Fuzz Pedal Problem

[makoto12]

I don't know if anyone can help me with this or not, but i figure it's worth a shot.  I have a hand built germanium fuzz pedal (standard fuzz face circuit) that went dead recently (i think because it got too hot at my practice space and killed the transistors).  I sent it to the builder (who agreed that that's what seemed to be the problem) to swap out the transistors, which he did.

My pedal line looks like this - Guitar (Les Paul) > Tube OD pedal (always on) > germanium fuzz > MXR Micro-Amp boost > Memory Man Delay > Fender Twin Reverb.  I used to be able to dial in a volume on the fuzz that was pretty close to my normal volume, and then i would use the Micro-Amp (a pretty standard clean boost - although it does add a bit more to the treble) to either boost my "clean" or fuzzed sound accordingly.  Now, and here's my problem, what happens is that the fuzz sounds a bit muddy and quiet (without the Micro-Amp on) than I think it used to, so I have to turn up the volume on it to match my "clean" sound, but when I switch on the Micro-Amp, it boosts the fuzz far more than the clean (and actually makes it sound more clear, less muddy - more like i think it should).  So in other words, I used to be able to boost both "clean" and fuzz signals about the same when the MXR is on, but now the MXR boosts the fuzz like 10 times what it boosts the "clean" (actually, it seems more like the fuzz doesn't perform enough until the MXR "pulls" the signal out of it), so even on the lowest setting, the MXR makes the fuzz sound much louder than when the fuzz is off.

Any idea on what would cause the pedal to do that?  I'm just a novice when it comes to these pedal electronics, but i have been learning a lot the past few weeks in trying to fix this.  I've tried swapping out the transistors again with a new matched pair (with sockets) that i got from small bear, but it didn't seem to make a difference for this problem.  So now I'm thinking maybe it's the caps or resistors(?).  I can solder well enough, so I don't mind swapping out parts or anything - I'd just like to know if that's the right path before I spend more time and money on it.  The board has the two standard FF Electrolytic caps (2.2mf and 22mf), but i can't figure out what the other (green) cap is based on the number on it - 1H103KT (and i'm pretty sure that's what gives this pedal the tone that i love.  i can't find another pedal that sounds like it).  The resistors look to be 33K, 510 ohms (not standard FF), 100K, and 8.2K.

Any suggestions would be welcome.  Thanks a lot!

[Fret Wire]

Maybe I reading this wrong, but it seems your FF isn't biased right. All was well before your fuzz died, right? You got it back, and now you have this problem. Am I correct, that all by itself, the fuzz no longer sounds good?

That, and the fact that it has stock collector resistor values (33k & 8.2k), seem to point to misbiased transistors. The standard Dallas ckt values rarely seem to bias up correctly with most transistors.

If you have a DMM, measure the transistor lead voltages for both Q1 & Q2, then post them here, along with your battery voltage.

The cap in question (103), is .01uf, standard Dallas value.

[petemoore]

First of all your'e doing well to use sockets, otherwise heat sinks should be used when soldering transistor leads.
 Last time I bought a set of Ge's from Small Bear, they came with documentation and bias resistor values. Insert these values in your FF, and the SB transistors should work and bias correctly.

[makoto12]

You are right - it sounded good before the new transistors.  Now it only sounds really good when the Micro-Amp is pulling the signal out of it.

I don't have a multimeter - i suppose i could go buy one, they're not too expensive.  I'm still figuring all this stuff out, so bare with me.

Yeah, i believe small bear did include the bias values.  I'll find those and post them later.  So, if I understand right, i should just need to change the resistors to adjust the bias, right?  I did tell small bear the resistor values before he sent the new transistors, so i imagine that they were matched to those.  (I could be wrong about the 510 because the band colors are faded and kind of hard to make out, but i think that's what it is.)

[Fret Wire]

You'll adjust the bias with the 8k2 and 33k resistors. Use the resistor values Small Bear gave you, and it should sound much better.

The 510ohm resistor should be 470ohm. That difference is not a big deal, though.

If you're going to do much more DIY work, a DMM is very helpful to have.

[petemoore]

First thing I did when I recieved my Second set from SB, is MARK Q1 Q2 and in this case Q3 [tonebender].
 But my DMM has a transistor Hfe checker, [doesn't tell leakage] which I can use to measure the low leakage SB transistors so I get the low gainer in Q1.
 The papers you recieved will have like: R1 [which relates to the schematic R1] then something like 47k...use whatever R value specified for the component R1. Repeat for all the resistors listed on the paper.
 You should be biased, use ROG's FF transistor pin voltage listings for reference [the one with Ge's], your's should be ssomewhere in that ballpark.
 Then, if you have a multimeter and pencil tip iron, perf up a Multi Face or other tunable FF derivitive, and swap [C's R's Q's...] 'till you drop!!!

[b_rogers]

if i read correct you are running a tube od pedal before the fuzz?

i know my fuzzes like to be first in line...try switching the order of the fuzz and tube od...couldnt hurt


Brent

[makoto12]

i've tried putting the fuzz first, but it didn't seem to make a difference.  and since it used to work in this order, i'm pretty sure it's something else.  most of the fuzzes i've tried seem to be OK being behind just that one pedal, and it's always on (it has EQ too, that i use it to shape my signal, so putting the fuzz first changes the sound quite a bit).


the small bear papers did say 470 for that one resistor, so i'll try swapping that one.  just curious - does anyone know what changes in the sound would occur with a 510 ohm instead of 470, and vice versa?  i'm just wondering what effect, other than possibly fixing this gain problem, changing that resistor might have.  maybe i'll just stick a socket on there too so i can experiment with a couple different values (gotta love that experimentation).  what other values can i try for the 8.2k and the 33k to adjust the bias?

[Steben]

if i read correct you are running a tube od pedal before the fuzz?

i know my fuzzes like to be first in line...try switching the order of the fuzz and tube od...couldnt hurt


Brent

This only matters if there is a buffer in the Tube OD right?
If FF is placed first it "uses" the high impedance of the guitar to reduce the highs, giving some milder distortion. If all is true bypassed, the FF should sound the same.

[Fret Wire]

the small bear papers did say 470 for that one resistor, so i'll try swapping that one.  just curious - does anyone know what changes in the sound would occur with a 510 ohm instead of 470, and vice versa?  i'm just wondering what effect, other than possibly fixing this gain problem, changing that resistor might have.  maybe i'll just stick a socket on there too so i can experiment with a couple different values (gotta love that experimentation).  what other values can i try for the 8.2k and the 33k to adjust the bias?

The 510/470ohm change is going to be small. What values did Small Bear give you for the 33k/8.2k resistors? They are the important ones for biasing. If you don't have the values, that's where a DMM is vital. Giving you advise without the transistor lead voltages, is like driving at nite without lights. You could try raising/lowering the 8k2 a small amount, and note whether it sounds better or worse. Which ever way it sounds better, go in that direction until it starts to sound bad again. Check the Small Bear sheet again and get back to us.

[petemoore]

"Tag a pot in there to set the bias"...an alternative...
  lift one end of the resistor from the board, and connect the wiper of a 20k-47k pot to the other end. Connect either outside luf of the pot to the board where you lifted the resistor, to the board.
 Connect DMM to ground, and set collector of transistor to desired voltage.
 Without changing the setting on the pot, lift [disconnect from connection] one [or both] of the pots connection and measure the resistance with the DMM.
 Replace that resistor with a close value to the resistance read on the  pot.
 two 10k parallel = 5k
 two 10k seriesed = 20k
 you can build hard to find resistor values using resistors in parallel or series or both.
 two 10k parallel = 5k...add a 2,2k to that and you have 7.2k...
 See what 8k2 and 15k parallel reads just for kicks [replace any of these values for this test].