Bassman aa864 clone hum

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Bassman aa864 clone hum

Postby spoontex » 16 Nov 2017, 14:10


I've just finished my aa864 clone, Works... but... it have noise... Anybody can help me?

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Re: Bassman aa864 clone hum

Postby phatt » 18 Nov 2017, 07:05

I have not heard that noise from those amp designs,,, hum?? check all the filter caps are connected especially the Screen supply.
Does the amp make clean audio with guitar plugged in?
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Re: Bassman aa864 clone hum

Postby DrNomis » 01 Dec 2017, 08:34

If you're using Carbon Composition resistors in your Bassman build then that's most likely what's causing the noise since Carbon Composition resistors tend to be inherently noisy, it could also be a cold solder-joint that's causing the noise too.

Might even be one of the preamp valves that might have gone noisy, try temporarily swapping out the first preamp valve (V1) for another known good one to see if that fixes the noise issue, if not, then try doing the same to the other two preamp valves.

A slightly loose valve socket contact can also cause noise issues too.
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Re: Bassman aa864 clone hum

Postby Aharon » 02 Dec 2017, 02:52

That sounds like ground noise ,also check that the heaters are wired correctly and that you didn't swap pins ,meaning all 4/5 go together and all 9 go together ,don't cross wire them or the humbucking effect is gone.Same with the power tubes .Also if you don't have a heater ground create an artificial one with two 100ohm resistors to ground.recheck all grounds ,use star grounding.Also check the vol pot wiring,does the hum go up with the vol?
Check the input jack ground,is it isolated?,Finally read Geofex troubleshooting for tube amps or Paul Ruby's page .
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Re: Bassman aa864 clone hum

Postby lead2203 » 02 Dec 2017, 04:57

It's the grounding. Separate the power section from the pre. First filter and second to their own grounding point with associated ground wires. Phase inverter and preamp to their own grounding point. Grounding everything to one point doesn't always work. Doing it that way it picks up noise from the current of the power transformer center taps and first filters grounds. Separate those and it stops the noise from going up stream into the preamp.
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