoo power supply. I'm using all the componants spec'ed out on Fuzz Centrals site and a premade board from G.G.G. It's a PNP negative ground. The only thing I can see different between the 2 sites is that Fuzz Central calls for a .01 input cap and G.G.G calls for a .1. Could this be the problem?

[idlefaction]

i had this exact thing on the weekend!!!!!  i pulled the whole board to bits and redid it with all metal film resistors and bypassed the electrolytics with 0.001uF ceramic caps, 0.1uF poly film output cap, and it still motorboated.

fresh battery changed the pitch of the motorboating, but it was still there.  if i bypassed the supply with a 220uF cap, it went away, but i couldn't fit the board in the case.

in the end i tried wiring it positive earth (it was negative) and that made the motorboating go away - mystified!

[1wahfreak]

Our E.E. at work said that putting a large ceramic cap (in parrallel with the battery??) may fix the problem but he wasn't sure. This is my first time building anything like this and it seems like such a simple circuit. I've done plenty of reading and research and have rebuilt this thing 3 times already (at least I'm getting better at wiring). I figured that if people are making premade boards and componant lists for such an easy circuit that it is probably something I screwed up.  Glad to know it's not just me. I really wanted to keep it negative ground so I can use my power supply. There has to be an answer somewhere.  Were the originals negative ground?

[gez]

if i bypassed the supply with a 220uF cap, it went away, but i couldn't fit the board in the case.

in the end i tried wiring it positive earth (it was negative) and that made the motorboating go away - mystified!

When you use the negative rail as ground for a PNP trannie, the input signal 'sees' the internal resistance of the battery in series with the emitter.  Bypassing the supply with a large value cap(10u-100u is common) provides an alternative path which is often of lower resistance.

It sounds as though the internal resistance of the battery is causing a problem here, especially as it gets flat as it will increase.  Mains adapters usually have very low internal resistance and it's constant which is why they're a better option if you're not going to use a bypass cap.

I use positive ground with NPN/conventional circuits all the time.  It's always a good idea to sling a large value cap across the rails, 10u-100u usually does the trick.

[RobB]

Boy am I glad I stumbled across this thread!  Yesterday I finished my Fulltone 69 clone.  When tested, I found that although I could get a signal through it, it would motorboat on some settings.  I built the Negative ground version so it could be used with other pedals without requiring a separate plug pack.  Schematic at this address. http://www.generalguitargadgets.com/v2/diagrams/fuzzface_b_sc_pn.gif
I spent hours going over this thing with a multimeter and couldn't figure it out.  Putting a largish electro across the positive and switched gnd cured my problem.  Thanks for the info.

This -ve Gnd PNP / +ve Gnd NPN / Extra large capacitor thing should be put in a Fuzz Face FAQ somewhere.

[1wahfreak]

I finally got mine to work too. I put 100 uf cap across the supply but it still didn't fix the problem. Maybe a 220 would have one the trick but I didn't have one available. I finally wired it positive ground and it works just fine now. This is obviously not just a problem I have encountered. I would assume that everyone who builds a FF from GGG would have this same problem. I was going to build the Boutique FF from GGG also and for now I think I will just use positive ground to save myself the frustration. Does anyone know if there a different way of negative grounding that would eliminate the problem?

[Paul Marossy]

Hmmm.... that's interesting that you have had all those problems. I built a negative ground Boutique Fuzz Face about a month ago, designed my own PCB layout based on the schematic at GGG, and had absolutley no problems at all with my circuit. I suppose it may have to do with the fact that I am using a Boss wall wart power supply with a parallel connector cord... although I think I tested it with a battery and had no problems with that, either.

[elehvantti]

I have exactly the same problem with a GGG negative ground PNP Boutique Fuzz Face! Horrible motorboating at some settings and when the guitar volume is rolled down. And this is only with battery power - connecting the circuit to a 9 volt adapter helps.

Guess it's just the way negative ground FF works - just as gez explained above. And yes, this thing really should be in a FAQ!

Oh well, time to do some re-wiring. :roll:

antti