2. tech-talk
  3. 123848-2280

Isolating Digital Noise, need help.

I'm hearing noise from my ARC CDP thru my speakers presenting as a high frequency "whine" or "soft screeching." I need to isolate my digital from the AC line it shares with my analogue components. Running another dedicated line is not an option at this time.

I was wondering if a power strip with isolated receptacles, such as star-grounding, would be an alternative to a separate AC line.
As a test, I now have the CDP connected to a different outlet in my house and the noise thru my system is eliminated.

Would this type of power strip be an effective solution, and if so, I could use some recommendations. I have several layers of Blue Circle power conditioning, so I would need a strip with surge/EMF/RFI protection.
128x128lowrider57
lowrider57's avatar
lowrider57 OP
5,417 posts
 
Al and jea48,
I really appreciate the time you've devoted to my situation.
I was out all day, but was able to take some measurements:

- continuity of RCA outer sleeve to metal chassis... reads OL
- continuity of each RCA center pin and pin 2 of XLR... OL
- continuity of RCA outer sleeve and pin 1 of XLR... 000.0

Al, I looked at the 20a dedicated AC line and it appears to be a 12/2 generic cable. I looked at the electrician's invoice from years ago and it is itemized as a Refrigerator line, dedicated 20a circuit.
If you recall, I had a thread where I asked for advise on the proper installation of a dedicated line. That's when I discovered that the electrician placed this wiring near the top of the circuit box and close to the furnace and appliances. So, when I add another line, I will need to have the box reconfigured.

And jea, thanks for the pic of the Cardas jumpers. I found them online and will order them.
jea48
4,425 posts
 

- continuity of RCA outer sleeve to metal chassis... reads OL
- continuity of each RCA center pin and pin 2 of XLR... OL
- continuity of RCA outer sleeve and pin 1 of XLR... 000.0

- You said in an earlier post you checked for continuity from the ground pin of the power cord male plug to the metal chassis of the amp and the meter display read "OL"..., Open, no connection. Correct?

IF the RCA jack outer sleeve to the metal chassis reads OL then the signal ground is not connected to the chassis. You said in an earlier post the safety equipment grounding conductor of the power cord is not connected to the chassis either.

I will have to search the archives of AA for a post of Charles Hansen, owner of Ayre Acoustics, but that’s a no no. Something about capacitive feedback loops. Or something like that. At any rate I think it can add hum/buzz on the signal of the amp. (Without rereading all this thread, did you ever have the amp turned on without anything connected to the inputs of the amp? That thing should hum/buzz like crazy I would think. Especially if a ground cheater was used on the amp plug to wall receptacle.)

I am still confused why you measured 1 ohm of resistance, basically continuity, from the ground pin on the plug of the power cord to the outer sleeve of the RCA on the amp. That means the signal ground of the amp is connected to the equipment grounding conductor, wire, of the AC power cord.

You really need to address the problem/s with the amp first before you do anything else. You need to pull the top cover and see why the safety equipment ground of the power cord is not solidly connected to the metal chassis of the amp. Why it, the safety equipment ground wire, is some how connected to the signal ground. Both the signal ground and safety equipment should be connected to the metal chassis of the amp.

(Note: I see no user ground lift switch on the back rear panel of the amp for user preference.)

almarg's avatar
Ag insider logo xs@2x
almarg
9,670 posts
 
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.

My VAC amp, btw, has a three position switch controlling that connection. One position connects signal ground and chassis directly; one position is described as connecting them at audio and higher frequencies but not at DC (presumably via a high value capacitor, perhaps in combination with a resistor); and one position is described as connecting them only at RF frequencies (presumably via a low value capacitor, perhaps in combination with a resistor). The AF and RF positions seem to sound slightly better in my system than the DC position, and I’ve settled on the AF position (which the manual recommends as the one to start with).

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.
continuity of each RCA center pin and pin 2 of XLR... OL
Check for continuity between the RCA center pin and pin 3 of the XLR connector. If that measures near zero ohms, you would want to put the jumper between pins 1 and 2 of the XLR connector.

If that also reads OL, however, it would probably mean that the XLR and RCA inputs are received by separate receiver stages, in which case it would be ideal (although perhaps neither necessary nor practical) to jumper both pins 2 and 3 to pin 1. Or, in that situation (both pin 2 and pin 3 read OL relative to the RCA center pin) you could try jumpering each possible combination of two pins together (1 to 2; 1 to 3; 2 to 3), assessing the three possibilities one at a time.

Best regards,
-- Al


jea48
4,425 posts
 

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

almarg's avatar
Ag insider logo xs@2x
almarg
9,670 posts
 
Thanks, Jim. Regarding ...
UL says the equipment ground must be connected, bonded, directly to the chassis doesn’t it?
... Shortly after submitting my post, and shortly before you responded, I revised the paragraph you quoted from as follows:
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.
Best regards,
-- Al

More to discover