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In Reply to: re: still trying to track down a hum... posted by mr9iron on September 15, 2012 at 10:11:35
Chris, Tre,
bummer, I tried the set up exactly as you guys described with new high quality coax cable, still same exact result, no change.. I ran a solid 12 gauge wire connecting the grounds of the RCA plugs and then from the center of that wire to the signal ground, no change, still hums. I also tried grounding them separately, and not at all, still all the same result..
could the loop be coming from somewhere on the board? It seems like I have exhausted everything on the RCA end...
thanks for your suggestions, much appreciated..
Jeff
Follow Ups:
"I also tried grounding them separately, and not at all, still all the same result."
The "not at all" indicates that the RCA connectors are grounded somehow. They must be touching the chassis.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Tre,
yes, I was expecting the same result... but with both grounds off the RCA's, the amp is the same.. the real bad hum which you mentioned, will only occur if I disconnect the other end of the coax... and I have to disconnect it on both coax cables for it to do the big hum.. I know that sounds outrageous, but I kid you not, this is what is happening. I tried grounding the other end of the coax to other points on both sides, but no difference..
It sounds insane, I know, but that end of the coax is suspicious that it behaves like this. The path to the 12by is pretty simple and I can't see any other place it can ground.. I do think there is something up with the other end and not the end of the RCA's
It was suggested that I check DC voltage from all the grounds to chassis and the RCA grounds and the filter supply grounds all drop to "0" DC volts.. when I checked last night.
again I seriously thank you for your replies on my thread, I am losing all hope on this lately..
J
Take a pair of RCA interconnect cables and cut one end off of each.Solder the wire end to the circuit at the 12by7. Positive to the grid stop resistor (10K), top of the 1meg resistor, and ground (shield) to the same ground point of the grid resistor (1meg).
Do both channels. Disconnect the in-chassis input cable.
Connect the other ends to your preamp. Make sure nothing is grounded. If any of your equipment has 3 prong plugs, use a cheater adapter so nothing is earth grounded.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 09/19/12 09/19/12 09/25/12
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