by bordonbert Sat Apr 09, 2016 1:34 pm
What level have you got your Gain, Volume, Master Volume, Boost and Power Soak set at LP? I have known people to complain it hums with all of those controls set at max! Does it hum the same when you take it to a different location like a rehearsal room? Some rooms are just plain more noisy. Fluorescent lighting, TVs, computers are all very bad at chucking out EM gunk that your amp can pick up, and even your mains supply can be a problem if you are on the same line as say nearby commercial workshops. It used to be a big issue for hifi which is much more demanding than guitar work in this respect. Sometimes it was necessary to get the supply people to switch your house onto a different phase of the local supply to get away from nasty spiky interference brought in on the mains itself. That spawned a fad for expensive "mains regenerators" which converted the mains to a DC supply and used that to generate an ultra clean 240V 50Hz signal at high currents to feed to the hifi equipment as mains. No, no, no, no! It isn't a necessary thing for guitar!!!!!
Valve amps will always have highish levels of hum in them, it's the nature of their power supplies which are ultra primitive. SS amps have regulated supplies at key points which dramatically cleans them up. Because of the very high voltages involved that is much more difficult and costly for valve stages. And even if you made the amp quieter with regulated supplies you would have taken away another tonal "good thing", power line sag. The regulation means that the supply is "stiffer", i.e. it stays at its correct voltage even when higher currents are demanded.
Unless you are hearing it intrusively when you play I would say it's probably normal. With a band around you, is it audible when they play but you are in a silent phase building up to that crashing solo? The GM36 should not be significantly noisier than most other valve amps and it's quieter than many.