Axis Face - Can't get Q2 biased - Please Help!

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Twhjelmgren28
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Joined: 10 Apr 2017, 19:15

Post by Twhjelmgren28 »

So, I posted in the members corner that I've successfully breadboarded the Fuzz Central Axis Face. Everything worked and sounded great. I recently transferred it to Perfboard but am having issues now. Here is the schematic I'm referencing:

Image


For some reason, I can't get my Q2 to bias. When I adjust the 10k trimmer, the voltage on the collector of Q2 changes from 9.67 to 9.82 - that is literally the entire range of the trimmer. Obviously, when I breadboarded the circuit, there was a much larger range and I set it right on 4.5v...

When I test voltage throughout the circuit, I seem to be getting close to 9.84 until I get to the point where the .01uF cap meets the 3rd lug of the "level" pot. At that point, I don't have any voltage...could that be my issue. As far as I can tell, I have everything wired correctly. I've gone over it several times, double-checked that I used the proper value components, and have gone back over several solder joints (with that being said, I'm terrible at soldering but learning).

Any thoughts?
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idy
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Post by idy »

You should not get DC voltage at the volume pot: that's what that cap is for, to keep the DC "inside" the circuit.
A voltage that the bias trimmer won't change on Q2 means something is up with that transistor; loose, bad connection, ruined transistor, something. You breadboarded it and it worked, you know there's a mistake or bad solder joint.
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Twhjelmgren28
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Post by Twhjelmgren28 »

Thanks for the help. Got it figured out and you were right on. I think it was a bad solder joint. I unsoldered the trimmer then resoldered it and everything around it (including the transistor) and it worked!

Thanks again!
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Twhjelmgren28
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Post by Twhjelmgren28 »

So I did have figured out - thought I was set, went back over a few solder joints just to make sure everything was good and then I ended up back to having an unbiased trimmer. I ended up trying a different method of hooking up the trimmer (shown in a Wampler book) and that allowed me to trim it perfectly! From what I read, I basically wired it as a voltage divider rather than regulator - hopefully that is okay. So I grounded lug 3, put lug 1 to the supply at the 1k2/.033uF, and put lug 2 to the collector of Q2..

Only issue now=No output!!! There was an output yesterday when my biasing woes started - a farting noise at that point. After screwing around for a while, the farting noise left completely. I have since been working out the biasing bug. Now I have an output bug. If you have any suggestions, I'm all ears!!!

I'm going with an audio probe for now.
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