Isolating Digital Noise, need help.

Jim (Jea48), you provided an excerpt and a link to Mr. Hansen's statement in the last post on this page. However, I would not interpret his statement to mean that signal ground should be connected **directly** to the chassis, as that can be conducive to ground loop issues. Preferably signal ground should be connected to the chassis through a low value resistor (e.g., 10 to 100 ohms). As you've probably seen, for example, a lot of ARC designs use 10 ohms.

Al,

Thanks for pointing that out. When the equipment uses the safety equipment ground the designer of the equipment, in most cases would not connect the signal ground directly to the chassis. Arc uses a 10 ohm resistor as well. Somewhere in the thread Link you provide I think I mentioned that.

Here again is the actual statement of Charles Hansen's 

The only way that the case can provide any shielding for the audio circuitry is if it is connected to the signal ground. In addition, if it is left unconnected from the signal ground, then it will create unwanted capacitive feedback loops (both positive and negative) between various parts of the circuitry. Refer to Morrison's books for additional details.

 
http://www.audioasylum.com/audio/general/messages/52/525622.html 

Here is the entire AA posted message. 
http://www.audioasylum.com/audio/general/messages/52/525276.html

In any event, it is strange indeed that the Sunfire amp connects signal ground and safety ground together but not to chassis. Although if it happens to be making the connection to chassis via a capacitor, it would of course explain why the meter reads OL.

UL says the equipment ground must be connected, bonded, directly to the chassis doesn't it? Of course we don't know if the Amp is UL Listed, or was safety tested by any recognized third party testing laboratory.

Off subject,  I was on another audio forum last week and learned there is a well know US audio manufacture, (I will not mention the name here), that provided a ground lift switch on the back of one of his amps. The switch doesn't lift the signal ground from the chassis. It lifts the safety equipment ground wire from the chassis. Obviously the amp is not Listed by any recognized third party testing laboratory.

Jim

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.