Isolating Digital Noise, need help.

Well, I have some test results to report.
I used an AC receptacle across the room as a second line to separate the components from the amp. It is a shared circuit with ground.
The amp was plugged into it’s dedicated line and the Furman strip with preamp (using cheater-plug), and CDP was plugged into this 2nd line. Both components using Audience PC’s.

1. The result was no high-pitched noise from the CDP. This was tried with the Jenson transformer in-line and also removed. Result was the same; a quiet tweeter.
So, I believe this proves that the ARC CDP is introducing noise into the shared dedicated line and needs to be isolated.

2. Ground-loop issue: used a 3-prong PC from the preamp into Furman and into 2nd AC line.
The amp is plugged into dedicated line with 3-prong (usual setup).
The result was a low-level hum thru the speakers and not the loud 60Hz hum.

The amp is now known to have a grounding issue, but is it possible that that this low-level hum could be due to the fact that the second line’s grounding is unknown?
IOW, I think it is worth running another dedicated line. Ideally 3 lines would be best, but cost is an issue.

Your thoughts?

I believe this proves that the ARC CDP is introducing noise into the shared dedicated line and needs to be isolated.

Yes, but per my previous post perhaps the extension cord itself would provide sufficient isolation, when plugged into the outlet that is normally used. Seems worth trying, on both the CDP (the source of the noise), and the preamp (which is probably where the noise is causing the trouble).

The amp is now known to have a grounding issue, but is it possible that that this low-level hum could be due to the fact that the second line’s grounding is unknown?

That is very conceivable. Jim (Jea48) has previously provided us with a link to a paper by Bill Whitlock (the Jensen Transformer person, although he may be retired now) in which it is explained that ground loop hum is usually caused or contributed to by coupling of EMI between the hot & neutral wires and the safety ground wire in the house wiring. Which occurs very minimally with Romex, due to its symmetrical design, but occurs to a much greater degree with wires in conduit. Is there any way to determine what kind of wiring is used between that outlet and the breaker panel?

Also, Jim (Jea48) makes a good point about jumpers. Given that there is no balanced/unbalanced switch on the amp, and that it has an unbalanced internal signal path, I suspect that jumpering pins 1 and 3 together on each XLR connector might be helpful, with respect to hum and/or sonics. Check for continuity between the center pin of each RCA connector and pin 2 of the corresponding XLR connector. Also check for continuity between the ground sleeve of each RCA connector and pin 1 of the corresponding XLR connector. I suspect you’ll measure close to zero ohms in both cases. If so, I would suggest that at some point you obtain some solid core wire of a gauge that would provide a snug fit and use it to jumper pins 1 and 3 on each XLR connector.

BTW, "OL" is most likely derived from either "out-of-limits" or "overload," and when you are measuring resistance signifies that the resistance is greater than the 20 million ohm upper limit of what the particular meter can measure. In other words, an open circuit.

Best regards,
-- Al

thanks Al. Will do tonight.