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Sunn Musical Equipment => Q & A => Topic started by: porcupine on July 14, 2018, 04:30:33 pm

Title: Beta Lead - loud hum with no signal
Post by: porcupine on July 14, 2018, 04:30:33 pm

I recapped my Beta Lead and am now having some problems with it. After putting it back together I plugged into channel A. It sounded great for a few seconds and then there was a loud thump/pop sound. The channel LED went out and the amp stopped passing guitar signal, now just putting out a loud hum (which can't be controlled by any of the knobs). I shut the amp off immediately and opened it back up. Everything looked ok, nothing burnt and the fuses weren't blown, so I tried again.

Channel A worked great, and I played through it for a few minutes with no problem. Channel B worked but had a lot less gain at the exact same EQ/drive settings. I plugged into the Both input and I got the loud pop/hum again, no LEDs lighting up, and no guitar signal passing. Went back to the individual channels and I'm getting the same result. Any clues what could be wrong?

Title: Re: Beta Lead - loud hum with no signal
Post by: loudthud on July 14, 2018, 09:22:11 pm

There is a -15V source on the power amp board. Make sure it is steady and has good connections to the preamp board. The channel LEDs run off of the -15V supply.