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.
For a test did you try using a ground cheater plug on the ARC CDP? I would suggest you try that first. It sounds to me from your post the power supply of the CDP is corrupting the power supply/s of the analog equipment. You might look into a power conditioner for the CDP to isolate the CDP power cord from the analog power cord/s. Does the ARC CDP have a detachable power cord? If so are you using the stock power cord that came with the CDP or an aftermarket power cord? If it is an aftermarket power cord you might want to make sure it is wired correctly. Make sure the Hot and Neutral conductors AC polarity are not flipped from the plug and the IEC connector.
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so far there is no high-pitched noise when using the stock PC on the ARC. Perhaps the Audience PC is not a good design for a digital device?
The IEC connector is probably wired wrong. The Hot and neutral conductors are probably switched, interchanged. You can check it with a meter. Just check for continuity.
Simple way is to use the stock cord that came with the ARC CDP. Check plug blade to IEC contact for feed through continuity. Then compare the Audience PC to that. The ARC stock cord is the correct plug to IEC polarity orientation.
Also, I still need to work on the ground-loop problem between amp and preamp, and that will require a separate AC line.
If both the preamp and power amp are plugged into the same wall outlet duplex receptacle and you get a ground loop hum now, then more than likely you will sill get the same ground loop hum with a dedicated AC line. Beats me how you can get a ground loop hum from the AC mains safety equipment grounding conductor if only one AC mains system equipment ground is involved. It takes two tangle. Where is the other AC mains system equipment ground providing the difference of potential, voltage, needed for the current flow to produce the 60Hz ground loop hum? No difference of potential, no current flow, no hum. What power cords are you using on the preamp and power amp? Stock, or aftermarket? If aftermarket try the stock cords that came with the equipment. Is the audio system in any way connected to a Cable TV system or Satellite
dish system? And what's with the power conditioner? You didn't mention anything about a power condition in previous posts. Try removing the power conditioner and plug the equipment directly into the wall duplex receptacle. Remove the ground cheater, check for ground loop hum.
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jea, I hope that's a rhetorical question, because I'm going by what I read in the Whitlock paper.
Ralph thinks my Sunfire amp may have an atypical grounding design.
No, I did not mean it as rhetorical question at all. (I assume the ICs are not long.)
I understand the principle of ground-loop in this case because they are connected by an unbalanced line.
Not that I doubt you read it. Where did you find that in the white paper? We are not talking about noise.
https://centralindianaaes.files.wordpress.com/2012/09/indy-aes-2012-seminar-w-notes-v1-0.pdf I think Ralph is probably right about the Sunfire grounding design and somehow that is causing a difference of potential, voltage, to exist between the two safety equipment grounded chassis. Thus current flow, 60Hz ground loop hum. Just curious what happens if the ground cheater is placed on the amp and not on the preamp? Did you ever try it that way? When you find your multi meter I would also be curious to know, if from the IEC male ground contact pin on the Surfire amp if there is any measureable resistance from the IEC ground pin to the metal chassis of the Amp. There should not be any resistance. The meter should read short. (Disconnect the ICs from the preamp when do the test. Shouldn't make any difference but it totally isolates the amp from anything else.) |
I understand the principle of ground-loop in this case because they are connected by an unbalanced line.
Please explain it to me, because I don't understand it. |
Lowrider57 said:
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.”
"L" ? What does the meter indicate when both test probes are touched against one another? "L"? There in as "short" or "000.0", continuity? >>
Lowrider57 Said:
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.
To be 100% clear here, you did say the ground loop hum is being caused when only the preamp amp and amp are connected together by ICs. Is that correct? The CDP is not in the ground loop, possibly being the culprit causing the ground loop hum, correct? To be 100% sure that is the case, disconnect the CDP ICs from the preamp and check for ground loop hum. (Ground cheater not used on preamp or amp.)
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For clarification.... You said earlier when you used the stock cord that came with the CDP the high frequency "whine" sound was gone. Where was the CDP fed from then? From the basement laundry room receptacle, or from the receptacle by the audio system where it normally is plugged into? I guess I was under the impression it was plugged in the audio system wall outlet when you switched to the stock power cord.
>> Lowrider57 said:
First, thank you for the tip on checking continuity of the two cables. They both test with a beep using the Continuity Setting.
Continuity? What I want to know are the plug to IEC pin out connections
for the aftermarket power cord, the same as the ARC stock power cord? |
Lowrider57 said:
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.”
So "OL" equals open? Same as the meter reads with the probes not connected to anything? Check again for resistance from the ground pin on the power cord plug to the metal chassis of the amp. "OL"? Next measure from the ground pin on the plug to one of the outer grounds of one of the RCA jacks on the back of the amp. (No ICs connected to the inputs of the amp.) Any resistance? "OL" ? What is the model number of the amp? Do you have a wiring schematic diagram for the amp? |
Yes, OL (or zero L). Maybe a code for something?
If you do not measure 000.0 or in otherwards "short", or continuity, then for some reason the metal chassis of the amp is floating above the safety equipment ground. That does not meet any equipment electrical safety standards/requirements. What is odd though, from your measurements, the safety equipment grounding conductor of the power cord is connected to the signal ground. You measured 1 ohm of resistance. Correct? That’s basically "short". Have you ever removed the top cover from the amp before? If you can remove the top cover,. then look at the back where the power cord enters the back panel. Look for the green equipment ground wire of the power. Is the wire broken free from the metal chassis? It should connect directly to the metal chassis.
One other test measurement I should have had you check. From what you have said thus far the result should already be known. I still would like to have you check. Check for continuity from the outer contact of one of the RCA input jacks to the metal chassis. It technically should read "short", "000.0", continuity. But from what you have said from the measurements you have taken, you should read "OL" open circuit. The signal ground is not connected to the metal chassis. IF the chassis if floating above the signal ground as well as the safety equipment I would think that could cause buzz/hum problems. And then there is the coupling capacitance leakage of the primary to secondary winding to consider.
Is this what your amp looks like?
https://www.google.com/search?q=sunfire+stereo+amplifier&rlz=1T4GGLL_enUS413US413&tbm=isch&a...
http://s26.postimg.org/j4ws3i4jd/Sunfire_002.jpg
I assume you have the jumpers installed in XLR female connectors.
http://img.usaudiomart.com/uploads/large/689209-sunfire_stereo_power_amplifier_300_wpc.jpg |
ARC CD2 wiring schematic wiring diagram. http://www.audioresearch.com/ContentsFiles/CD2%20Sch%20pl%20tips.pdf >> XLR shorting jumper.
http://www.cardas.com/images/cgsp_pic1_transparent.jpg >>
Decoupling the power supply of digital from analog.
Quote from the late Robert Crump:
Solid core Romex has an absolute ton of inductance and you can use that to roll off the digital backwash and end up isolating your analog from digital with yards of the solid core Romex in the walls. Romex is insulated with PVC and, again I will say that PVC is what you want rather than anything faster as you just want to pass 60hz and attenuate anything above that.....Stranded wire, especially a twisted lay, will pass high frequencies better, exactly what you don’t want to do with 60hz AC.......Regarding power cords made with PVC it apparently works pretty well as have sold over 8,000 of them the past 21 years.......
You aren’t looking at this correctly........ - rcrump - Cable Asylum »
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lowrider57 said:
@jond, the output of the ARC is high; 2.7V unbalanced. But the Atma-Sphere has a switch for -6dB attenuation on the input.
Al, What are the chances the ARC CDP is still over driving the L & R input stage of the preamp? Also look at the ARC CDP output section. Transformers are used.
http://www.audioresearch.com/ContentsFiles/CD2%20Sch%20pl%20tips.pdf Does that mate well with the input section of the preamp?
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- 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.) |
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 |
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.) |
UPDATE...
I spoke to the owner/tech of the only authorized Sunfire service center regarding the grounding design of their amps. He said in a Sunfire amplifier that the chassis, power and signal ground are connected together.
But yours is not. Through your testing you found the chassis is not connected to either the safety equipment ground wire of the power cord or the power supply signal ground. What did the tech say when you told him that? How about the shorting/connecting jumpers for the XLR connectors? Did you ask him if the amp needs them installed when using the amp with single ended RCA ICs? |
