Help my Superfuzz octave!

[Hossymandias]

Hello gurus,

I have a Superfuzz on my breadboard that I built from the schematic at General Guitar Gadgets. The fuzz is totally "there" and everything seems to be working great, except that I'm super disappointed with the lack of octave content. I boarded it after playing through a friend's Shin-Ei fuzz-wah. That thing is a Superfuzz circuit, and it had a great octave up sound.

For a while I thought that maybe modern transistors just don't produce the octave up, but everything I hear on YouTube demos tells me otherwise.

I've used metal 1% resistors, matched HFE on Q4/Q5, and even matched the 10uf capacitors on either side of the octave generator. I'm at my wit's end. Here are my voltages, maybe you all can crack the code...

C          B          E
5.65        .7         .13     Q1
9.49      5.66     5.04     Q2
6.08      3.67     3.08     Q3
1.77      2.03     1.39     Q4
1.78      1.96     1.39     Q5
3.57      1.21       .59     Q6

Thanks!

[LucifersTrip]

There's an octave trimmer that you can use, but first B cannot be > C for Q4/5
C        B        E
1.77      2.03     1.39     Q4
1.78      1.96     1.39     Q5

good voltages from original (Q6C need not be that high):

C        B        E
Q1  6.01    .66      .117
Q2  8.88   6.01     5.41
Q3  6.23   3.27     2.72
Q4  3.1     1.7      1.11
Q5  3.1     1.67     1.11
Q6  5.75   .98       .361

edit (w/ octave trim/balance):

[Hossymandias]

Thanks Lucifer!

I'll look at my circuit tomorrow for any mistakes, but man I've been over that thing a lot. Until then, any ideas why my collectors are so low?

[R.G.]

I'd say that the collector resistor to Q4/Q5 is open or not connected to +V somehow. Bad trace, bad solder, open resistor, something like that. See if the high end of the resistor has +V on it. Could be that there's a wire missing to the top end of that resistor, or a bad/open contact on the breadboard.

[Hossymandias]

I'm so stumped. I came home today thinking I could totally tackle this, but I can't figure it out. I thought the collector resistor was the culprit too, but no such luck. I cannot get the collector voltages up unless I reduce the value of the collector resistor. If i do that, I get the correct voltage on Q4/Q5 but the fuzz sounds all weird, compressed, and strained.

What should be my next step? Should I test all the components that connect to V+? What else could drag down the collector voltage?

Thanks so much for your help. Y'all are amazing.

[digi2t]

What transistors are you using?

[Hossymandias]

P2N2222A-GOSND is the Digikey part number.

[Hossymandias]

The collector current of the 2n2222a is 800, whereas the collector current of the P2n2222a is 600. But this shouldn't matter as long as I am consistent, right? Or does it mean I need to adjust the resistor accordingly?

It is possible that I fried a transistor in my foolings. Maybe I need to adjust the collector resistor so that it is delivering 3v, replace all transistors, and see if that does it.

[R.G.]

I'm so stumped. I came home today thinking I could totally tackle this, but I can't figure it out. I thought the collector resistor was the culprit too, but no such luck. I cannot get the collector voltages up unless I reduce the value of the collector resistor. If i do that, I get the correct voltage on Q4/Q5 but the fuzz sounds all weird, compressed, and strained.

Measure and post the voltages on both ends of (1) the collector resistor (2) both resistors from Q3 and Q4 bases to V+ and (3) both resistors from the bases of Q3 and Q4 to the balance pot, or to ground if you don't use a balance pot.

If you DO use a balance pot, it is possible that the wiper is not grounded, or is open. Now that I think if it, if you do use a balance pot, post the voltage on all three terminals.

It is easier to raise a collector voltage by lowering a base than letting more current through into the collector.

[kaycee]

The superfuzz will work with a wide variety of transistors. I'd does benefit from some fine tuning of them IMO, but you should get a reasonable fuzz from the common suspects.

Tedious as it is, you may need to go through your resistors comparing the bands with what you have in your packs and then measuring others in those packs with your meter just to check that you haven't got a wrong value somewhere. Expect some variation in tolerance, that doesn't matter, it's when you are orders of decades that it's a problem!

I have found that matching the gains of the pair with the meter hfe setting perfectly sufficient to get a good octave, and FWIW I think you get a better octave from 200 or less on this pair, 3904's often suffice.

[Hossymandias]

Measure and post the voltages on both ends of (1) the collector resistor (2) both resistors from Q3 and Q4 bases to V+ and (3) both resistors from the bases of Q3 and Q4 to the balance pot, or to ground if you don't use a balance pot.

If you DO use a balance pot, it is possible that the wiper is not grounded, or is open. Now that I think if it, if you do use a balance pot, post the voltage on all three terminals.

It is easier to raise a collector voltage by lowering a base than letting more current through into the collector.

Okay, here's my voltages.

Collector resistor
V+ = 9.49v
circuit = 1.56v

Q3 base resistor
V+ = 9.49vv
circuit = 3.68v

Q4 base resistor
V+ = 9.49v
circuit = 2.06vv

Q4 base to balance resistor
base = 2.00v
pot = .40v

Q5 base to balance resistor
base = 1.71vv
pot = .39v

Balance Pot
1=.4v
2 = 0v
3 = .39v

[R.G.]

Here's what ought to be happening.

The base strings for both Q4 and Q5 are 100K=>22K=>5K (if the balance pot is in the middle). That makes the base voltage on Q4 and Q5 nominally 9.49V* (27k/100K+27K) = 2.01.

The emitters of Q4 and Q5 will sit about 0.5V lower than the base, so the emitters should be at ~1.5V. That appears across the 1.8K emitter resistor, making the current be 1.5V/1.8K = 833uA. That same current flows in the 10K collector resistor, so it drops 10K*833uA= 8.33V.  So maybe it's doing what it should.

Let's see what ought to be going on to get the recommended 3V at the collectors. That would mean that there's 6V across the 10K collector resistor, and that would be 6V/10K= 600uA. That same current has to flow in the emitter resistor, plus some tiny base current, so there's V = 1800*600uA = 1.08V across the 1.8K emitter resistor. The bases should be at about 1.58, not 2.01. OK, now we know where to go.

Let's say we keep the 100K "top" resistor on each base, and that the bases will be at 1.58V. That means the 100K is conducting (9.49-1.58)V/100K = 79uA. Each base is eating about 600uA/100hfe = 6uA, so we need 73uA to be 1.58V, and that's R = 1.58/73uA = 21.6k. We have 27K with the 22K and the 5K or so contribution from the trimmer pot. 

So the trick is, take about 6K or more out of those 22K resistors. Try replacing them with either 10K, 12K, or 15K. Or paralleling another 22K on each one to get 11K. All of these lower the voltages of both bases, and should raise the collector.

Notice I'm assuming here that you've checked all your part values and have the emitter capacitor inserted correctly, stuff like that.

[Hossymandias]

R.G. you are a true educator. Thanks everyone for your help.

I changed the 22ks to 16.8k and this thing sounds great. I also changed the 100k Q1 base resistor to 15k to get correct voltages on Q1.

I'm happy but confused. Why am I the only one I've heard of that needed to make these changes? I haven't read a single thing about needing to change resistor values to get correct voltages.

I hope this helps someone else.

[Mark Hammer]

R.G. you are a true educator. Thanks everyone for your help.

Can't argue with that.

I changed the 22ks to 16.8k and this thing sounds great. I also changed the 100k Q1 base resistor to 15k to get correct voltages on Q1.

I'm happy but confused. Why am I the only one I've heard of that needed to make these changes? I haven't read a single thing about needing to change resistor values to get correct voltages.

I hope this helps someone else.

Why are you the only one?  Because even within a given transistor number, there are variations, and some folks get lucky.  Incidentally, the diodes are not necessary for the thing to sound good and nasty.  I made one and ended up selling it some time back, and installed a toggle to switch between two different diode pairs and no diodes.  It still distorts and yields octaves without the diodes.  They just up the nastiness a bit.