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Old 8th September 2012, 04:34 PM   #61
willamp is offline willamp  United States
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If you disconnect one channel does the hum go away? If so it
could be multiple paths to ground causing current flow through the interconnect shields. This can then induce hum in the signal paths. I just went though this with a power amp build. Solution was to attach the signal grounds from both channels to the same point in the grounding scheme such that there would be no current flowing between them. For me the problem was in the power amp chassis but didn't show up until both channels were connected to my passive pre which then ties the two shield grounds together. I would think you could get the same scenario in the pre-amp chassis. I suppose it could still be a similar problem even if it occurs with only one channel connected. Idea is to make sure signal shield has nice quiet path to ground where there is no current flowing.

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Old 9th September 2012, 12:07 PM   #62
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Sorry Guys, I was unexpectedly whisked off to Saturday afternoon football - Michigan State vs. Central Michigan at Mt. Pleasant, Mi. (My school, CMU lost the game but both bands were a real treat. As DM, I started a post-game "circle around the tree - single file" ceremony that continues almost fifty years later.)

The configuration has no common mains wiring. That's what makes the problem so confusing. The fact that the JC-2 is completely free of hum when connected to the powered speakers indicates the problem has to do with the pre to FE combination. I'll do some more puttering today.
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Old 9th September 2012, 01:13 PM   #63
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I replaced the JC-2 with a Carver C-1 and the hum remains. Commercial shielded pre-made interconnects were used. Again, a direct connection from the Mini 2496 DAC is perfectly clean. Has anyone successfully used a pre of any kind with the FE?
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Old 9th September 2012, 01:19 PM   #64
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Quote:
Originally Posted by bcmbob View Post
Has anyone successfully used a pre of any kind with the FE?
Sure, the DCB1 and the pre-outs of my Marantz receiver. No hum.
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Old 9th September 2012, 01:27 PM   #65
bcmbob is offline bcmbob  United States
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O.K. Do you see anything here that could be causing the problem?
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Old 9th September 2012, 01:28 PM   #66
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Bob,

If you haven't read it yet, check out the link in the Fremen - Beta build thread, post #1105. In that paper, there is a procedure for diagnosing hum in a single ended connection. I found it helpful.

Jac

Last edited by lehmanhill; 9th September 2012 at 01:31 PM.
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Old 9th September 2012, 01:34 PM   #67
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Thanks Jac, I'll read it now - as this is the first time I've had any hum problems other than an open input. I'm off to study hall
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Old 9th September 2012, 01:38 PM   #68
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O.K. Do you see anything here that could be causing the problem?
No, it seems identical to mine... regarding grounding and connections.
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Old 9th September 2012, 01:49 PM   #69
willamp is offline willamp  United States
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Bob, if you only connect one channel of amp to pre-amp is there a hum?
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Old 9th September 2012, 01:53 PM   #70
bcmbob is offline bcmbob  United States
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Yes, each single channel actually increases the noise on both channels. It is really more than hum, and I will post a recording if it on Boxnet later this morning.
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