18megs to bias a Fuzz Face?

[spaceace76]

I finally got around to fixing up my GGG silicon fuzz. Since the 100k pot I'm using for biasing isn't the best method, I thought I could just measure the resistance when it sounded the best and swap it out for a resistor instead. So I check the voltage and make sure it sounds good, then check the resistance, and my meter says 18megs!!!

Am I reading that right? I didn't bother to match the transistors, but 18 megs seems completely outrageous. Did I do something wrong? One lead on each of the outer lugs of the pot, right? How can a 100k give me an 18m reading? I even removed the pot and checked it to be sure it hadn't magically gained 17.9 megs of resistance without my knowledge, and it's fine. I'm not sure I even have the right value resistors to double check, unless I put 4/5 of them in series.

So what the hell? Am I having an off day or is 18m a reasonable number in some cases?

[Solidhex]

Yo

  Maybe check your multimeter's battery? haha. What resistor are you using a 100k for? If its the usual 8k2 that's way too big.

--Brad

[spaceace76]

I took out the 8k2, tried a 25k pot and only got unity gain with very mild fuzz, the 100k is the only thing I've tried so far that can get the collector to 4.5 volts, or even close to it. It sounds great when dialed in properly. Maybe I should get a hold of a 50k and see if it works better. I think a smoother taper would help a lot too. This one puts most the the control right at the end, kinda ruining the idea of a pot to begin with.

But would this board even carry 18megs of resistance? The values just don't seem high enough for it to end up at 18M. Maybe I have to measure the resistance of the pot after removing it? Not to check if it's working, like I did before, but to single it's value out. I suppose it's worth a shot.

[JOHNO]

I finally got around to fixing up my GGG silicon fuzz. Since the 100k pot I'm using for biasing isn't the best method, I thought I could just measure the resistance when it sounded the best and swap it out for a resistor instead. So I check the voltage and make sure it sounds good, then check the resistance, and my meter says 18megs!!!

Am I reading that right? I didn't bother to match the transistors, but 18 megs seems completely outrageous. Did I do something wrong? One lead on each of the outer lugs of the pot, right? How can a 100k give me an 18m reading? I even removed the pot and checked it to be sure it hadn't magically gained 17.9 megs of resistance without my knowledge, and it's fine. I'm not sure I even have the right value resistors to double check, unless I put 4/5 of them in series.

So what the hell? Am I having an off day or is 18m a reasonable number in some cases?

When you use a pot as a resistor you have one lead on the outer lug and one on the middle lug. You say you measured the pot on the outer lugs. All that does is measure the total resistance of the pot. If you connect it in circuit like that,ie the two out lugs, all that will do is give you the total pot resistance,ie 100k. If i was you i would be checking all the resistor values in the circuit. Make sure the 330 ohm is 330ohm and not 330k. All that i think is needed to bias this circuit is say a 4k7 and a 10k pot connected in series where the 8k2 is supposed to go. Twiddle the pot till you get your 4.5v at the collector and then remove the pot and check the value. Say the pot reads 7k1 for instance, you then add 4k7 to that and you get 11k8. So just stick in a 12k resistor. Good luck with ,JOHNO

P.S I dont know how in hell you get 18m from a 100k pot. Check some resistors that you know the value of with your meter and see what is says.

PPS Nice photo, Ace rules.