#1
I've got my JCM 900 open from working on another problem (which has been fixed), but now I figure as long as it's open maybe I should take a stab at fixing the 60 cycle hum issue it has.

I know my building's wiring is good and properly grounded. I even tried temporarily using a three-to-two power adapter to remove the center prong, and that didn't help anything. So I assume this is something inside the amp.

It occurs on both channels, but does go away when the amp is in Stand By.

Any thoughts?

Thanks
#2
TV, Cell-phone, radio, etc.?
I'm sure I could be way off, but its worth double checking.

OH, are you running any pedals into your amp?
they could potentially be the cause.

Also, I doubt the hum is actually directly coming from the amp.
EDIT: But I could be wrong.
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Last edited by Faux~Affliction at Feb 8, 2009,
#3
Maybe a noisy preamp tube?
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#4
What kind of guitar? In my experience 60 cycle hum usually comes from single coil pickups and to a lesser degree, unshielded electronics in the guitar.
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#5
Quote by theherodies
I even tried temporarily using a three-to-two power adapter to remove the center prong, and that didn't help anything


The third prong is a ground - those 3-to-2 prong adapters aren't very safe lol
#6
The hum is there even without any guitar/pedals plugged into it, so I'm pretty sure it's something internal.

No cell phone, radio, or tv nearby - and I've experienced the same problem in every location I've tried in the last few months.

noisy preamp tube, huh? I could look into that I suppose. Would 60Hz be the correct frequency of hum I'd be hearing from something like that?

Thanks everyone for your help.
#7
Quote by theherodies
The hum is there even without any guitar/pedals plugged into it, so I'm pretty sure it's something internal.

No cell phone, radio, or tv nearby - and I've experienced the same problem in every location I've tried in the last few months.

noisy preamp tube, huh? I could look into that I suppose. Would 60Hz be the correct frequency of hum I'd be hearing from something like that?

Thanks everyone for your help.


IF it is indeed a 60 cycle hum, it's likely a dirty/noisy power, ground or polarity issue
#8
If you are from the states 60Hz is from the mains so it could be one of many things.earthing inside the amp, a broken connection, a power supply issue, microphony or shielding. Transformers delaminating etc.

Be careful, there are some nasty voltages inside anyn amp with tubes inside.