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PC - DAC ground loop (GPU culprit)

Vasr

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2) If I lift the ground of the wall socket where the TP is plugged in (that is to say, all audio gear), but my DAC is connected to the PC by the USB cable, wouldn't that connection work as a shunt to the grounded wall socket where the pc is connected?

3) In Argentina, all buildings have circuit breakers installed. I'm not an electrician, but in the event of a non-grounded device malfunctioning and letting the current go through the chassis, wouldn't this circuit breaker cut all power?

Typically, you don't want audio signal cables to act as the safety electrical ground (let us call it "earth ground") for the equipment as they tend to be connected to rather sensitive components and even a momentary high-voltage surge through them can damage things or they may melt and leave the equipment ungrounded. The ground loop in the signals we are hearing and trying to fix are in the order of mVs to a volt, not the 110 or 220v electricity supply.

Part of the confusion in this area comes from the use of the "ground" in two different contexts - as the "safety wire" in case of electric shorts of the main power to the equipment chassis which may create a shock hazard ("earth ground") and the "signal ground" which is the reference ground used for the circuitry and the audio connectors (or even in a balanced connector wired incorrectly). In most equipment (but not necessarily), they both happened to be connected to the chassis as a common conductor. Some audio equipment provide a switch to lift the ground of the signals if necessary, which just separates the signal reference ground from the "earth" ground. Some equipment do this all the time. The "earth" grounding for the main supply connected to the chassis remains the same in these and unrelated.

The "earth" ground for the main power is always connected to the chassis (if conducting material) to handle the case if a live main gets shorted to the chassis inside a device and makes the chassis live and a shock hazard. For this to work, the chassis through the third ground pin will have a low resistance path to the electrical circuit. So, if the live electric wire gets shorted to the chassis, it creates a surge within the live wire through the ground pin that will trip circuit breakers and/or blow out fuses as a safety measure. Without it the chassis is not "earthed" to affect the circuit breakers or fuses. So a short of the live wire to the chassis without a ground pin will just make the chassis live without tripping circuit breakers and a shock hazard.

The schuko plug will simply act as a two-pin plug without the ground attached if the ground clip isn't mated to a corresponding receptacle which is likely what is happening in your case. So you would no longer have that ground protection.

The ground loops (at signal level not in the electrical circuit) happen because there may be a small electric potential between the grounds of two equipment connected to their respective "earth" grounds with different impedance paths to the connector shields (signal grounds). So you have ground loop currents flowing through the signal "ground" affecting the sensed signal. This is more of an annoyance than a safety issue.

This can be solved if the signal is sent through a galvanically-isolated connector, or made differential as in a correct balanced connector, or the unbalanced signal ground is disconnected from the "earth" (chassis) ground or the "earth" ground itself is grouped into a single path to eliminate that potential difference in the signal grounds between two devices when they are connected to "earth" ground in multiple devices.

The preference would be to try it in the order above to fix it. None of the fixes involve permanently removing the "earth" ground from any device. The ground shunt as a last resort connects the chassis/"earth ground" of two pieces of equipment together with a low resistance wire strong enough to carry main voltage so you can disconnect the ground from one device and have the ground pin from the other act as the safety ground for both. The surge through it in case of a short will trip circuit breakers. The audio connectors should not serve this purpose via their shields.
 

KSTR

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I got a bit lost here. Could you please clarify?
Ok, let's dig in there a bit deeper:
- The safety grounds (aka Protective Earth, PE) of the PC and the AMP are only nominally the same but actually they are different because any current on the PE (injected by internal mains filter caps, among other mechanisms) will produce a voltage drop accross the non-zero mains cable resistance and contact resistances.
- The Audio/Signal Grounds (GND) in both devices are tied to protective earth, directly or close to directly.
- The RCA interconnects try to short out that voltage and that will result in so-called balancing current to flow, again creating voltage drops on the interconnect shield.
- This voltage drop along the cable shield again represents an error voltage which appears directly as input signal for the amp. The amp just sees the difference voltage between the RCA center conductor and the shield, it does not care how this voltage builds up.
- Consequently, the lower the shield resistance, or more general, the lower the resistance between the audio reference grounds of DAC and amp, the lower the resulting noise voltage.
- Therefore, making additional ground connections between DAC and AMP will help the signal cables by sharing the current.
- Keeping the interconnects and these additional "ground bonds" as short as possible also has direct effect, its all about keeping the resistance (and inductance) at the lowest feasible value.
- On the primary side it's a bit more complex but the basic idea again is to provide additional ground bonds between amp and PC to tie them -- and hence their signal/audio grounds -- closer together, minimizing the voltage difference between their PE connections to begin with. More often than not, this has proven effective IME.
- To further reduce the offending balancing current, one might try to make the mains connection rather high resistance/inductance (in relative terms) without defeating the safety-earth concept(!!!) This can be done by using two long extension cords or even (unreeled) cable drums to feed two separated power strips, one for the PC and associated equipment and the other for the analog audio gear (including the DAC). Using a long (thus higher resistance) USB cable also increases the total resistance.
- If things happen to fall into place as planned by the above description, I would think you could easily drop the noise voltage level at the amp input by a factor of 10 or more (20dB++) which might be sufficient to become totaly inaudible. There is a small risk that the remaining balancing current (which still is flowing) could produce noticable residual noise in the amp's (or DAC's) circuit itself and therefore reducing the shield resistance to zero will not get rid of the symptom. I would think that the tube amp will probably have enough noise and hum all by itself to make that factor insignificant, though.

[...]Yes, I had tested this. When the usb is disconnected from either end, noise disappears. I do have a CD player with a toslink output, but what did you mean for me to try with it and the DAC?
Ok, so we can be sure it's a traditional "ground loop".
The test with CD player feeding the DAC's optical input was meant as an additional checkpoint to assert that optical connection to the DAC a) works basically and b) cures the problem, even with the lowest digital input signal levels. Then you can expect an USB->TOSLINK adapter to work equally well in case you decide to take that route.

Hope this helps.
 

rkbates

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I noticed a ground loop between my PC and my DAC. It's pretty much exactly the same described in this video (skip to 11:28). It also responds to locking fps and changes pitch accordingly.


This has been reported extensively across various forums. I'll just link to one nvidia thread, but I also saw it for AMD cards: {{MetaTags.og.title}}

I bought an IFI idefender, but not only did it not break the loop, but it also introduced a new hissing sound, so it's a no-go for me. I tried disconnecting everything except the PC, the DAC and the amp, and the ground loop persists. It even happens with the DAC disconnected from the current. Connecting the DAC to a laptop (and using the laptop's battery) doesn't produce the ground hum, so the DAC is not defective.

The only thing that breaks the loop is lifting the ground from either the PC or the power conditioner where all my audio stuff is connected to (I did try other extension cords with same results). I did try different power sockets in the room, same result.


Other than permanently lifting the ground from my audio gear, do you guys have any other suggestions?

Setup:
- PC: i5 8600k + asus z370-a prime + nvidia EVGA 1070 + 2x8 gb ddr3000
- Audio setup:
-- Audiowalle TP1000 power conditioner (AKA fancy power extension cord)
-- Vincent sv237-mk
-- DAC: SMSL m500
-- KEF R300
I had a listen to the video at 11:28 and this is not your typical 50/60Hz ground loop hum. Are you able to try a different PC?
 

rkbates

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When a ground loop involves a PC, noises often aren't dominated by mains hum - some people are only alerted to the presence of one when they start loading their GPU. In more severe cases you can even hear mouse movement.
Thanks - haven't come across this before. What root causes have you seen in these sort of cases?
 
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Dexter_prog

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I had a listen to the video at 11:28 and this is not your typical 50/60Hz ground loop hum. Are you able to try a different PC?
I tried a laptop and the hum wasn't there, but the laptop wasn't connected to the power socket
 

Mindcool

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I noticed a ground loop between my PC and my DAC. It's pretty much exactly the same described in this video (skip to 11:28). It also responds to locking fps and changes pitch accordingly.


This has been reported extensively across various forums. I'll just link to one nvidia thread, but I also saw it for AMD cards: {{MetaTags.og.title}}

I bought an IFI idefender, but not only did it not break the loop, but it also introduced a new hissing sound, so it's a no-go for me. I tried disconnecting everything except the PC, the DAC and the amp, and the ground loop persists. It even happens with the DAC disconnected from the current. Connecting the DAC to a laptop (and using the laptop's battery) doesn't produce the ground hum, so the DAC is not defective.

The only thing that breaks the loop is lifting the ground from either the PC or the power conditioner where all my audio stuff is connected to (I did try other extension cords with same results). I did try different power sockets in the room, same result.


Other than permanently lifting the ground from my audio gear, do you guys have any other suggestions?

Setup:
- PC: i5 8600k + asus z370-a prime + nvidia EVGA 1070 + 2x8 gb ddr3000
- Audio setup:
-- Audiowalle TP1000 power conditioner (AKA fancy power extension cord)
-- Vincent sv237-mk
-- DAC: SMSL m500
-- KEF R300
Did you connect a separate 5v power supply to iDefender when you tried? I had a similar problem with topping E30 and iDefender, which was resolved by using a power supply, contrary to what the idefender manual says.
 

AnalogSteph

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Missed this one -
Thanks - haven't come across this before. What root causes have you seen in these sort of cases?
Same as for any other ground loop, unbalanced connections between two devices that connect their audio ground to mains PE. Apparently the power supply currents couple into the PE conductor, so that there is an AC difference in ground level between both ends of the audio connection, which in turn is indistinguishable from a real signal.
 
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Dexter_prog

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Did you connect a separate 5v power supply to iDefender when you tried? I had a similar problem with topping E30 and iDefender, which was resolved by using a power supply, contrary to what the idefender manual says.

Yeah, while it does reduce the hum, it adds it's noise, a high-pitch hiss which is more annoying. So so far:
- When playing games: idefender with PSU
- when not playing: idefender with psu disconnected (AKA, no positive or negative effects, but keeps me from having to unplug my usb cable)
 

Evenor

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You need galvanic isolation to fix the problem and just decoupling the USB power is only a partial fix.
These works: https://hifimediy.com/product-category/usb-isolators/

I have the high speed version which you need for USB 2.0. It doesn't support the full USB 2.0 speed but works fine with most resolutions (I think it's limited to 32/384k and DSD 128 or DSD 64 so no 768k and 256 DSD). I used to use optical SPDIF before and it was more convenient.
 

asmoran

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Sorry to necro, but I'm having the exact same issue. Before I just go buy the isolator from the link above, would a power line conditioner with ground isolation also work? I'm looking at the furman PST-8D, specifically. I need to replace my old surge protector anyway, but don't want to keep buying the wrong thing (I have a useless iDefender now, too).
 

CtheArgie

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Yeah, while it does reduce the hum, it adds it's noise, a high-pitch hiss which is more annoying. So so far:
- When playing games: idefender with PSU
- when not playing: idefender with psu disconnected (AKA, no positive or negative effects, but keeps me from having to unplug my usb cable)
Important question, Bostero o Gayina?
 
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