Proper Way To Externally Bias A Fuzzface

[Easywider]

Building A Fuzzface On An Eyelet Board , Want To Externally Bias With A 10k Pot .Left The 8.2k Resistor Off The Board & Ran Wires Where The Resistor Would Go . Whats The Right Way To Do This....Do I Just Connect The Wires To Lugs 2 & 3 Of The Pot ? Does It Matter Which Wire Goes Where ? Thought I Read Somewhere That One Of The Lugs From The Pot Goes To The 470ohm Resistor ? Any  Help Greatly Appreciated !

[nico13]

I've seen some schematic with a 10K bias pot connected to a 1K resistor (replacing the 470R).

I don't think the way the pot is oriented being very important. You can connect lug 1 of the pot to the resistor and wire lug 2 to lug 3 together to the transistor's collector.

[Easywider]

Nico , Thanks ! Since I Left Out The 8.2k Resistor & Replaced With Wires , Couldn't I Just Put The Wires On Lugs 2 & 3 Of The Pot , Since The 8.2k Resistor Goes To Q 2's Collector . Also , Why Would I Need To Tie In With The Output Resistor For Lug 1 ?

Thanks ,

Chris

[Solidhex]

Yo

  I just connect the 3rd lug to the collector, 2nd lug to the junction of the 470r and output cap. You can bridge the 1st and 2nd lugs together if you want but it won't sound any different.

--Brad

[analogmike]

proper procedure when using a pot as a variable resistor is to tie the unused lug to the wiper. Like adding STP to your oil (does anyone use that anymore?).  Have fun and good luck!

[flo]

Or an "automatic bias" circuit (which I have not tried yet...):

From http://www.hollis.co.uk/john/circuits.html

I've taken the classic Fuzz Face circuit and added optical temperature compensation. This ensures that the output stage is biased at half the supply voltage regardless of variations in the transistors, particularly those caused by temperature. Tweaks: Obviously, one could make the bias point adjustable, but it sounds fine set to halfway. One could add a resistor across the LDR to set the maximum value which would also cut current consumption slightly as the LED would go darker in response. This achieves lower minimum values too. Try 47K.