Question about my new GK MB210

[Bradd Douglass]

I am getting a very annoying high frequency hum from my amp while playing. Everything is set as initially recommended by GK. EQ and boost at 12, Master at 3, Contour and Horn off, and Limiter on. The sound is not affected by the Gain knob, but it is affected by the Master knob. With the Gain off the sound can be cut by cranking the Master down. Is this normal?

 

[Jeff Scott]

Hum? Hiss, more likely. Does it get worse when you turn the horn on?

 

[Bradd Douglass]

I can't bear to turn the horn on.

 

[Jeff Scott]

That does not sound normal. I played through a MB115 today and it was quiet. If you just bought this new, either return or exchange it.