@xti16, good question. I am hearing this noise since I added a new preamp (Atma-Sphere UV-1) which is much more transparent than the previous one and has higher gain.
What's interesting is that it is so resolving, I can hear the change in noise from the power grid at different times of the day. I have a dedicated line, but live in the city. Late at night, the line is quiet.
It's an ARC CD3 mk II which is SS. And to answer xti16, I use a Jensen Iso-Max transformer to help with a ground-loop issue. It does cut the level of the high-pitched whine, but not completely.
I will be adding a DAC, so I need a plan for expanding my digital and to keep it isolated.
@jea48, yes I've used a cheater plug. You helped advise me on my dedicated line thread, where I wanted to add a line to remove a ground-loop between the amp and the preamp. Since I'm using unbalanced interconnects, the consensus was that an additional line would not guarantee the removal of the ground-loop.
I haven't installed that line yet since the layout of my circuit box is a mess and can't afford the electrical work at this time. So I'm using a cheater-plug on the preamp, as much as I don't like the idea, and a Jensen on the CDP.
My PC on the CDP is an Audience PowerChord, but I can try the stock cable for a test.
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@jond, the output of the ARC is high; 2.7V unbalanced. But the Atma-Sphere has a switch for -6dB attenuation on the input.
With the Audience PC, had the cheater on and off; still had the high-pitched noise.
Stock cable, no cheater plug.
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jond, yes, I’ve heard it the whole time. It took me a while to track down where it was coming from.
I have excellent upper frequency hearing and there has been a constant high-pitched "whine" in my house whenever my system was powered up. I have tinnitus, so at first I thought it was me. I finally put my ear near the tweeter to find it.
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@jea48, 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. There's been a miscommunication. When I referred to the ground-loop problem, I left out some of the back-story. When I first installed the Atma-Sphere preamp, it was using a 3-prong grounded plug (tried both stock and aftermarket). The amp was using a 3-prong stock cable and both were plugged into the same 20a dedicated line. The result was a 60 Hz ground-loop hum. I understand the principle of ground-loop in this case because they are connected by an unbalanced line. The only way to eliminate the hum was to run the preamp with a cheater plug. The strange part is that my previous preamp (Rogue Audio), was hooked up this way with no hum. Stock 3-prong on amp, Audience 3-prong on preamp, unbalanced interconnect. In that thread, either you or Al directed me to the Whitlock paper and I learned that the concept of using 2 dedicated lines may not eliminate ground-loop when using unbalanced cables. There is no cable TV and during this period, the power conditioning was removed. I'm going to look for my multimeter tonite. |
jond, I've had to use the cheater on the preamp from the beginning due to 60Hz hum. Spoke to Ralph at Atma-Sphere and Almarg and the problem is due to ground loop thru unbalanced cables.
The Jensen Iso-Max didn't work on the preamp, there was still low-level hum and it changed the sonics of the preamp.
The ARC is the issue. No noise when using my backup NAD CDP.
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@jea48, 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 stock PC sounds pretty good thru my power conditioner, but lacks the open soundstaging and depth of an audiophile PC.
I actually have a Synergistic Research Black PC on order for demo.
Since I'll be adding a DAC, I will still need to isolate digital from analogue components. Is a dedicated line the only way?
Also, I still need to work on the ground-loop problem between amp and preamp, and that will require a separate AC line.
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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. |
@jea48,
First, thank you for the tip on checking continuity of the two cables. They both test with a beep using the Continuity Setting.
Using the Resistance setting, both test close to zero.
As far as my understanding of ground loop, when two devices are plugged into mains power (both grounded), then connected together by an unbalanced cable, there will be current running thru that cable to each component. Is this correct?
BTW, the section on audio ground-loops in the Whitlock paper starts on page 56.
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ptss,
yes, using cheater plug on the Audience cable from ARC CD will get noise.
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jea, I didn't try the cheater on the amp. I didn't think it was a good idea to lift the ground since it is a high power/current amp.
I will test the resistance on the Sunfire tomorrow, good idea. FYI, this amp was built in 1998 and has a fixed 3-prong AC cable. The next generation amp included an IEC cable.
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@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.
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I hooked up the Pangea PC to the ARC CDP and I'm getting the same high-pitched noise as with the Audience cable.
After several A/B tests, there is noise when using the stock PC, but less audible than with aftermarket cables.
So it leaves me to wonder if I should try an isolated power strip. Right now all my components run thru the Blue Circle and then to a Furman EMF/RFI strip except for the amp. Or is there a filter or power cord for digital devices?
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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. |
@jea48, What does the meter indicate when both test probes are touched against
one another? "L"? There in as "short" or "000.0", continuity? touching probes together shows 000.0 continuity. I made a mistake, it always indicates "0L" when there is no reading. I downloaded the manual for the meter. https://equus.com/Content/Support/Manual/93-0041.pdfWhat 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? the same. 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?
Correct. CDP is not connected to inputs. 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? I guess I was under the impression it was plugged in the audio system wall outlet when you switched to the stock power cord. Yes, the stock PC was connected to the wall behind the system. |
@tbg , no, amp is quiet.
@jond, I'll try that today, the cable from the Furman may reach across the room.
Thanks. |
@jea48 Check again for resistance from the ground pin on the power cord plug to the metal chassis of the amp. "OL"? Yes, OL (or zero L). Maybe a code for something? 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? 1.0 for resistance. I have looked on Carver/Sunfire forums for a schematic and no luck. Others are asking for them and apparently the company has never released them to the public. Many thanks for interest thus far. |
Well, I have some test results to report.
I used an AC receptacle across the room as a second line to separate the components from the amp. It is a shared circuit with ground.
The amp was plugged into it’s dedicated line and the Furman strip with preamp (using cheater-plug), and CDP was plugged into this 2nd line. Both components using Audience PC’s.
1. The result was no high-pitched noise from the CDP. This was tried with the Jenson transformer in-line and also removed. Result was the same; a quiet tweeter.
So, I believe this proves that the ARC CDP is introducing noise into the shared dedicated line and needs to be isolated.
2. Ground-loop issue: used a 3-prong PC from the preamp into Furman and into 2nd AC line.
The amp is plugged into dedicated line with 3-prong (usual setup).
The result was a low-level hum thru the speakers and not the loud 60Hz hum.
The amp is now known to have a grounding issue, but is it possible that that this low-level hum could be due to the fact that the second line’s grounding is unknown?
IOW, I think it is worth running another dedicated line. Ideally 3 lines would be best, but cost is an issue.
Your thoughts?
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Thanks, jea48. First of all, that is my amp...Sunfire 300 Load Invariant. 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". That's correct. The digital scale measured 1.0 ohm +or- a couple units since the probes were hand-held. It never approached zero. I've never had the top off, but it was serviced 3 years ago and maybe the wire could have come off. I'll have to wait til I have some time to devote to opening it up since the amp is not easily removed from my rack. I built a custom shelf for it. 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. I will do this tomorrow. It seems that you and Ralph are right about the amp not being properly grounded. I assume you have the jumpers installed in XLR female connectors. I've never heard any mention of using jumpers on this amp; not in the manual or on Carver/Sunfire forums. Can you explain? I know that this amp is SE and the RCA and XLR are wired in series. The next generation of the 300 amp is supposed to be fully balanced and has specs to indicate this. My amp only has a single input sensitivity of 1.64V. |
thanks Al. Will do tonight. |
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.
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jea48 and Al,
Checked continuity between RCA center pin and pin 3 XLR... OL
Same as the previous test for RCA to pin 2 XLR... OL
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.
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.
As far as the readings I'm getting, do I need a better multi-meter?
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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?
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Many thanks to both of you.
I've been ill for a while and going thru some treatment, so when I feel better I'll open up the amp. That's why I was looking for a quick fix with a power strip. Until then, I'll run my components off a 2nd outlet which eliminated the digital noise.
With your assistance, I now believe the amp may be the root cause of all the issues I'm having with my system. I'll update you once I'm able to pull the amp out for inspection.
Thanks again, Al and jea48. And btw, I ordered the Cardas shorting pins.
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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. We discussed my ground-loop situation with the preamp and he said he would try to contact Bob Carver to find out the reason for this design and if it can be modified. In the meantime, I found this on Pass Labs website... In order to minimize ground loop issues Pass Labs never manufactures equipment with signal ground and chassis ground contiguous.
By separating signal ground and safety grounds, connecting units together should never cause ground loop issues; however, not all manufacturers follow this line of thinking.
Regarding the noise produced by the CDP thru the power line, I purchased a Tripp Lite isolated power strip since it is intended for computers and digital devices. http://www.amazon.com/gp/product/B0000513O4/ref=ask_ql_qh_dp_hzaMy findings... - Furman and Tripp Lite both plugged into Blue Circle conditioner. - Atma-Sphere preamp w/ Audience PC plugged into Furman, CDP w/ Audience PC plugged into Tripp Lite. The result was high-pitched noise was still present thru the system. Next, I swapped preamp into Tripp Lite; CDP into Furman... The result was high-pitched noise eliminated. Preamp is no longer using a cheater-plug, but there is low-level hum due to the amp. I've been playing CDs for 3 days and there has been no noise from the CDP. I don't understand why the digital noise is eliminated with the preamp in the Tripp Lite, but it works and CDP sounds smooth w/o the Jensen transformer. |
You're right, my tests indictate that the chassis is not grounded. He said the grounds should meet at a certain point and he will need to look at it. Also do to age it should be serviced, so I've packed it up to ship to him.
Will discuss grounding pins after he inspects it. |
