Please check these measurements on my FuzzFace clones.

[Burstbucker]

I just built a couple of FuzzFace clones and I've got them set up to read appx.-4.5volts on Q2's collector but apparently I need to be concerned about the voltages in other areas of the circuit, or so I've been told anyway.

The first fuzz has a pair of NKT275 Germanium transistors, I used GEO's gain testing method and came up with Q1=65hfe and Q2=70hfe.  As for resistors, in R1 I've got the standard 33k, R2 is the standard 470 ohm, R3 is a resistance of 5.25k, and R4 is the standard 100k.  
The voltages read as follows...

Q1 base= -0.14V
Q1 collector= -0.96V
Q2 base= -0.96V
Q2 emitter= -0.78V
Q2 collector= -4.8V


The next fuzz has a pair of Germaniums that I got from Small Bear and according to Steve Daniels Q1=89hfe and Q2=141hfe.  The resistors are as follows......R1=39k, R2=470ohms, R3=6k, R4=150k.
The voltages read as follows...

Q1 base= -0.14V
Q1 collector= -0.94V
Q2 base= -0.94V
Q2 emitter= -0.8V
Q2 collector= -4.5V


BTW, both Fuzz pedals sound great IMHO, I was just wondering about these different voltages, if they're pretty much in line with a good old original FuzzFace?  Do these numbers look ok?

[petemoore]

I just built a couple of FuzzFace clones and I've got them set up to read appx.-4.5volts on Q2's collector but apparently I need to be concerned about the voltages in other areas of the circuit, or so I've been told anyway.

The first fuzz has a pair of NKT275 Germanium transistors, I used GEO's gain testing method and came up with Q1=65hfe and Q2=70hfe.  As for resistors, in R1 I've got the standard 33k, R2 is the standard 470 ohm, R3 is a resistance of 5.25k, and R4 is the standard 100k.  
The voltages read as follows...

Q1 base= -0.14V
Q1 collector= -0.96V
Q2 base= -0.96V
Q2 emitter= -0.78V
Q2 collector= -4.8V
 >>>{I think the Q2 B/E voltage difference needs to be larger]


The next fuzz has a pair of Germaniums that I got from Small Bear and according to Steve Daniels Q1=89hfe and Q2=141hfe.  The resistors are as follows......R1=39k, R2=470ohms, R3=6k, R4=150k.
The voltages read as follows...

Q1 base= -0.14V
Q1 collector= -0.94V
Q2 base= -0.94V
Q2 emitter= -0.8V
Q2 collector= -4.5V


BTW, both Fuzz pedals sound great IMHO, I was just wondering about these different voltages, if they're pretty much in line with a good old original FuzzFace?  Do these numbers look ok?

[Fret Wire]

I just built a couple of FuzzFace clones and I've got them set up to read appx.-4.5volts on Q2's collector but apparently I need to be concerned about the voltages in other areas of the circuit, or so I've been told anyway.

You were asking about this on Fuzz Central, right? First, the other voltages are important for troubleshooting, seeing 0v on Q1's collector is always a relief, lol. Also, they can give a clue if your trannys have high leakage.

Back to your question, you can bias your fuzz by adjusting the collector of Q1 alone, Q2 alone, or by adjusting both. And even if Q2's collector reads 4.5v, the other voltages will be different with each method. One way usually sounds better than the rest. Sometimes, one method of biasing will sound about the same as the others, but clean up better with the guitar volume.

Your voltages are proper, proportionally. Q2's collector should start out at about half battery supply (not always 4.5v), and can go about 1v either way. Q2's base should be around .1v higher than Q2's emitter. Q1's collector is usually about .4-.5v higher than it's base. Q1's emitter is 0v. These are approximate voltages, if the proportions are correct, the trannys will at least work.

I try to get around the following voltages:
Q2 C: 4.5-5.5v
B: .5v
E: .4v

Q1 C: .5v
B: .1v
E: 0v

I usually get the most dynamic sound around these voltages. I don't automatically set a fuzz at these voltages and leave it though. Ge's being what they are, I try all three biasing methods to get in the ballpark, fine tune, and see which biasing sounds the most dynamic.


http://diystompboxes.com/sboxforum/viewtopic.php?p=203627#203627
Look at the voltages on that thread. Joe's calculator biased Q2's collector  too high, but the other voltages were right on for what I normally bias them at. Although they sounded better at 4.5-5v, they still sounded real good at 5.5v. Not bad for a plug n' play Fuzz Calculator!

The voltages also depend on the trannys. This is kind of related to a recent thread on AC128's. It's not all just the numbers of gain and leakage that make good fuzz transistors. It's also the stability in the working ckt.  Whether you use RG's or Steve's method of testing, you'll see the same pattern if you test enough transistors.

At first the leakage will slightly rise, then start to drop. This is normal due to the heat from handling increasing the leakage slightly. Then, within a minute or so, a good pair will stabilize, and hold solid at a certain gain and leakage reading. If they are the proper range gain/leakage wise, and biased right, they will sound great no matter if they are OC's, AC's, 2N's, or what ever.

What happens alot with many transistors, especially with AC128's and OC75's in my experience, is when you go to test them, they have the usuall leakage fluctuations due to handling temps. But, what happens different is that they never stabilize. They look like timers, the leakage keeps dropping for minutes, and never seems to stabilize. If they measure say 125 gain/100 leakage when you first put them in your tester, 5 mins later they are at 75 leakage and still dropping (more slowly). Because leakage and gain are proportional, if you measure them initially, and 5 mins later, the gain will be roughly the same. These are the trannys that you think are ok, but don't show good proportional bias voltages, may sound good, but never great. Many times these type of pairs won't clean up well with the guitar volume. It's similar to a "life test" for tubes. A tube may pass for emissions and leakage, but fail a "life test", indicating that although it met specs, it will probably fail shortly under real ckt operating conditions.

Probably a lot of these transistors being sold around as good, matched pairs. If they are going strictly by the gain/leakage numbers, they aren't lying. That's why its better to get matched pairs from Steve or other reputable sources.

BTW, both Fuzz pedals sound great IMHO

That's the real bottom line. Does it sound dynamic and clean up well? If it does, leave it alone...you're done.    Build your next fuzz with trimmers or temporary pots and experiment away. You'll see what I meant. With Ge's, they are so variable that in the end, if it sounds good...it is good. The rest is all useless drivel. Not every good pair of Ge's is going to bias up to a magical set of voltages.

[Fret Wire]

Here's the short version....there's more than one way to skin a cat, bias wise. Don't feel locked into the "adjust Q2's collector at 4.5v, and you're done" method. And follow a solid approach when building a fuzz. Good, stable transistors, right gain/leakage, and proper biasing. Then if you don't like the eq, try different input/output caps. Brett and others have posted nice fixes for oscillations and fizziness. Just don't jump to these right away because it doesn't sound right. Find out why first. Get your bias set the best it can be for your transistor combo, then you can accurately tell if you need EQ adjustment or the other fixes.