Fuzz Face trimmer/impedance control: Where in circuit?

[Purplexi]

My ge PNP Arbiter reissue already has three leg holes drilled between the transistors and resistors. I'm just not sure what I'm soldering them to and if 10k - 20k trim pot is enough.

[antonis]

Without picture we are also just not sure what you're talking about..

[darron]

do you mean bias maybe instead of impedance?

[Purplexi]

do you mean bias maybe instead of impedance?

Yes, I guess so...sorry. Not sure. Just want to get this pain in the butt Arbiter reissue to work within it's proper voltages, which I have read is 4.5 to 6v? I purchased a set of resistors to replace the 22k, 1.5k, 47k present with 8.2k, 470ohm, 33k but I have also been advised to add a trimmer at the 8.2k, or the input, I think? Not too good at soldering yet but I'm getting there.

[italianguy63]

The 8K2 is the Bias... you can replace it with a 10K - 20K trimmer...

MC

[Electric Warrior]

do you mean bias maybe instead of impedance?

Yes, I guess so...sorry. Not sure. Just want to get this pain in the butt Arbiter reissue to work within it's proper voltages, which I have read is 4.5 to 6v? I purchased a set of resistors to replace the 22k, 1.5k, 47k present with 8.2k, 470ohm, 33k but I have also been advised to add a trimmer at the 8.2k, or the input, I think? Not too good at soldering yet but I'm getting there.

Some of these had a trim pot on the board, but I don't know where it connects.

A trimmer at the 8.2 is not necessary and it may cause unecessary volume issues. Bias for both transistors can be set with the 33k. The rest is down to transistor selection. Your transistors will probably bias just fine, so you shouldn't worry about bias trim pots yet (but I already told you that in your other thread).

If you're going for stock values, it is necessary to replace the 2k2 Fuzz pot with a 1k or the voltage at Q2's collector will be off.

The voltage range for Fuzz Faces is wider than you're thinking. Vintage Fuzz Faces often measure way over 7V on Q2C. 4.5V is pretty much as low as they got.

[darron]

do you mean bias maybe instead of impedance?

Yes, I guess so...sorry. Not sure. Just want to get this pain in the butt Arbiter reissue to work within it's proper voltages, which I have read is 4.5 to 6v? I purchased a set of resistors to replace the 22k, 1.5k, 47k present with 8.2k, 470ohm, 33k but I have also been advised to add a trimmer at the 8.2k, or the input, I think? Not too good at soldering yet but I'm getting there.

Every resistor in the fuzz face effects the bias in some way. I've done some blind tunings and measurements, and found the 100K and 33K are really well and sensibly set for a nice two transistor fuzz.

The 8K2 isn't necessarily the 'bias' resistor, but it is the one most commonly used to change the bias since it has the most predictable affect for what you're after. That's how I do it. I don't like using a 10k trimpot here since I might often want to try higher values than 10K. A 20k trim can work really well, or a 10K in series with a resistor around 4K7 (so the range would be 4K7 through 14K7).


As Electric Warrior says, changing that 8K2 will also change the volume. If you're worried about low volume, I suggest changing that smallest resistor (3304/470r/whatever is used) to either 1K or 2K (even louder).


I HIGHLY suggest giving this one a read        http://www.geofex.com/article_folders/fuzzface/fffram.htm

[Electric Warrior]

The beauty of using the 33k is that the relationships between the collector voltages will be right. It will bias just like a vintage unit when set in the right range. With the 8k2 you only set Q2C, which changes the relationship between Q1C and QC2.

[Purplexi]

Ya know, this pedal does something I've never encountered in a Fuzz Face. it's dead quiet when I roll off guitar volume. Smooth as an organ pedal. Be nice to know why. Just sayin'. and now that it's cooler early fall, these transistors seemed to have calmed down. This thing is sounding so close, I just need to tap the right trimmer/location? Thanks!

[Electric Warrior]

With falling temperature you get less leakage, which brings up Q1's collector voltage and decreases Q2C. But the good news is that the range of voltages in which the Fuzz Face can sound good is pretty wide.

I guess mismatched transistors may drift further apart with the heat than matched ones, which is why it may sound tamer when it's cold.

Is your pedal slightly gating at the moment? That would explain why it's so quiet. If not, it may simply be the transistors having lower noise.

What's the voltage on Q1's collector currently? As you've already got the 33k in there, that should give us a good estimate on how Q2 would bias with all stock values and wether the bias needs tweaking at all.

Please take a picture of trace side of the board so we can tell you where the trimmer that the board was designed for connects.

[Gus]

This might help to understand the FF
https://www.diystompboxes.com/smfforum/index.php?topic=114153.msg1059002#msg1059002

Pay attention to Electric Warrior posts.

[thermionix]

I leave the Fuzz pot out, and adjust the Q2e resistor to set bias.  1K trimmer + 470 fixed.  Of course the bypass cap still goes straight to ground.  Not saying this is a better method than any other, just another option.  Like the 33k method, it doesn't mess with the output volume.  Since OP has a 2.2K fuzz pot, a resistor or trimmer could be added in parallel with it, this will only lower Q2c voltage though, not raise it.  In my admittedly limited experience, finding transistors that work with stock circuit values, or as close as you can, tends to yield the best results.

[Electric Warrior]

Tweaking the 33k (if necessary) has worked great for me so far. For some transistors I had to increase the value as far as 100k because the they were not leaky enough...

[Purplexi]

This might help to understand the FF
https://www.diystompboxes.com/smfforum/index.php?topic=114153.msg1059002#msg1059002

Pay attention to Electric Warrior posts.

It's not gated at all so it must be the transistors, said to be very good. I will post up a back of board photo when the better phone gets home tonight. Thanks

[thermionix]

What are your collector voltages currently?

[Purplexi]

Please take a picture of trace side of the board so we can tell you where the trimmer that the board was designed for connects.

I know the board looks trashed but it's good for a few more fixes. I'll get a clearer picture up next..

[Purplexi]

[Electric Warrior]

The board is drilled for a trim pot in series with Q1's collector resistor. A 10k resistor and 100k trim pot would probably work well - that is if you need to rebias at all.

What are your collector voltages currently?

We still would like to know your collector voltages to see how it biases with your current setup.

[Purplexi]

 I'll post up later, thanks!

[Purplexi]

What are your collector voltages currently?

With ohm/volt meter set at resistance...positive to base and negative to collector? what kind of numbers am I looking for?