Isolating Digital Noise, need help.

UL says the equipment ground must be connected, bonded, directly to the chassis doesn’t it?

In any event, it is strange indeed that the Sunfire amp connects signal ground and safety ground together but not to chassis. If it happens to be connecting the grounds to chassis via a capacitor, though, it would explain why the meter reads OL between the grounds and chassis. But it still would not explain the safety issue that would presumably result from the lack of a direct connection between safety ground and chassis.

jea, since you commented on the high gain of the CDP (2.7V), I checked it by playing thru a different preamp input and the gain is too high. Ralph put in the -6dB pad for me as a mod due to the CDP’s high gain spec. And it sounds very good.

Al, (almarg), has ruled out the CDP 2.7V output as being the problem. Reread Al’s response to my post above. Also as stated by you, Ralph, (the owner of Atma-Sphere), modified the preamp, for you, to handle the 2.7V input to the input section of his designed preamp.

CDP...
I used the 25 ft. heavy-duty ext. cord with the Audience PC plugged into the Furman strip with preamp today and into the dedicated line, (no power conditioner). The high-pitched noise presented after the components were warmed up. The noise was not as loud, but is still audible.
Tried it with and w/o Jensen Isomax at CDP’s output. The Jensen does lower the level of the noise, but it’s still objectionable.

At this point you are just going in circles. If the hi-pitched noised is being caused by the ARC CDP sending digital hash, noise, harmonics, or what ever it is, back out on the power cord and then reinterring the power cord of the preamp or possibly even the power amp, and thus causing the hi-pitched noise, it is possible that is the cause of the noise.

The bigger picture though, in my opinion, is the multiple problems with the power amp. I think all the problems with the amp must first be resolved. The equipment ground issue is critical as well as the balanced XLR jacks on the amp needing the jumpers installed for the amp to operate as it was designed.

Who knows maybe the amp has been the problem all along.

And I just thought of something. I bought my amp used from a HiFi dealer; it was his personal amp. Could he have lifted the ground for use in his system?

Another reason to pull the top cover off the amp for a look inside.

**NOTE: Naturally unplug the amp from the AC power. It would also be a good idea not to stick your fingers inside the amp for at least a half hour or so for the electrolytic caps in the DC power supply to bleed off, discharge. One hour if you really want to be safe.

Look at where the power cord enters the amp’s rear panel. Look for the green insulated equipment grounding conductor, wire, from the power cord. It should directly connect to the metal chassis of the amp. From your test measurements it does not. What I don’t understand though is, why, where, or how, it is still connected to the B- rail/signal ground of the amp. (Going by your test measurements.)