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DIY Stompboxes => Building your own stompbox => Topic started by: Yun on February 26, 2004, 04:01:10 PM

Title: Mis-biasing problem, how do i fix it?
Post by: Yun on February 26, 2004, 04:01:10 PM
Okay; i built a Fuzz Face (for the millionth time) and as usual i get that so not loved but all too familiar Blatted, gatey sound.  i know Q2 is mis-Biased.  i went to the FAQ and found that out.  i clicked on the link; and it tells you everything else you want to know BUT how to fix the thing.  

So my question is:  How do you fix or Bias a mis-Biassed transistor eh?

Thanks...
Title: Mis-biasing problem, how do i fix it?
Post by: Marcos - Munky on February 26, 2004, 04:25:40 PM
I think you do this changing the value of the resistor that goes to the collector of the transistor.
Title: Mis-biasing problem, how do i fix it?
Post by: smoguzbenjamin on February 26, 2004, 05:51:47 PM
Yun, post your transistor voltages, that way you can tell a lot more from them, and you'll know what to do. So will we for that matter :)
Title: Socket...
Post by: petemoore on February 27, 2004, 03:22:26 AM
Or better yet trimpot that thing.
 I gotta buncha them FF round here with trims on Q2C.
 Just look at a Runoff groove schematic for say multi-face..and put something like that on there.
 I use a 25kpot , or 10kpot, or 10kpot with a 4k7 resistor off one end...that way I have range of anything between 4k7 and 14k7 resistance there...pot is easy to dial in that way.
 If you have no pot you can use a socket and insert different fixed R values in it.
 If you don't have a socket, you can put something like 18k in the board with enough leg shown on top of the board to strap a parallel resistor of your choice [this way is labor intensive, see above methods] across it thereby lowering the resistance to an amount that causes Q2's collector to settle at around just above half supply voltage or 4.5v-5.5v, using a battery thats about 9v.
Title: Mis-biasing problem, how do i fix it?
Post by: Yun on February 27, 2004, 03:43:04 PM
Thanks for the ideas, guys.  As for the voltage reading: can't do it, man.  My Overly curious Nephews blew my MM up  :oops: .