minor pulsing sound on second channel???

[CHATTERBOX]

My Express 5/50 was on the Burn channel at a moderate to loud volumes for some recordings and now I'm getting a constant, minor "dududududududu" sound. It's only on the second channel and very faint. Could this be tube related?
Thanks
Tony

 

[Don]

Maybe. It could also be the guitar picking something up or dirty power. Are there any other devices on the circuit that the amp's plugged into that could cause noise?

 

[CHATTERBOX]

Maybe. It could also be the guitar picking something up or dirty power. Are there any other devices on the circuit that the amp's plugged into that could cause noise?

No. Sound was still present in a different house with a different guitar. The guitar was plugged straight into the amp.

 

[Trea]

Mine has always done this but only in 50w mode and in both channels. I have no clue what causes it.

 

[AudioMonk]

Hello. This "dududu" sound, or motorboating as it's commonly referred to, is do to an imbalance in capacitance in the gain stages. It has to do with either the value of the cathode bypass cap, or decoupling cap of a particular gain stage. It often becomes apparent at higher volumes due to the increase in amplitude of the signal. I suspect, that Mesa pushed the limits in terms of having a higher value interstage decoupling cap, or cathode bypass cap, in order to increase bass response.
Try reducing the gain and bass controls when you hear this and tell me if it goes away.

 

[Trea]

It didnt make a difference in mine, but thank you for the reply.