Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Captain chunkulus on January 27, 2019, 09:27:01 am
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Okay, so I've looked all over the Internet and have found very few posts anywhere about this problem. I have a preamp that I built that the gain pots won't kill all the volume. They are grounded well. I have read that it might be capacitive Coupling? But I haven't been able to find any real solution. The preamp is a high gain marshall type circuit with 3 stages and a directly coupled stage for a total of 5 stages. Has anyone ever had this problem? Is there an easy fix? The preamp doesn't hum, buzz, sounds and plays right on but the gain pots just won't zero out. They are brand new alpha pots. Any thoughts? Thanksort.
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You probably have this correct but gonna mention it anyway. Whatever leg of that pot you want grounded out (CCW, or CW) needs a ground connection unless by grounding out you mean that the wiper becomes disconnected from the either of the end terminals at full rotation (CCW or CW), which in that case you may have a No-Load pot vs a standard pot.
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You should always post a schematic. Signal can couple to a later gain stage through the B+ rail. E.g.'s: more than one gain stage shares a B+ filter node; bad ground in the B+ rail; stages shares a combined plate resistance. Also, signal ground loop, which is grounding/layout issue.