All dials at 10 get loud roaring hum

[machinegun1]

Hi guys,

I own a VM combo - has anyone else had/have this this problem:

HDR mode on, Mid boost on, - Turn all dials up to 10 except detail and body knob. No guitar cord plugged in, nothing in the return loop. As I turn up the detail and body knob the hum gets super loud. ( the hum is o.k when the body an detail are at zero)

Setting the master volume lower or switching to LDR mode the hum/white noise is a lot less. I'm guessing it's possibly a preamp valve or power valve but would just like to know if anyone has had this problem?

Sorry for all the negative posts (I am enjoying the sound of the amp!!).

[machinegun1]

I've edited what I wrote above as I had more time today trying to find the source of the hum e.g resitting valves, checking bias etc) (bias was 43mV on both so I pushed it up to 45mV). Checked the earth continuity. Also no problem with excessive hum if body and detail are zero and I plug guitar into efx return loop (so don't think it is power valve even though 1 has a acoustic rattle that doesn't come through the speakers). Tried a different preamp valve in v2 but got the same result as what is written above. Tried swapping v1 and v2 and got feedback when turned detail up

[rasze]

i also get a pretty loud hum when i have the master over 3! hope its the tubes because i still have warranty on them.

[machinegun1]

Hi rasze,

Do you get the hum with no guitar plugged in? The hum I'm experiencing you would have to speak loudly, if not shout to be heard over the top of the hum. And the fact it can also self oscillate (no guitar plugged in) with master over 8 makes me think it is not normal even for a high power high gain amp.

[rasze]

i havent tried without the guitar yet, but i didnt experience the loud hum with my previous amp with the same guitar and fx.

[machinegun1]

Hey guys - I found the solution to my problem!!!

Normally when the input jack has no guitar lead plugged in to the input jack - the input should get 'switched' to ground via sprung metal in the jack ( At least I think so anyway!).

Because my amp is 5 years old the sprung metal which should do this no longer springs back to 'short' the signal wire to ground - so the input signal to the valve is an 'open circuit' and acting like a aerial picking up 50hz hum. With everything set to high gain - the hum was heavily amplified hence the loud roaring hum

Hope this helps anyone else out there with this problem

kia-ora