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Audiophile PC ground loop issues?

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yavormoskov

yavormoskov

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Do you remember when @amirm reviewed KTB and measured 109.6 and 109.3 dB SINAD. And the official specs stated 120 dB. I guess it was because of the USB bus noise, interferance and/or ground issues. I just took a leap of fate - bought Intona USB 3.0 Isolator. And the isolator is friendly with XMOS. There was one in open box condition on Ebay, heavily discounted from brand new price, so in a week my grounding issues between the amp powered by Molex and the KTB powered by USB should be resolved completely (I hope). Many thanks to @KSTR for telling me about this German company.


intona.JPG
 

Novak

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My 2 cents,
Maybe that is too late but I am happy to share my cheap solution (which has no impact on SQ). I connect a simple wire :
- from my amp earth connector, to earth of my multiplug.
- or I connect a wire between the earth connector of my streamer and my Dac.

As said above, the most important is to break the loop. I would not buy a specific équipement except this one: Groundhog+
 
OP
yavormoskov

yavormoskov

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My 2 cents,
Maybe that is too late but I am happy to share my cheap solution (which has no impact on SQ). I connect a simple wire :
- from my amp earth connector, to earth of my multiplug.
- or I connect a wire between the earth connector of my streamer and my Dac.

As said above, the most important is to break the loop. I would not buy a specific équipement except this one: Groundhog+
Already solved it. Bought Intona USB 3.0 isolator and no more grounding issues. Motherboard USB 2.0 header adapter to Intona USB 3.0 isolator to Khadas tone boards. Yes, it is not a cheap solution but it works without a hitch.
 

g29

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Yes this is a classic "ground loop" example.
The root problem is that the ground voltages at the DAC and at the amp are not the same (the difference is the noise) but are connected together tightly in the PC's power supply. This voltage difference is applied to your unbalanced interconnect cable where it forces a heavy current through the shield and that's where the noise is actually created as an audio signal. With better cables (low shield resistance) the noise is less, but won't go away.

You have to "break the loop" literally, unless all the supply voltages and the ground they are referenced to come from one single point.
This can be done in several ways:
1) Insert audio isolation transformers in the connection from DAC to Amp. Might be not an audiophile solution unless expensive transformers are used (Lundahl, Jensen, CineMag, Sowter, ...) and choice of model is critical.
2) Insert an USB Isolator that has enough power to supply the Khadas. Intona's USB Isolator might work well and is reasonably priced though not exactly cheap (I use it on a daily basis but haven't tried bus-powering anything from it, specs say it is good for at least 300mA).

3) Somewhat cheating, but still might work good enough at very low cost:
- Use the best and shortest(!) audio cables between DAC and amp, and add an additional thick(!) ground balancing wire that attaches to the (audio) grounds of these two devices. We want to make the resistance of this ground path as low as possible.
- Use the longest and cheapest USB cable in an effort to make this (parasitic) ground path high resistance (relatively speaking) so that it does not dominate. And it is a very good idea to wind up the cable as a coil, preferably on a large ferrite toroid core, or on a laminated core salvaged from an old toroid power transformer.
We want the noise voltage to be dropped along this path, not along the audio signal path.

What about using 3 USB2 PCB terminals to separate power and signal and break the shield and power ground continuity between the PC and the DAC ?

I get hum with the KTBD if I use only the USB from the PC for signal and power (without a USB isolator). If I use S/PDIF from the PC for signal and USB power from a wall wart charger, no hum (but am sample rate limited by the soundcard). I am assuming the same might be accomplished by doing similar with the modified USB connection to break the power ground and the shield ground between the PC and the KTBD. It would be a lot cheaper than "audiophile" products and you could supply your own 5VDC sufficient to drive the KTBD.
 

g29

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No more KTBD hum.

FWIW, I made a USB2 Y-cable tonight to separate the souce of the data and power and break the shield and ground. I used 2 spare USB2 cables I had on hand using a 12" USB2 Male/Female Type-A extension cable for data and a USB2 male Type-A/B patch cable for +5VDC power.

I cut the male B end off of the male A/B cable to carry +5VDC power (disabling data lines). I then spliced it into the Male/Female extension cable's power lines, cutting off the PC's USB +5VDC power and breaking the ground and shield between the PC and the KTBD.

I plugged the male/female A extension cable into the PC to pass data only and the A power cable into a USB phone charger to power the KTBD. The KTBD was then plugged into the female A socket of the Y cable.

No more hum on the KTBD for the grand total cost of a few spare parts from the junk box. No moat and no bridge was required.

I noticed the A/B cable's power lines were a heavier gauge wire than the extension cable. I may try to find a different extension cable that has 20 gauge power lines and make a new Y-cable with the same gauge power wires.
 
Last edited:

CostasD

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My 2 cents,
Maybe that is too late but I am happy to share my cheap solution (which has no impact on SQ). I connect a simple wire :
- from my amp earth connector, to earth of my multiplug.
- or I connect a wire between the earth connector of my streamer and my Dac.

As said above, the most important is to break the loop. I would not buy a specific équipement except this one: Groundhog+
Could you please explain it more clear?

My connection path is PC->USB DAC->RCA->Powered Monitors
 
Last edited:

CostasD

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No more KTBD hum.

FWIW, I made a USB2 Y-cable tonight to separate the souce of the data and power and break the shield and ground. I used 2 spare USB2 cables I had on hand using a 12" USB2 Male/Female Type-A extension cable for data and a USB2 male Type-A/B patch cable for +5VDC power.

I cut the male B end off of the male A/B cable to carry +5VDC power (disabling data lines). I then spliced it into the Male/Female extension cable's power lines, cutting off the PC's USB +5VDC power and breaking the ground and shield between the PC and the KTBD.

I plugged the male/female A extension cable into the PC to pass data only and the A power cable into a USB phone charger to power the KTBD. The KTBD was then plugged into the female A socket of the Y cable.

No more hum on the KTBD for the grand total cost of a few spare parts from the junk box. No moat and no bridge was required.

I noticed the A/B cable's power lines were a heavier gauge wire than the extension cable. I may try to find a different extension cable that has 20 gauge power lines and make a new Y-cable with the same gauge power wires.
Could you make some sort of a diagram? It's not clear what your connections are
 

AnalogSteph

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My connection path is PC->USB DAC->RCA->Powered Monitors
Which model powered monitors? Sounds like an absolute classic scenario for a ground loop in any case. If the monitors have balanced inputs as well, I would suggest the classic "care package" of a Behringer HD400 plus cabling (2 pcs. RCA --> 1/4" TRS plus 2 pcs. 1/4" TRS --> XLR male or 1/4" TRS --> 1/4" TRS if there's no XLR available).

Oh, and please consider opening a thread of your own in the newbie section instead of resurrecting a 3-year-old one. Preferably with information where you are located, so people can suggest things you can actually buy and matching retailers.
 
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