Fuzz Face (Boutique '69 clone from GGG)

[FirstTimer007]

Hello all !
I have built a Fuzz using the schematic and layout from GGG i.e.

Schematic:
http://www.generalguitargadgets.com/pdf/ggg_ff5_sc_b69.pdf

Layout:
http://www.generalguitargadgets.com/pdf/ggg_ff5_lo_b69.pdf

I bought NPN Ge transistors from Smallbear and reversed the 'polarity protection diode' and the 3 electrolytic caps, and omitted the DC socket - planning on using a battery only.

I first put a pair of 2n3904 silicon transistors in the sockets in order to save from damaging the Ge ones and it worked great with no noise, then I replaced 'em with the germs.

Thing is it worked very well, as quiet as any pedal I've ever used, all in the case, just with some insulation 'under' the board (a blank piece of fiberglass circuit board with copper side 'away' from the circuit), the germanium devices sounded fantastic!

Within an hour it was too noisy to use  White noise and pops and crackles with potentiometer use - I installed the silicon devices again and the noise is there with them also. I have checked continuity with my DMM and measured the voltages on each pin of the transistors which are as follows:

Q1  E  0.00 V    Q2  E  0.74 V
      B  0.60 V           B  1.37 V
      C  1.37 V           C  3.46 V

The battery measures 9.3 V output (brand new).


I don't know what to do next 

Pulling my hair out right now....

My questions are

1.Do these voltages look correct? (Apparently Q2 is supposed to bias around 4.5 V with the resistors supplied by Steve ).
2.Why would it work so well and produce a fantastic fuzz sound, but only for a short time?
3.Can the 'Audio Probe' method be used to debug from here?
4.Can anyone give me some idea of what to do next please?

Cheers Sean

[pinkjimiphoton]

welcome to the fuzzface.
your transistors are gonna change with temperature. and humidity. and the cycle of the goddess. and the stock market. and the tide, and even if ya look at 'em funny. 
germanium can be like that in this circuit. i keep three ge fuzfaces with me at all times when on the job. these ones are pretty un-flakey.
the difference you get just handling them can be astounding.
if you used carbon comp resistors, it could be just moisture making the pops and crackling noises.
but the germanium is a BEAR to deal with sometimes. lights affect them. heat. your breath, even touching them.
what they read at as a gain at small bear may be different from what they need in your climate. if you're colder/warmer/dryer/wetter than they are,
that can influence them.
did you power down between transistor swaps? i like to drain the electro too. just short it to something. sometimes it's easy to damage the transistors.

ok, now all that baloney said, the resistors that you use in a silicon npn fuzzface are slightly different from those in a GE one.
i would suggest comparing the schematics of both and looking less at the transistors and more at the resistors.
RG Keen's The Technology of the FuzzFace at geofex.com is in this case mandatory reading as well.
you WILL figure this out. but i can't give it to ya. you gotta go find it. this forum and google have more opinions and info than the stars in the skys.
read RG's article.
and check to see if your battery is getting hot. if so, you gotta short in your power supply you'll need to fix that too, probably a tiny solder bridge.
noise when turning the pots can happen. if it's a lot, check the coupling caps, their job is to block dc and let the fuzzed audio ac thru.

[JerS]

Here's a shot at answering your questions:
1. these should be fine - 4.5v on Q2 collector is a ballpark target
2. could be a lot of reasons - I would suspect a solder joint, or movement within the enclosure, etc. - or bias drift. Try adjusting the bias pot and see if you can affect the noise. Also make sure the germanium transistor bodies are not touching anything else. Heat shrink them if you can - or tape them off.
3. yes of course! Follow the signal path to isolate where the white noise, etc. is coming from. This is probably the fastest way to isolate where the issue is.
4. retrace your steps - if it was fine before putting in the enclosure, take it out of the enclosure and see what happens. If you are at a loss - get out the audio probe and poke around the signal path. Again, this will probably be the fastest way to isolate the issue.

I hope this helps.

[Electric Warrior]

Here's a shot at answering your questions:
1. these should be fine - 4.5v on Q2 collector is a ballpark target

Right. They're exactly what I'd expect a low gain silicon Fuzz Face to measure.

To get 5V at Q2C you'd need higher gain silicon transistors or germaniums with very low leakage.

welcome to the fuzzface.
your transistors are gonna change with temperature. and humidity.

Is humidity really a factor? I know it's important during the manufacturing process. As transistors are usually sealed with epoxy it shouldn't make much of a difference, should it?

Temperature sure can make all the difference in the world, and the mechanics seem rather simple. Higher temperature -> higher leakage. Hfe doesn't seem to be affected much by this, which makes the voltages in a Fuzz Face rather predictable.
Q1C voltage decreases as the temperature/leakage rises, while Q2C's increases. You can make up for both by tweaking Q1's collector resistor - which is exactly what Arbiter did when they cloned the Tone Bender MK1.5 to create the Fuzz Face.

But I don't think we're seeing a temperature problem here.

2.Why would it work so well and produce a fantastic fuzz sound, but only for a short time?

I guess something broke since you first built it. As the voltages are fine and you're having the problems with two different sets of transistors, I'd look into the offboard wiring first. Maybe tap the solder joints that connect the pots with a pencil to check if they're microphonic...

[EBK]

I bought NPN Ge transistors from Smallbear...

Silly question, perhaps, but does the schematic show PNP instead?

[FirstTimer007]

Thanks for the replies good folk!

I'll try the 'tap with a pencil' and check the off board wiring (why hadn't I tried this?...DUH !!  ) 

My eyes aren't young and sharp any more and I do struggle with the fine soldering sometimes...

Yes the schematic is PNP, but I reversed the polar components (diode and electrolytic caps), hoping that was the way to go with the NPN trannies 

Cheers Sean