Hum on Crown sub-bass issue

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08-17-2009, 10:40 AM
robertbartsch

Hum on Crown sub-bass issue
I'm running three Crown 802s in stereo mode and one of these is feeding a single sub bass channel into a JBL 2245 and it has developed a hum that I'm having trouble eliminating. The other non-sub bass channels (e.g., the other two Crown driven amps/channels) are OK without any hum.
- The sub-bass channel is being fead by a Adcom preamp and I'm using a commercial adaptor (3 pin XLR to 2 point RCA) between the two components
- Each amp is grounded using (i) a three pin grounded 120 Volt power cord running into a grounded fuse protected multi-extension cord, and (ii) separate ground wires from each amp's frame to a cold water pipe in the basement.
- The pre amp and CD player are not grounded directly to the water pipe but are grounded using only the 3 pin 120 volt extension cord. The music signals are sent between these two units using standard home RCA-type cable.
I assume there is some type of ground loop issue causing the hum but I'm not sure where to start.

Questions:

1. Is the double grounding to the water pipe for the three Crown's an issue?
2. Should all or none of the electrical unit frames be grounded togeather?
3. Is the commerical XLR to RCA cable adaptor an issue?
4. Is there another source that could be causing the hum?

Thx...
08-17-2009, 11:34 AM
robertbartsch

Yeh, I read the other post on ground loop issues.

I suppose I will try a few things that are suggested there first.
08-17-2009, 04:15 PM
JBL 4645

Have you switched leads around to isolate the issue as it might be break in the cable?

Also try attaching some wire from amp to the other that may or may not solve the elusive humming Gremlin.

.
I had a bitching humming/buzzing issue a few years ago:banghead: that took 24 hours, I stayed up all night long! It turned out the issue was the old SONY TV that I used to have that I recently installed at the time.

I discounted the Earth lead to the TV and the humming/buzzing disappeared like magic.
08-20-2009, 09:05 AM
robertbartsch

...this issue appears to have been casued by a bad RCA cable.

Thx..
08-22-2009, 07:36 PM
boputnam

Quote:

Originally Posted by robertbartsch

...this issue appears to have been casued by a bad RCA cable.

True, or is it merely any RCA interconnect in that position? Anotherwords, the culprit might not be the cable, but it might be the involved component...