GK MB150S buzz

[alvinliaobass]

I recently bought a used GK MB150S amp. And I found out after playing for a while (20-30min-ish), the amp starts buzzing even when every knob turned all the way down, bass unplugged, and the internal speaker disabled. The amp is plugged straight into the wall outlet, no extension cord used.

Anyone knows what the issue might be? Should I talk to the last owner about this?

 

[agedhorse]

Try it on a different power source, the amp was designed before there was a large number of non-linear loads on portions of the power grid.

This generated noise on the power line which can cause magnetostriction in the core of a power transformer that uses a laminated core. This is a mechanical noise rather than an electrical noise.

This is a very common symptom when the amp is operated from an inverter that generates a modified sine wave due to the discontinuities combined with high rise time waveforms.

New designs are more resistant to this effect, which can become worse with an increase (and sometimes a decrease) in temperature. The laminations are VPI treated, are mechanically clamped or both.

If the noise goes away in a different location, it’s likely the cause. A truly qualified tech will be able to confirm this. An under-qualified tech will not grasp the concept.

Generally it’s more annoying than an actual problem.

 

[alvinliaobass]

Try it on a different power source, the amp was designed before there was a large number of non-linear loads on portions of the power grid.

This generated noise on the power line which can cause magnetostriction in the core of a power transformer that uses a laminated core. This is a mechanical noise rather than an electrical noise.

This is a very common symptom when the amp is operated from an inverter that generates a modified sine wave due to the discontinuities combined with high rise time waveforms.

New designs are more resistant to this effect, which can become worse with an increase (and sometimes a decrease) in temperature. The laminations are VPI treated, are mechanically clamped or both.

If the noise goes away in a different location, it’s likely the cause. A truly qualified tech will be able to confirm this. An under-qualified tech will not grasp the concept.

Generally it’s more annoying than an actual problem.

If that is the confirmed problem, will there be a fix to this if I want to take this on gigs? Thank you very much.

 

[agedhorse]

If that is the confirmed problem, will there be a fix to this if I want to take this on gigs? Thank you very much.

The fix (IF this is the cause) is to either play in locations that don’t have the noise (which is why I suggested trying it in a different location) or replace the power transformer with the correct part (the part is unlikely to still be available since the amp has been discontinued for some time).

There may be other options that a qualified tech can try, but they are unlikely to solve the problem.