Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: isaac_teller on June 13, 2019, 05:13:43 am
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Hello. I built a 5E3 style circuit with 6JB5's in the output, 6SL7 and 6SZ7. It is very quiet except for a buzz that starts at about 4 on the volume, increases to max at about 5-6 and goes away at 7. What could cause this? The signal leads are shielded and the pot bodies are grounded. Other than that it sounds great. Thank you.
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Maybe the pot itself? Try taking a few measurements in the sweep, and a spray of pot cleaner/isopropanol just in case?
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Sounds like a ground (internal ground loop) problem... Could you give any information on layout (especially ground scheme)? Is the hum still within acceptable limits or is it just too loud?
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> a buzz that starts at about 4 on the volume, increases to max at about 5-6 and goes away at 7
The lead from the wiper to the next stage is picking up buzz from "somewhere". When full-down or full-up the buzz is shorted-out; at mid-way (not near either end) the buzz is maximum.
Shielding normally makes this insignificant. Re-examine that shielding. The shield should return to the ground of the stage it is going to, normally directly TO the stage's cathode RC network ground.