Noisey Hum on Marshall MG15DFX

[Stratlingun]

Hi, I just got a used Marshall MG15DFX that has a pretty loud hum when you jack in the cord and turn up volume( noise is proportionate with volume ), mostly in "overdrive". In "OD" the noise is a more grainy "annnnnh" type of sound. Not as bad in "Clean", but it hums also. Does not matter if guitar is plugged to other end of cord or not, noise is the same either way. If I unplug the cord( and I have tried other cords ), amp is quiet with all controls max. All amp functions and FX seem to work properly. I just went by Guitar Center and tried similar amps, with a cord plugged in and they were very quiet in comparison. What to do???

[Enzo]

Probably broken ground connection at the input jack. Pull the board and see if any of the jack pins have cracks in the solder.

[Stratlingun]

Thank You. I will check for that.

[Stratlingun]

I soldered what looked like a bad joint, and that stopped the scratchiness of the hum. now have smooth hum. since you mentioned broken ground I decided to check the outlets in this VERY OLD home I am renting. I got 123v N-H, 82v G-H, 34v G-N. Actually I got different readings in various parts of the house. I'm no electrician, but I'm pretty sure this should not be. So I think this might be the source of my hum. If it is, is there a way around this? I think I read about some kind of power strip or UPS that supplies its own ground or filters a bad groud? Do you know of anything like this?

[Enzo]

Well, that ought to be corrected, but I am sitting here, spending your money there.

A ground connects to the earth ultimately. if the wiring doesn;t go there, it is dificult for some device to make such a connection from thin air.

But don;t guess or assume, take your amp somewher else and plug it in. To a friend's house, to work with you, hell, anywhere it can be plugged in, if the rest area on the freeway has an electrical outlet, try it there. That ought to get some looks. If the amp sounds OK everywhere else, then I would indeed blame your house wiring. But if it still hums there, then the amp still has issues.

[Jazz P Bass]

[QUOTE=Stratlingun;235500]I got 123v N-H, 82v G-H, 34v G-N. QUOTE]
The "Ground" wire of a properly wired outlet is the exact same potential as the "Neutral" wire.
At the mains enclosure they are connected to the same rail.
It sounds to me like the third leg is not even present.
It is a three wire outlet with two wires hooked up.

[Stratlingun]

Yep, thats the way I see it. I'm in an old rental house . I think the owner put in 3 prong outlets to appear like he's in code, but never bothered to wire them up. Today I noticed an unused ( earth anchored )tv antena pole 1 foot from one of my living room windows, so I will run some wire from it to an adapter and see how that works.

[Jazz P Bass]

I would not bother.
The missing "ground" on the outlet is not "causing" hum in the amp.
Read what I posted.
The "Ground" & "Neutral" are the same.
The "Ground" wire is for safety, not dehumming.

[Stratlingun]

Well I just tried another small amp in my house, old Kustom, which I would have expected to be even louder, but it was much quieter. So I guess definitely an amp problem. Any ideas, it would be a nice amp if it was not for the hum? Don't know if it helps but when in overdrive while turning up the gain at about 7 on the dial the intensity of the hum immediately doubles or more, like flipping a switch. Oh and I did try the antena pole, it noticably gets a little smoother, but still loud hum.
Thanks for any help.