Can I ground my preamp?

Clio09: I've been told that if one uses interconnects that are shielded, it's best that the shield is connected to the ground at one end of the cable. I've also been told you can disconnect the entire ground at one end of an interconnect. Never tried it, but maybe someone here can comment on that.

Tvad: Correct. The end that connects to the preamp should have the shield connected. The end of the IC that installs at the amp(s) or sources has the shield unconnected. This also goes to the issue of directional indicators on some interconnects, which will point to the end that has the shield connected (rather than indicating signal flow).

That is correct, but only in the case of interconnects that do not use the shield as the signal return conductor. Or interconnects that have an inner shield used as the return conductor, and a separate outer shield, which may be grounded at only one end. It is common, especially among lower priced interconnects, for there to be one shield, and for it to be used as the signal return conductor, in which case disconnecting it at either end would result in very loud hum.

Also, based on what I've read different manufacturers do not always define the arrow consistently, in some cases having it point to the end at which the shield is grounded, and in other cases having it point in the direction of the destination component.

Best regards,
-- Al

Rrog, disconnect the interconnects from your amp and turn it on. If there is still hum, you have a problem in the amp. This is unlikely. If not put the ic between the preamp into the amp, but with nothing plugged into the preamp. If you have hum, it is the preamp. If it is in one channel, that is the problem. This is improbable. Switch the ics at the preamp. If it switches, it is the preamp.

If no hum, connect one source. The one that adds hum is the problem. Put a cheater on its pc. If that doesn't help it, it is in that source.

Also, based on what I've read different manufacturers do not always define the arrow consistently, in some cases having it point to the end at which the shield is grounded, and in other cases having it point in the direction of the destination component.

Best regards,
-- Al
Almarg (System | Answers | This Thread)

Didn't I state this in my post? I certainly intended to.

I need to start writing more clearly and completely...leaving no comment less than fully developed.

Bojack,

Does each amp have its own dedicated circuit?
If so are both dedicated circuits fed from the same Line, leg, in the electrical panel?

Did you try using ground cheater plugs on the amps? Did the hum stop? For a test I would try that first.

Did you check each amp for the proper AC polarity orintation?

Just curious what happens if you disconnect all input sources from the preamp. Unplug the preamp from the power outlet. So all you have is dead preamp with the two amps connected to the preamp by the ics. Is there a hum?
(If the preamp has auto mute on power shut down this test may not be valid.)

Just a point of info:
I doubt that the small wire in an IC will carry the high fault current, in the event of a ground fault condition, long enough to safely trip the branch circuit breaker open.... Good chance it Ain't gonna happen.... In the case of a single pole 20 amp breaker as much as 150 amps, or more, of fault current could pass through the breaker before it would trip open. The instantaneous short circuit current flow could be in the thousands of amps. It all depends on how much current the source can deliver.... Good chance the small IC wire will blow free at one end or the other.

As for connecting a separate ground wire from the preamp to each amp I doubt that will help with the ground loop hum. It appears to me you would just be putting another conductor in parallel with the IC signal ground return. A current path is still provided for the ground loop.

I think the place to start might be at any dedicated branch circuit receptacles. Create a star ground for the PCs of any 3 wire cord and plug equipment. With a ground jumper wire connect the equipment ground of each recept together. Simple test would be to run a wire from each recept to the next using the metallic 6/32 trim screw that holds the recept cover plate on.
(Note, this will not work on isolated grounding type recept.)

Quick update here: I lifted the ground on each amp via cheater plugs and voila...hum gone. Thanks for all the advice, and I've learned quite a bit.