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Is this a ground loop or equipment issue?

valsidalv

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I just purchased a KRK S8.4 subwoofer to use with my existing Audioengine A5+ speakers, connected to my PC via a USB DAC. The introduction of the subwoofer is causing noise issues and I'd appreciate some help in making sense of the current situation. All of my components are connected to a single power strip:
  • PC is a custom build with a 750 W power supply using a 3-prong plug
  • A5+ speakers have a built-in Class A/B amp (in the left one which powers the right) using a 2-prong plug
  • S8.4 subwoofer has a built-in Class D amp using a 3-prong plug with a ground lift switch
  • DAC is a small, relatively cheap NuForce uDAC-3 powered by USB
  • Power strip is 3-pronged, connected directly to the wall
  • My home is older and the electrical panel is probably due for an upgrade
The connection chain is: PC -- [USB] --> DAC -- [RCA] --> subwoofer -- [RCA] --> powered speaker -- [speaker wire] --> passive speaker. The subwoofer supports both balanced and unbalanced signals, whereas the speakers and DAC only have RCA. Here are the symptoms and my observations:
  • Without the subwoofer only a small static hum is emitted from the speakers at all times - barely noticeable, and definitely nothing to cry about
  • With the subwoofer there is a very loud static hum from the speakers and computer noise leaks through as well - completely unbearable
  • No combination of ground lift, polarity, or sensitivity switches on the subwoofer has any effect in lessening the noise
  • I bought an iFi iDefender+ to use with the DAC which quieted the static noise right up, except...
  • Anytime the DAC outputs sound, a loud whining noise goes with it until the DAC stops outputting. The noise is at a constant volume regardless of the DAC's volume control, and occurs at 1 kHz and all its multiples.
  • When I use my laptop on battery as the input to the DAC there are no issues
  • When my laptop is plugged into its 3-prong charger on the same power strip as the other components, I can hear the whine! It's not as loud as from my PC but still noticeable.
  • When my laptop is plugged into its charger on a different wall outlet, there is substantial static noise in addition to the whine
I hope that all makes sense. I was under the impression that ground loops cause an on-going static hum, which does not describe the whine. However, is some sort of ground issue affecting the DAC? I can't really pinpoint if I have a faulty/sensitive DAC or something else. I understand that balanced cables are probably the way to go, but that's an expensive endeavour in my case, requiring a new DAC and speakers. It may be worth it rather than trying all sorts of other things that may or may not work. I can also piecemeal these purchases by getting a new DAC first. Thanks in advance!
 

ZolaIII

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It's power transformer hum EMI getting in. Try to use a normal DAC with good EMI rejection rate, if it persists try using optical (SPDIF/Toslink) input to DAC.
 
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valsidalv

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That makes sense. Any recommendations for a DAC? I'm guessing I can safely go with anything that's recommended in the Review section of this site?
Also, might a power conditioner help in this case, if it can better isolate components? I know they aren't favoured here...
 

tonycollinet

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Whatever the noise source, it is almost certainly getting in via ground loop(s), of which I think you have multiple.

First thing I would do (AFTER swiching to Toslink from PC to DAC) is stop sending the RCA *through* the Sub. Get a splitter, and send separate RCA from the DAC to the Sub and speakers. This will reduce noise getting onto the RCA to Sub being passed on also to the speakers.

Aso - if you are getting a new DAC, strongly reccomend one with balanced output since your sub has balanced inputs, and this would go a long way towards eliminating loops introduced by the sub.
 
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ZolaIII

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For the purpose it doesn't have to be stellar performer (good 100+ THD+N and 2V unbalanced out) but with good optical lines input. I don't know what you want or consider convenient so go to index and look around. SBX G6 falls on my mind considering you already use PC but keep in mind it's EMI rejection isn't stellar (but it has optical I/O). See if your MB has a SPDIF out first.
 
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valsidalv

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The whole
Whatever the noise source, it is almost certainly getting in via ground loop(s), of which I think you have multiple.

First thing I would do (AFTER swiching to Toslink from PC to DAC) is stop sending the RCA *through* the Sub. Get a splitter, and send separate RCA from the DAC to the Sub and speakers. This will reduce noise getting onto the RCA to Sub being passed on also to the speakers.
The sub is meant to send output to the speakers. It has a built-in adjustable filter that keeps certain frequencies for itself and sends the rest to the speakers. If I bypass that feature I'll end up with messy bass.
 

ZolaIII

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For diagnostic purpose try to do what @tonycollinet suggested right now (if you have cables) using what ever integrated sound card you have on PC (using L and R + center and sub jack's).
 
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valsidalv

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For the purpose it doesn't have to be stellar performer (good 100+ THD+N and 2V unbalanced out) but with good optical lines input. I don't know what you want or consider convenient so go to index and look around. SBX G6 falls on my mind considering you already use PC but keep in mind it's EMI rejection isn't stellar (but it has optical I/O). See if your MB has a SPDIF out first.
Thanks. My motherboard doesn't have SPDIF but I'm not against buying a soundcard with it.
 
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valsidalv

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For diagnostic purpose try to do what @tonycollinet suggested right now (if you have cables) using what ever integrated sound card you have on PC (using L and R + center and sub jack's).
Fantastic idea, can't believe I didn't think of this earlier.
I used a 3.5mm to RCA cable and ran it from the motherboard's onboard soundcard to the subwoofer. There is quite a bit of static hum and it's really picking up on all sorts of computer noises. However, no high-pitched whine like I experienced with the DAC.
 

ZolaIII

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See if Asus Xonar SE fit's you (around 40$ [ALC1220]) or if you can find something cheaper which will do the yob done on desktop PC side.
Best regards and have a nice time.
 

tonycollinet

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The whole

The sub is meant to send output to the speakers. It has a built-in adjustable filter that keeps certain frequencies for itself and sends the rest to the speakers. If I bypass that feature I'll end up with messy bass.
Then even more important to think about a balanced connection to the sub - or at least eliminating the ground loop before the sub.
 

tonycollinet

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Here is where I think your ground loop is:

Screenshot 2022-02-17 at 10.37.40.png




Your speakers are not earthed, so I don't think there will be a loop there. If you can break the loop between PC and Sub eg via toslink, I think you'll be 90% there.

If you buy a new DAC, you don't want it to be grounded via the power supply or you may get another loop between the DAC and the sub. Then you'd definitely need a balanced connection.

You might get an improvement without further measures, by getting the swept area of the loop as small as possible. IE run the power cord for the sub closely along the RCA connection, past the DAC, and then along the USB wire, then along the PC Power lead. But you don't want that path to cross any (especially) monitor cables, or other wires from the PC. In fact separate as much as possible from other PC wires.

(Or this might just make things worse if the PC is the main noise source :)
 

AnalogSteph

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A little audio interface or DAC with balanced output is probably the way to go. Somewhere between $100-200, plus usually some TRS --> XLR (male) cables. Think either Topping D10BAL or Arturia Minifuse 1 / 2, Focusrite Scarlett Solo / 2i2, Tascam US-2x2HR, Audient iD4 MkII or MOTU M2. Maximum output is between +12 and +18 dBu for all of them.

If you're cheap and insist on using existing outputs, you can also run 3.5 mm / 2x RCA to 2x TS into a $25 Behringer HD400 and proceed with TRS to XLR from there. This route may be less effective though.
 

JayGilb

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Have you tried using a separate usb power supply into the side port of the iDefender+ ?
It is designed to be able to connect into the pc using the built in usb +5vdc from the pc or use a different usb power supply
plugged into the side of the iDefender+.
 
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valsidalv

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Then even more important to think about a balanced connection to the sub - or at least eliminating the ground loop before the sub.
Thanks for this and the diagram. Would the sub be causing a ground loop even if I have the ground lift switch turned on? It is equivalent to removing the grounding pin.
I will definitely have a fun time trying out your wiring suggestion - it's a mess back there o_O
 
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valsidalv

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A little audio interface or DAC with balanced output is probably the way to go. Somewhere between $100-200, plus usually some TRS --> XLR (male) cables. Think either Topping D10BAL or Arturia Minifuse 1 / 2, Focusrite Scarlett Solo / 2i2, Tascam US-2x2HR, Audient iD4 MkII or MOTU M2. Maximum output is between +12 and +18 dBu for all of them.

If you're cheap and insist on using existing outputs, you can also run 3.5 mm / 2x RCA to 2x TS into a $25 Behringer HD400 and proceed with TRS to XLR from there. This route may be less effective though.
I can definitely get another DAC and use balanced outputs to the sub (it has inputs for them). Where this exercise gets expensive for me is if I replace my speakers with ones that support balanced inputs, but I can get a DAC and see if that helps before tackling the speakers.
 
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valsidalv

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Have you tried using a separate usb power supply into the side port of the iDefender+ ?
It is designed to be able to connect into the pc using the built in usb +5vdc from the pc or use a different usb power supply
plugged into the side of the iDefender+.
Yes, that is how I'm using it and that's the only way it does anything for my setup. Without an external power supply the iDefender+ has no effect on the static noise.
 

tonycollinet

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Thanks for this and the diagram. Would the sub be causing a ground loop even if I have the ground lift switch turned on? It is equivalent to removing the grounding pin.
I will definitely have a fun time trying out your wiring suggestion - it's a mess back there o_O
Depends on exactly what the ground lift pin is doing. It's difficult to see how they could legally add a feature that disconnects the safety earth from the equipment. It may just be disconnecting the electronic circuit from the earth - in which case it is unlikely to eliminate the ground loop on an unbalanced connection.
 
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valsidalv

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Depends on exactly what the ground lift pin is doing. It's difficult to see how they could legally add a feature that disconnects the safety earth from the equipment. It may just be disconnecting the electronic circuit from the earth - in which case it is unlikely to eliminate the ground loop on an unbalanced connection.
I see. This is all it mentions in the manual about it:
[11] GROUND LIFT
Even the best studio environment can be subject to noise due to ground loops that can occur from the variety of
equipment that must be interconnected. Engaging the GROUND LIFT switch helps to reduce or eliminate this noise.
I have also just realized something - my iDefender+ is powering my DAC with an external power source that is connected to the power strip. So, there may in fact be another loop there as well. However, the iDefender+ does eliminate the static hum and feels a step closer to solving the problem.
So perhaps my best course of action is to get another DAC with USB and optical inputs, and RCA and balanced outputs. I can see if that new DAC takes care of the issue (using USB) and, if not, buy a sound card with an SPDIF out and use an optical connection. I can also try using balanced cables from the new DAC to the sub. If that makes sense, I have some very specific requirements for a DAC and some shopping to do.
 
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