Isolating Digital Noise, need help.

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

lowrider57, I think that others may have already suggested what I would do first. 

Disconnect the interconnects from the amp and turn it on, If there is no noise, it is something upstream. If it still hums it is the amp, of course. 

Next add the line stage with both it and the amp on. If it doesn't hum, it is the line stage. If still no hum it is one of the sources. 

If it doesn't hum with one source but not the other, well you know. I think  you may have already done this and suspect the digital source. I would put a cheater plug on the amp if you find it is the digital source. If no hum with the cheater, you have ground loops. I would use cheaters on everything except the line stage.

Possibly the Blue Circle FX2XOE (that has 3 pair of outlets) would filter out the problem. The only reason I'm suggesting this is because I use one to correct a problem I had in my secondary system. It worked out so well, I purchased a second one that is brand new but I have not needed to use it. If other suggestions don't work you could try mine.

@jea48
I did some tests on the amp. With my multi meter, measuring from the male ground pin on the Sunfire amp to the metal chassis of the amp, I could not get a reading of resistance. The meter indicated “L.”
It is a digital meter with no multiplier for scale.

Bypassing all power conditioning, I plugged the amp 3-prong into the wall, and plugged the stock preamp 3-prong cable into the wall; result was 60hz hum. I used Belden Interconnects instead of audiophile brands.

Using a cheater plug on the amp plugged into the wall and stock preamp cable plugged into wall, I can hear a noisy power line when I put my ear up to the speakers.
FYI, there is no transformer hum emanating from this amp.

Hi Al,
Addressing the CDP high-pitched noise issue:
You are correct. I will provide some further info;
The CDP is connected to a more distant outlet... I used a heavy-duty extension cord with the Audience PC and ran it to a dedicated receptacle for the washer/dryer in the basement. So it was about a 25 ft. run.
I will do this test again with a closer outlet, but they are all typical shared AC lines found in the home.

Regarding ground-loop:
Correct.
The Jensen does remove some of the high-pitched noise. Removing the Jensen is when the noise is at a high level and can be heard thru quiet passages of Classical music.
The reason I remove the Jensen is because the input IC affects the sonic signature of the CDP plus Purist Audio output IC. I am continuing to experiment with ICs for the Jensen input, but the timbre of my system is best w/o the Jensen and a cheap cable. I’m dealing with a double-edged sword.

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

You’re probably right, that’s why I’ll repeat my test using a closer outlet. I used the basement receptacle because it is a dedicated line that I trust.

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?

No change in position, and power cords are separate from audio cables. But the preamp and CDP PCs are definitely close to each other.

how close is the CDP to the preamp, and if they are close together have you tried moving them further apart?

The CDP is on the top of the wood rack unit (position #1), the preamp is on the 3rd shelf (position #3). Ralph and I discussed placement when I called him regarding hum/ground-loop. The preamp is not in proximity to any transformers.

Al, I appreciate the time you’ve spent on this. I would really like to find the answer to this digital noise problem. I just realised that I have a Pangea PC that I’m not using...this will be my next test on the CDP.