• WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required as is 20 years of participation in forums (not all true). Come here to have fun, be ready to be teased and not take online life too seriously. We now measure and review equipment for free! Click here for details.

[Solved] Ground Loop Noise Identified. Balanced Connection Wanted. What Is the Best Solution for Me?

OP
S
Joined
Aug 7, 2019
Messages
52
Likes
21
Thread Starter #21
Have you tried using RCA to TRS unbalanced cables? The 308 MKII manual states that TRS should be used for connection to consumer kit...

INPUT PANEL
9. XLR INPUT – Connect professional equipment to this connector using a balanced XLR plug.
10. 6MM (¼") INPUT – Connect professional equipment to this connector using a 6mm (¼") balanced plug. Connect consumer equipment to this connector using a 6mm (¼") unbalanced plug.

From: https://adn.harmanpro.com/site_elem.../JBL_3_Series_MkII_Owners_Manual_original.pdf

This would be a relatively cheap thing to try vs. the isolator you link to.
That's a good suggestion in general. I have previously tried this and it didn't eliminate the ground loop. I just tried it again now, and it made the buzzing louder.
However, I used an RCA cable with an RCA to TS adapter. But I expect this will be the same result (ground loop) with an RCA to TS cable. If i'm wrong in thinking this, let me know.


I think I've decided to buy the Radial StageBug SB-6 since it does everything I want, is simple, relatively inexpensive, and I think measures well enough for my usage:
https://www.radialeng.com/product/stagebug-sb6/specifications (click graphs for AP measurements)
The alternative which may still have a ground loop problem is to buy a balanced DAC with all the features I want, then sell my D50s. But given the uncertainty and potential cost, i'd rather get an isolator.

Edit: SB-6 Isolator purchased. I'll reply with an update in 1-3 weeks when everything arrives.
 
Last edited:

Berwhale

Major Contributor
Forum Donor
Joined
Aug 29, 2019
Messages
1,757
Likes
1,980
Location
UK
#22
That's a good suggestion in general. I have previously tried this and it didn't eliminate the ground loop. I just tried it again now, and it made the buzzing louder.
However, I used an RCA cable with an RCA to TS adapter. But I expect this will be the same result (ground loop) with an RCA to TS cable. If i'm wrong in thinking this, let me know.


I think I've decided to buy the Radial StageBug SB-6 since it does everything I want, is simple, relatively inexpensive, and I think measures well enough for my usage:
https://www.radialeng.com/product/stagebug-sb6/specifications (click graphs for AP measurements)
The alternative which may still have a ground loop problem is to buy a balanced DAC with all the features I want, then sell my D50s. But given the uncertainty and potential cost, i'd rather get an isolator.
I hope the isolator works for you.
 

L5730

Addicted to Fun and Learning
Joined
Oct 6, 2018
Messages
542
Likes
314
Location
East of England
#23
This sounds a lot like the problem I was having.

PC (mains earth) > USB (+5v, D+/D-, GND) > D10 > RCA unbalanced cable > XLR pin 2 signal, pin 1+3 tied to ground/shield > Active Monitor Speakers (mains earth).
Got a low level buzzing only really obvious when I turned the speakers up beyond normal listening levels or shoved my ear right next to the driver.

For me, using a twin core + shield cable terminating cable shield and ground together to RCA ground and signal to the RCA pin. At the other end the signal is connected to XLR pin 2 (+/hot) and the ground cable is connected to pin 3 only. There is no ground connected to the XLR ground pin 1.
Adding a 100 ohm resistor to the RCA ground end (as advised by another member here) would balance impedance with the output impedance of the D10 signal connection - but I didn't bother.

I am running a pair of 4 meter cables, with a bit of it coiled (naughty!) sat on top of the PC case and hanging right over a mains 4-gang extension lead, behind a router and modem... it's a filthy place but I get no noise at all. YMMV.

Other options are:

Optical output from PC, as Amir said. Optical has no metal cable connection and no ground connection. Proper isolation.

USB isolators (ADuM chip based) which may or may not have sufficient DC-DC transformers to provide enough power for the D50 from the original USB port - but it does have an external power input so likely not a problem. The downside, even if you got a well designed and well made one based on an ADuM chip, is that it will only do 24 bit 96 kHz at best. They simply cannot handle the speed of full USB 2.0 two-way traffic!
For example: https://hifimediy.com/usb-isolator
Isolators based on a Silanna chip do handle high frequency audio and allow the proper full USB 2.0 data speed or more perhaps - but they ain't cheap. I've seen some use a proprietary FPGA setup.

iFi iDefender 3.0 :- A cleaver little circuit with an additional input for external +5v power. When an external PSU is added it intelligently cuts the ground connection between the device and PC. It operates at full USB 3.0 speeds, but is not an isolator, more a ground loop breaker.

Any of the methods involving shoving something in the USB connection would probably solve a ground loop issue but would likely cause some noise at 8 kHz. This is the noise from the actual data transmission timing or something or other. 'Spectrum spreading' or a term like that used in more complicated devices (like with the FPGA) could reduce this data noise.

Transformers in the audio path. I didn't like the idea of shoving something in the audio path. It's just a pair of coils and the alternating current in the audio signal (that's what it is) induces a current across a gap in another coil. Seems like a lot of potential losses in frequency response. Fine for in the car, but not at home. It's funny, but this is actually how the USB isolators work too - it's just that the coils are ridiculously thin and small and the data connection is two-way and timing is very critical to the transmission working or not.

Doing a dodgy test job or carving up a USB cable, breaking the shield and ground connections and seeing what happens. I had to connect the ground to begin with, or at least have a common ground between PC and DAC somewhere else the USB connection would not establish. Once established the ground can be severed, except for when sample rate is changed. However, DO NOT DO THIS for a long term solution beyond testing. If the Data lines fall too far beyond a certain voltage difference to the common USB ground, the USB chips could be damaged in the DAC or the PC motherboard.


Product designers could build in a solution, which would be AFTER the USB chip (XMOS) but before the DAC (ESS) chip. As the USB data is two way, it is a trouble isolating that. But the digital audio signal from the USB chip could be sent across a fast isolator. It could increase jitter (timing errors in the data) but would allow for full separating of USB ground from DAC ground. Singxer make something like this, with IIS outputs.

If you use a laptop (on battery or powered by double-insulated DC PSU (no mains)) then you won't have a ground loop and won't have an issue. The Raspberry Pi is fine in this regard. However, connect a TV set via HDMI and back comes some noise, actually a lot of nasty noise! The TV is mains earthed.

I suppose you could look into star grounding and that whole load of fun!
My little list of things to handle should I win the lottery and have a house built gets longer and longer...
 
OP
S
Joined
Aug 7, 2019
Messages
52
Likes
21
Thread Starter #24
Thanks for your input. Hopefully it helps someone else with a similar issue.

Optical output from PC, as Amir said. Optical has no metal cable connection and no ground connection. Proper isolation.

Transformers in the audio path. I didn't like the idea of shoving something in the audio path. It's just a pair of coils and the alternating current in the audio signal (that's what it is) induces a current across a gap in another coil. Seems like a lot of potential losses in frequency response. Fine for in the car, but not at home. It's funny, but this is actually how the USB isolators work too - it's just that the coils are ridiculously thin and small and the data connection is two-way and timing is very critical to the transmission working or not.
I tried optical and posted results right after Amir. It didn't really help in my situation due to ground loop noise mostly coming from the USB power cable going in to the D50s.

As for shoving a transformer in the audio path, I would agree with what you said if it was a low quality one. However, the SB-6 I purchased and am waiting to arrive seems to measure well: https://www.radialeng.com/product/stagebug-sb6/specifications . None of the other isolation transformers I found in this price range or lower had AP measurements published by the manufacturer (didn't look elsewhere). So I can see the uncertainty in how it would affect your audio.

The other reason for me deciding to get an isolation transformer is to convert unbalanced to balanced without having to change my DAC or preamp. I needed cables over 15ft for better positioning, so I figured it was best to go balanced.
 

g29

Addicted to Fun and Learning
Joined
May 1, 2019
Messages
520
Likes
310
#25
....
I tried optical and posted results right after Amir. It didn't really help in my situation due to ground loop noise mostly coming from the USB power cable going in to the D50s.
....
Why not try a USB ground block cable ???
 

majingotan

Addicted to Fun and Learning
Forum Donor
Joined
Feb 13, 2018
Messages
932
Likes
967
Location
Laguna, Philippines
#26
I tried optical and posted results right after Amir. It didn't really help in my situation due to ground loop noise mostly coming from the USB power cable going in to the D50s.
Can't you just remove the USB cable? That should completely isolate your D50s from USB mains noise save you all of the headaches
 
OP
S
Joined
Aug 7, 2019
Messages
52
Likes
21
Thread Starter #27
Why not try a USB ground block cable ???
I don't know what a USB ground block cable is, nor was it previously suggested. Otherwise I would have considered it. Care to explain or provide a link?

Can't you just remove the USB cable? That should completely isolate your D50s from USB mains noise save you all of the headaches
I did remove the USB data cable, and that was the result. As for saving me the headaches, I think I've already done that with the isolator I've purchased (waiting for it to arrive).


I'm gonna mark this thread as solved for now.
 

majingotan

Addicted to Fun and Learning
Forum Donor
Joined
Feb 13, 2018
Messages
932
Likes
967
Location
Laguna, Philippines
#28
I did remove the USB data cable, and that was the result.
Not just the data, the whole cable itself including the 5V power from the USB, literally zero USB cable.
 
OP
S
Joined
Aug 7, 2019
Messages
52
Likes
21
Thread Starter #29
Not just the data, the whole cable itself including the 5V power from the USB, literally zero USB cable.
That produces zero noise. But also zero music as you would expect with the D50s not having any power. Also, earlier in the thread I tried to battery power the D50s, and that removed the noise from that source. But that wasn't an ideal solution for me.
 

g29

Addicted to Fun and Learning
Joined
May 1, 2019
Messages
520
Likes
310
#30
I don't know what a USB ground block cable, nor was it previously suggested. Otherwise I would have considered it. Care to explain or provide a link?
....
I don't have a D50, but it looks like it has it's own +5VDC power supply. If it doesn't need +5VDC power from the PC, you can take a USB cable and disable the power ground and power +5VDC lines and break the shield ground. This will just send the +/- data signal to the DAC, thus isolating the ground from the PC.

If it needs the power ground and +5VDC, you can splice 2 cables together to get power ground and +5VDC from a USB phone charger and break the shield ground, again isolating the ground from the PC.

Some companies make similar items from $50 to $500 that claim to do more than just break the ground loop, but you can make a USB ground loop block from spare parts.

DIY ground block cable post


 
Last edited:
OP
S
Joined
Aug 7, 2019
Messages
52
Likes
21
Thread Starter #31
I don't have a D50, but it looks like it has it's own +5VDC power supply. If it doesn't need power, you can take a USB cable and disable the power ground and power +5VDC lines and break the shield ground. This will just send the +/- signal to the DAC, thus isolating it from the PC.

If it needs the power ground and +5VDC, you can splice 2 cables together to get power ground and +5VDC from a USB phone charger, again isolating it from the PC. Some companies make similar items from $50 to $500, but you can make one from spare parts.
That makes far more sense now. I must have forgot your previous post because I didn't understand what a ground block cable was (and google didn't help).

I think i'll give the DIY cable a try later and see if it works in combination with battery powering the D50s (Edit: If I already have spare cables somewhere). If I do, i'll post the results here.

But I'll most likely end up sticking with the isolation transformer solution because I need 20ft+ cables and assume balanced is the way to go in that case.
 

majingotan

Addicted to Fun and Learning
Forum Donor
Joined
Feb 13, 2018
Messages
932
Likes
967
Location
Laguna, Philippines
#32
That produces zero noise. But also zero music as you would expect with the D50s not having any power. Also, earlier in the thread I tried to battery power the D50s, and that removed the noise from that source. But that wasn't an ideal solution for me.
I see. This is all you need for zero noise: a cell phone charger to 5V port + optical from computer:

IMG_1699.JPG
 
OP
S
Joined
Aug 7, 2019
Messages
52
Likes
21
Thread Starter #33
I see. This is all you need for zero noise: a cell phone charger to 5V port + optical from computer:
Yes, that would probably work, and I sort of mentioned it earlier in the thread:
I tried using my USB battery to power the D50s, and that seems to have eliminated the noise that was coming from the power cable which was the main source. The noise from the USB data cable remained, and of course that could removed with optical.
While that might be a good solution for some people, I don't think it was best for me. But definitely something for other people reading this to consider.
 

g29

Addicted to Fun and Learning
Joined
May 1, 2019
Messages
520
Likes
310
#34
That makes far more sense now. I must have forgot your previous post because I didn't understand what a ground block cable was (and google didn't help).

I think i'll give the DIY cable a try later and see if it works in combination with battery powering the D50s (Edit: If I already have spare cables somewhere). If I do, i'll post the results here.

But I'll most likely end up sticking with the isolation transformer solution because I need 20ft+ cables and assume balanced is the way to go in that case.
I think you will still be driving 20 feet with RCA 2V with the transformers. Your DAC isn't going to output XLR 4V via the RCA 2V outputs. That being said, 20 feet is a long USB run as well.
 
Last edited:
OP
S
Joined
Aug 7, 2019
Messages
52
Likes
21
Thread Starter #35
I think you will still be driving 20 feet with RCA 2V with the transformers. Your DAC isn't going to output XLR 4V via the RCA outputs. That being said, 20 feet is a long USB run as well.
The USB cables don't need to be 20ft in my case, and if they did, that can be dealt with easily. The ones that came with my D50s are just long enough.

From what I was told by Radial and from the product page, the SB-6 will convert unbalanced to balanced in my situation. And the SB-6 is a unity gain device, so it will remain 2V (afaik). From my understanding, this is fine for my active speakers. Edit: On the output of the SB-6, i'll be using TRS to XLR cables to my subwoofer. Then from my subwoofer, it will be XLR to the monitors. Edit2: I think the JDS Atom can output ~8.6Vrms on high gain through the RCA out in case I needed that, though it says to use low gain the manual. However, the SB-6 will perform better with a lower Vrms according to the AP measurments.
 
Last edited:

L5730

Addicted to Fun and Learning
Joined
Oct 6, 2018
Messages
542
Likes
314
Location
East of England
#36
Re. Ground Block cable.

If I read the suggestion correctly, the poster is suggesting removing the +5v power and ground connections but keeping the Data + and Data - lines.
This is not a good idea. Removing the power +5v is fine but really there should be a USB ground connected when the Data lines are connected as the Data lines are referenced to that USB ground. As I mentioned, if the Data lines stray too far out of voltage difference to the USB ground, it could result in damage.
The ifi iDefender product is more complicated than simply severing the USB ground and power. It does it intelligently and more safely - but I don't know quite how.

As for Optical from the PC to the DAC, I was assuming you were powering the DAC from an external DC PSU with no mains ground connection (double insulated wall wart). Most phone chargers (+5v and enough Amperes) would do exactly that. It's rather like using a +5v battery pack to power the DAC - neither have a mains connected ground ;)

The in-line audio isolator Radial SB-6 will solve the ground loop issue, unless the issue is manifesting somewhere else. That's a given.
It looses 2 dB and raises the output impedance to 600 ohm. You'll want to engage the ground lift button, else it'll probably still hum/buzz.

For the JDS Atom, low gain is preferred as it has higher headroom on the input. As long as you don't exceed the input level specs, then you could run hi-gain.
 

Severian

Active Member
Forum Donor
Joined
Jan 11, 2019
Messages
186
Likes
158
#37
The iFi iDefender has worked for me with the three USB devices I've tested it with, all of which were unbearably noisy when connected directly to my desktop PC and outputting via unbalanced RCA: a Schiit Modi 3, a Pioneer DDJ-1000, and most recently a MOTU M4.

The quietest any of those three devices got was when I had the Modi 3 connected via optical, but for some unknown reason the optical out on my motherboard died and the other two devices don't offer optical input anyway.
 
OP
S
Joined
Aug 7, 2019
Messages
52
Likes
21
Thread Starter #38
If I read the suggestion correctly, the poster is suggesting removing the +5v power and ground connections but keeping the Data + and Data - lines.
This is not a good idea. Removing the power +5v is fine but really there should be a USB ground connected when the Data lines are connected as the Data lines are referenced to that USB ground. As I mentioned, if the Data lines stray too far out of voltage difference to the USB ground, it could result in damage.
The ifi iDefender product is more complicated than simply severing the USB ground and power. It does it intelligently and more safely - but I don't know quite how.

For the JDS Atom, low gain is preferred as it has higher headroom on the input. As long as you don't exceed the input level specs, then you could run hi-gain.
Thanks for saving me from potential damage. I'll probably avoid any DIY options given the uncertainty about their safety, such as the previously suggested removal of the ground from my speakers which would be unsafe.

The ifi defender seems like the best option besides toslink if I didn't need/want a balanced connection.

About the Atom, I was referring to the RCA output with high gain, not the input. My input (D50s) should be under 2.1Vrms as recommended in the manual. So using high gain is not a problem. I was suggesting to use high gain to boost the RCA output if needed since the headphone and RCA output are the same for the Atom afaik.
 

g29

Addicted to Fun and Learning
Joined
May 1, 2019
Messages
520
Likes
310
#39
Re. Ground Block cable.

If I read the suggestion correctly, the poster is suggesting removing the +5v power and ground connections but keeping the Data + and Data - lines.
This is not a good idea. Removing the power +5v is fine but really there should be a USB ground connected when the Data lines are connected as the Data lines are referenced to that USB ground. As I mentioned, if the Data lines stray too far out of voltage difference to the USB ground, it could result in damage.
.
The DAC is already grounded on the RCA side, thus causing the ground loop. Are 3 separate grounds (power, shield and RCA) ALL actually necessary ???
 
Last edited:

L5730

Addicted to Fun and Learning
Joined
Oct 6, 2018
Messages
542
Likes
314
Location
East of England
#40
The DAC is already grounded on the RCA side, thus causing the ground loop.
That is true, and it's unlikely that the potential (voltage) difference between the USB ground on the PC and the USB ground on the DAC would become significantly different for the Data lines to be too far outside of their normal operating voltage reference to those ground(s).
However, it's a bit risky.

I haven't tried the ifi Defender myself, but I looked hard at how it's implementation could work and it seems a safer way to go. I believe that if the ground of either end of the USB connection because too different from the other, it would reconnect or shut off.

@SoBu yes, don't go around taking off mains earth pins from equipment. If it has one, it's for a good reason. If you aren't entirely certain of what you are doing then it's potentially lethal if something goes wrong. No intent to scare monger, just to point out to exercise caution.
 
Top Bottom