Build Your Own Clone Message Board

hi, I finished my fuzz Face, it sounds decent but I get wrong reading for the Q2 collector bias: I get readings from 9 volt to 7.5v with the stock 25k trimpot. do I need a 50k trimpot?

That's what I did... and recommend.

will I be able to do it with two 27k resistors?

I doubt it. You can't dial in two series resistors. I recommend the 50K trimmer because in most cases the 25K doesn't have enough range of adjustment to dial in the collector to 4.5V

can I use a 27k resistor in series with the 25k trimpot?

If you can get it to fit it should work. Once you've added the resistor I'd recommend setting the pedal aside for a while to ensure the transistor is at room temperature before you try to dial in the collector.

Ok, can I just add the 27k to the pin at the middle pin close to the pot?
Thanks BTW

You can add the resistor in series with the wiper of the trim pot or the other pin that isn't shorted to the wiper by a trace on the PCB. Either will work.

I added two 27k resistors to the trim pot - one to the 470 ohm resistor and the other to the .1uf cap

my trimpot only measures 15k this makes it more like 42k.

between ground and q2 I easily get around 5v but between ground and the 470 ohm I still get around 8v
sounds good though

Huh? There is no .1uf pot. The only .1uf capacitor is C2 and it doesn't have anything to do with the biasing of Q3. You cannot measure a resistor or a pot while it is in the circuit and expect to get an accurate reading. You end up measuring it in parallel with the rest of the circuitry.

You only need one resistor in series with the trim pot. There is no need for two. All you are doing is extending the range of the 25K trim pot. You should place it between the trimmer and the collector of Q3 only.

sorry, I meant .1uf cap.
I used both 27k resistors since the trim pot is connected to the Q2 on the one side and the 470 ohm bias resistor AND the .1uf cap on the other side. Instead of taking out the trimpot, I took out one end of the .1uf and one end of the 470

thanks for the help!

OK, I see where I made my mistake. I was looking at the wrong fuzz schematic. At any rate you still only need one resistor connected between the trim pot and the collector of Q2. Get rid of the other resistor.

yes, I agree - I only need a 27k between the trim pot and Q2, but its more convenient to add the 27k on the side where the .1uf and 470 is connected. I'm getting rid of the second 27k btw

What you've done is the equivalent of connecting the capacitor between the trim pot and a 27.47K resistor. What you should be doing is placing the cap between the 470 ohm resistor and the trim pot in series with a 27K resistor. To do that you must place the resistor between the trim pot and the collector of Q2.

I tested with a 100k pot. I needed values from 43k to 75k to get in the right range (4-6v). This is not even close to the included 25k trim pot .
I installed a 33k resistor and a 50k pot, seems to work. but this is NOT what I expect from a 100$ kit that is supposed to include tested transistors and all necessary parts.

the fuzz has too little distortion and output now

If you take another look you'll see that nowhere does it say anything about the transistors being "tested".

If you want more output try replacing the 470 ohm resistor with a 1K.

thanks, I've tried the 1k, I like it but the overall sound is still way weak. the pedal is useless now, it just does not sound right (actually it sounded a little better with the 8-9v bias). and its impossible to get the right bias voltage with the included parts.

are you measurimng the voltage whilst strumming the guitar?

I had similar troubles with the bias. I don't understand why you didn't just replace the 25k with a 50k or even a 100k trimpot - you've really gone around the houses with this one, no wonder you're having output problems with all the unnecessary fiddling you've done.

Something else to try - swap the transistors over. The whole point of "tested" transistors is that the one with the lowest gain goes in Q1 and the highest goes in Q2. If that doesn't work, try putting something like an OC140 in Q1. I did this and got 4.5v with room to spare on a 25k pot while keeping that classic germanium fuzz tone.

The fuzz face is a notoriously fussy circuit. It may be easy to build but it's quite hard to optimise, and that's not really a fault with the kit (though it would be nice if the transistors came in matched pairs).

if you read my post, you might see that it sound weak with a larger value resistor. also, I didn't have a 100k trimpot available and the 50k was to small.

byoc have sent me new transistors and a new trimpot. gonna try them next week

Did you try swapping over the originals?

yes, if I remember correctly I did and it didn't help much.

I still have some strange problem: the voltage at the other test point, the 470 (1k) ohm resistor is always about 9 volts. according to the instructions this voltage should be 4-5ish volts. also the voltage a Q2 is still to high.

with a 33k resistance instead of the 25k trimpot I got it to sound good at one point but output is generally weak. I have to turn both pots fully up

Its starting to sound really good with the new transistors. specs:
50k trim pot
470 replaced with 1k for output
2.2uf replaced with .1 for cleaner bass
.1uf replaced with .01 for less and clearer bass
2200pf bright cap on volume for more gain, cut and articulation

I didn't care for the 2k fuzz pot

added external bias pot and germanium diode btw base and ermitter on q1