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Old 16th September 2002, 08:52 PM   #1
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Question What could be wrong if running a ground

wire from ANY of my sources to my brand new-just finished -(finally) Leach amp causes a very nasty (60Hz?) hum to vanish completly? ( Amp is dead silent before introducing an input from a source) I first tried lifting the third conductor from the wall plug as per the Leach site, no change. Then I tried using just one of the source's RCA inputs, hum volume decreased at least by half- but still there. I tried inverting the wall plug for the source AC power- no change. Then I added a temporary jumper wire from the source chassis to amp chassis--complete and utter silence even at full gain. Perfect fix. Plays fine- all day long- no problem. OK, I can live with that, but what the heck could be going on that adding this jumper wire is the apparent cure?
I know, another ground loop nightmare!
Thanks for your thoughts and help.
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Old 16th September 2002, 11:04 PM   #2
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It sounds like your amplifier does not have a solid chassis ground connected to the "star" Grounding point. Make sure that all your grounds including: two speaker returns, power supply common, signal return, power return, and earth are all connected to a single point on the conductive chassis. Also check to make sure that the signal lines are not touching the chassis. Remember that there are two grounds per board/channel in this amplifier. Also, are you using a true earthed outlet?

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Old 16th September 2002, 11:05 PM   #3
skaara is offline skaara  Slovenia
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ou must ground signal gnd to wall gnd somewhere. You might didnt do it in your amp..
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Old 17th September 2002, 09:18 AM   #4
djk is offline djk
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http://users.ece.gatech.edu/~mleach/...aphics/ckt.pdf

Check R51, it may not be there, it may be the wrong value, it may be open. You probably have a ground loop.
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