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Hello All, Just got a used (mint) Creepy Fingers Magnabender MKI and I'm trying to figure out the bias switch. In the up position it works great, just like a MKI tone bender should. With the bias switch in the down position the pedal starts to oscillate and make unusable sounds. The only way I can get it to sound ok is to turn the attack all the way down until the clipping, oscillating stops. Any idea what's up with the circuit? I wonder what his intention was for this switch?? here are some photos of the circuit:

resistor color codes

I think thats 46k or 47k. not sure if thats blue or purple. in the up position it connects those two wires together on the back of the switch. when it n the down position it adds the resistor. its probably just starving one of the collectors. 47k might be a lot but it all works out on a 3 transistor fuzz as long as the transistors have enough gain. darlingtons have 100k collector resistors and thats normal. but the gain is over 1000

oh and the answer to your question is to just solder in another resistor in parallel with the 46k thats on there. you want 10k total. this will make it less wild. using a parallel resistance calculator

12777.77777777777 = 12.7K
anything in the 10k to 15k should work. a 10k gets you 8.2k total. dont remove the resistor thats on the switch. just order a resistor from tayda for $1 shipped.

AFAIK, the bias switch is to compensate for when it gets really hot and the trannies start to crap out.
You could always just email Brad and ask him though.

eatyourguitar wrote:oh and the answer to your question is to just solder in another resistor in parallel with the 46k thats on there. you want 10k total. this will make it less wild. using a parallel resistance calculator

12777.77777777777 = 12.7K
anything in the 10k to 15k should work. a 10k gets you 8.2k total. dont remove the resistor thats on the switch. just order a resistor from tayda for $1 shipped.

Thanks. If I was to replace the bias switch with a pot, what value pot should I use and how should I wire it??

Just talk to Brad. He's plenty nice.

A 50k pot will do it. If you want less range you can use a 25k. There are also tricks to make a 46k pot.

thanks. Brad just emailed me and said that he would be glad to put a pot in it.