Isolating Digital Noise, need help.

ptss,
yes, using cheater plug on the Audience cable from ARC CD will get noise.

@jea48,
First, thank you for the tip on checking continuity of the two cables. They both test with a beep using the Continuity Setting.
Using the Resistance setting, both test close to zero.

As far as my understanding of ground loop, when two devices are plugged into mains power (both grounded), then connected together by an unbalanced cable, there will be current running thru that cable to each component. Is this correct?
BTW, the section on audio ground-loops in the Whitlock paper starts on page 56.

jea, I didn't try the cheater on the amp. I didn't think it was a good idea to lift the ground since it is a high power/current amp.

I will test the resistance on the Sunfire tomorrow, good idea. FYI, this amp was built in 1998 and has a fixed 3-prong AC cable. The next generation amp included an IEC cable.

Hi Lowrider,

I’ve just read through this thread. First, let me summarize some of the key points I’ve perceived:

1)The problem does not occur in any of the following cases:

(a)The CDP’s stock power cord is used instead of the Audience power cord.
(b)The CDP is connected to a more distant outlet. When you did this, how was the connection implemented (e.g., with a long extension cable attached to the Audience cord)?
(c)A different CDP is used.
(d)A different preamp (the prior one) is used.

2)The CDP’s stock power cord does not provide the open soundstaging and depth of the Audience power cord.

3)You will be demo’ing an SR power cord.

4)No ground loops are present, because:
(a)There is a Jensen transformer between the CDP and the preamp.
(b)There is a cheater plug on the preamp’s power plug, which eliminates the possibility of a ground loop between the preamp and the power amp.

5)Ideally you would prefer a solution that in addition to resolving the issue isolates the AC power provided to the digital components from the AC power provided to the analog components, because you anticipate purchasing a DAC.

Questions and suggestions:

1)If you haven’t already, it might be worthwhile trying the CDP’s stock power cord on the preamp. A reasonable speculation would be that the CDP’s stock power cord, as well as the extension cord I presume you used when you connected the CDP to a different outlet, resulted in higher series inductance than when using the Audience cord into the normal outlet, which in turn provided some degree of filtering of high frequency digital noise, that is causing the problem by coupling into the preamp through its power cord. So perhaps putting the CDP’s stock power cord on the preamp would resolve the problem, while not causing the sonic degradation you observed when using that cord on the CDP.

2)Are you sure that when you changed between the Audience and stock power cords on the CDP, and when you tried connecting the CDP to a distant outlet, that the physical proximity between those power cords and the preamp was not changed significantly? And that in all of those cases the CDP’s power cord has not been positioned close to the preamp or to the preamp’s power cord or interconnect cables?

3)For that matter, how close is the CDP to the preamp, and if they are close together have you tried moving them further apart? Although it seems likely that the noise is coupling through the power wiring, I don’t feel 100% certain of that at this point, and I wouldn’t rule out the possibility that radiated interference is contributing.

4)Regarding power isolation or filtering between digital and analog components in anticipation of obtaining a DAC, my feeling is that perhaps you should cross that bridge when you come to it, and not necessarily as part of the process of resolving this problem. For one thing, the optimal approach at that time may be DAC-dependent, requiring greater or lesser degrees of isolation or filtering depending on the particular DAC. And who knows, it may not even be necessary to provide any.

Good luck. Best regards,
-- Al