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System Hum Question

Hi, all. I'm trying to figure out a vexing system hum issue and came across something fairly perplexing. When I disconnect the inputs from my amplifier (but leave them connected to the preamp), the hum goes away. However, when I disconnect the inputs from the preamplifier (and leave the other end connected to the amplifier), the noise in my speakers gets louder. Why is this?

(I've tried cheater plugs, a Humbuster, plugging amp + preamp into the same outlet, and unplugging everything else in my apartment. I don't have cable, fluorescent lights, or dimmers. The hum comes and goes with no discernible pattern. I live in a large apartment building.)

Thanks for any guidance you may be able to provide.
bongeiste
ddd1
261 posts
 
Have you tried swapping out the interconnects for some with better shielding?

Checked you electrical outlets for proper grounding?

Tried swapping out your preamp/power amp power cords?

Try hooking up a CD player direct to power amp and check for hum?
zmanastronomy's avatar
zmanastronomy
738 posts
 
Also try a grounding wire from the pre to the amp.
I've also heard that just changing IC's makes these hums go away. Shielded or not.
bongeiste OP
2 posts
 
I'll have to try those suggestions. As I don't have any good A/V stores around, I'll probably go online to get some new interconnects. I don't have a CD player yet (been using my computer via optical cable), so I won't be able to test that suggestion anytime soon. Is there any reason why this hum would be there some days and not be there other days?
jea48
4,425 posts
 
However, when I disconnect the inputs from the preamplifier (and leave the other end connected to the amplifier), the noise in my speakers gets louder. Why is this?
No doubt.... Don't do that. Having the ICs connected to the amp but not connected to any thing on the other end works like an antenna and will introduce large amounts of RFI and EMI to the input stages of the amp.

Not good on the speakers either.
etbaby
138 posts
 
Hi Bongeiste,

I just had this problem. One of your source devices (CD player, turntable, or tuner) has a 60 cycle hum on its audio outputs. Disconnect one source component at a time until the hum disappears. Then take the source component in for repair.
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