2. amps-preamps
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Help with hum

I have a hum coming through both speakers. It is independent of volume control and completely stops when the preamp is disconnected. Disconnecting source from preamp has no effect. I have tried switching cables and tubes from channel to channel but it keeps humming. I have tried all combinations of cheater plugs on both amps and on the preamp but with no improvement. Any advice regarding cause or diagnosis is appreciated. Preamp is Cary SLP-98 and amps are Manley Neoclassic 300b's.

Thanks in advance,

Dave
128x128dbrewer12345
dbrewer12345's avatar
dbrewer12345 OP
16 posts
 
Zman,

I tried your tip without success. I did eliminate the hum when I touched a wire grounded to the pre to the (+) speaker terminal of either amp. I realize that is not a realistic solution but may help someone offering advice.
zmanastronomy's avatar
zmanastronomy
738 posts
 
Try hooking the ground wire from the source to the amp.
tarsando
578 posts
 
Since there is a ground connection on the interconnects, I don't see how connecting a separate wire as suggested would help. Plus I personally wouldn't do it because of possible electrical consequences that I don't really understand. Better safe than sorry. Good luck finding a solution!
jea48
4,423 posts
 
It is independent of volume control and completely stops when the preamp is disconnected.
Just a guess but I would bet the ground loop is caused by one of the amps. When you have both amps connected to the preamp the ground loop circuit is completed by the ics.....
Just for a test try hooking up only one amp at a time to the preamp. Check for hum.

Jensen makes an isolator that can be installed between the preamp and the amps.

http://www.jensen-transformers.com/

http://www.jensen-transformers.com/an/an004.pdf

markwatkiss
508 posts
 
Been there.Save yourself some grief and borrow or steal another pre amp,plug it in the system and if the hum disappears you will have identified or eliminated the pre amp as the source.
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