Biasing a FuzzFace
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When biasing a Fuzface that has a bias trim pot, do the controls (Vol, Fuzz) need to be set full ccw?
- DrNomis
- Old Solderhand
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Frostbite Slim wrote:When biasing a Fuzface that has a bias trim pot, do the controls (Vol, Fuzz) need to be set full ccw?
I've found that it actually doesn't really matter where you set the Fuzz and Volume controls when setting the bias....
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- guitarmongot
- Breadboard Brother
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VERY interesting read....Thanksguitarmongot wrote:Here´s some interesting reading :
http://www.physics.mcgill.ca/~grant/Stuff/fuzzface.txt
/cheers M
- soulsonic
- Old Solderhand
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That's actually, a really poor way of doing it. The best way to bias a Fuzz Face (or Rangemaster) is to have a single trimmer for the Emitter resistor on the second stage. Instead of using the Fuzz control as the Emitter resistor, use a trimmer, and wire the Fuzz control as a variable resistor in series with the bypass cap (the one normally connected to its wiper). Or, use a slightly higher value for the Fuzz control (try 2k or 5k) and have it wired normally with a trimmer tacked on in parallel to it. 5k is usually the best value for the trimmer in any case. Adjust the trimmer so you get 4,5v at the Collector of Q2, and you're in business. The bias should end up being fine for the first stage as well, only time it isn't is when there is too much of a difference between the gains of the two transistors. But they don't have to be matched exactly for it to be right, just in the same general ballpark.Frostbite Slim wrote:VERY interesting read....Thanksguitarmongot wrote:Here´s some interesting reading :
http://www.physics.mcgill.ca/~grant/Stuff/fuzzface.txt
/cheers M
If you follow the advice of that article and replace everything with trimmers, you end up with them all "fighting" each other as you adjust it. Adjust one and it gets about right, start adjusting another, and then it's all off again... makes it way more complicated and messy than it needs to be. Also, the tone of the circuit can change dramatically when you change the value of the Collector load. Collector resistors should NEVER be used for bias trimming. Only time it's acceptable to have adjustable Collector loads is when you're intentionally wanting to have a thing that changes the tone of the circuit.
"Analog electronics in music is dead. Analog effects pedal design is a dead art." - Fran
- guitarmongot
- Breadboard Brother
Thats interesting SoulSonic. For Rangemaster typ boost I find biasing with 5K trimpot on emitter is a great way (just as you describe).
For FF I broadbend classic stock values with trimpot on Q1 C (33K) and Q2 C (8.2K) and trim on 330 or 470 ohm (2K trim).
I go for 4.5V (or -5.5V for GE) on Q2C and 1-1.3V on Q2 C.Then I turn down guitar vol to 7 and fine tune trimmers for clean tone.
2K trim I set max output vol for FF. I usually have 2Kpot at 90% setting and 100 ohm in series for 22uf cap for Fuzzpot).Then I have a pair of FF trannies with fixed resistor values...
I know thats a lot of trimmers to adjust but usually your really close to stock values if you go for (80-120hfe GE ) and 250-300 hfe Si .
This weekend I will try your method of adjusting Q2 emiter on a FF : never tried that before should be fun...
/cheers m
For FF I broadbend classic stock values with trimpot on Q1 C (33K) and Q2 C (8.2K) and trim on 330 or 470 ohm (2K trim).
I go for 4.5V (or -5.5V for GE) on Q2C and 1-1.3V on Q2 C.Then I turn down guitar vol to 7 and fine tune trimmers for clean tone.
2K trim I set max output vol for FF. I usually have 2Kpot at 90% setting and 100 ohm in series for 22uf cap for Fuzzpot).Then I have a pair of FF trannies with fixed resistor values...
I know thats a lot of trimmers to adjust but usually your really close to stock values if you go for (80-120hfe GE ) and 250-300 hfe Si .
This weekend I will try your method of adjusting Q2 emiter on a FF : never tried that before should be fun...
/cheers m