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darth vader

Annoying earth hum issue using USB

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I'm getting an annoying earth hum (or at leat thats what I think it is going by the sound) using USB hook up between my fruit computer (2014 imac) and a Line Magnetic DAC.

 

The background is I have been using a 5m optical connection with no issues. A friend visited with his laptop with some fancy software. After loading the DAC driver we had a bit of listening and discussion on the merits of optical and USB. I've been wanting to try USB for some time. I had tried it before but had difficulties overcoming getting signal out of fruit computer via USB. After much googling I finally got it worked out.

I managed to scrounge up an extension USB cord, and thought I was in business. I could now finally enjoy the rumoured improvements over optical.

 

But alas, I couldn't resolve the hum that I was getting. 

I disconnected all other USB devices, save the drive where my music files are...no change.

I moved the computer to a point where I could eliminate the USB extension and use the same USB cable that was working fine a few hrs before on Martys laptop...again, no change

 

 

So, I'm at a bit of a loss for things to try. Apart from jerry rigging some kind of earth lead from the DAC to the PC, I can't think of anything. Besides, I've never seen nor heard of that ever being a fix. Even if it was a fix, I dont think I'd like to have to live with that. Just not the right thing it feels. 

 

Anybody got any idea what might be the cause and possibly a remedy?

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Some may argue that going from optical to USB is a step back not an improvement, but let's leave this aside. USB should work without hum, THEN we may try to determine the superiority of one connection way over another.

 

Sounds like what you are experiencing is a classic ground loop. What it is and why I leave to the powers of Google, more importantly let's look how to fix it. In principle what you need to do is break the ground circuit to stop the current flow. There are several ways to do this. You can:

- get an USB isolator (cheap but usually limited to 48k)

- get some sort of USB "enhancer" like Audioquest Jitterbug, Schiit Wyrd etc (some are quite expensive)

- get a USB cable that allows to plug in a separate power source (note that the alternate power source may have the same issue)

- power your imac and the dac from the same powerboard (I sometimes see this recommended, but never worked for me. Its free to try though)

- get a power cable with no earth prong for one of the devices (and risk being electrocuted)

There may be more ways. I'm not familiar with your DAC model, but some DACs have a jumper labelled "ground lift" or something equivalent.

 

 

 

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Thanks @PleasantSounds

 

I will try using the same power board, this makes some simple sense.

 

I'll look into weather or not my DAC has "ground lift" (LM-502CA)

 

These are both free to try and that is important to me on the grounds that optical is working just fine. If USB is better, it should be so for free.

 

An USB isolator sounds like it could possibly do the trick, but if its at an additional cost then that to me is possibly a case for dismissing USB's supposed superiority, even if it does work

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7 hours ago, PleasantSounds said:

Some may argue that going from optical to USB is a step back not an improvement, but let's leave this aside. USB should work without hum, THEN we may try to determine the superiority of one connection way over another.

Just going on my own personal experience where in direct comparison I’ve heard Audirvana connected with USB sounding a lot closer in quality to what I’ve achieved on my windows laptop than what was heard from Darths imac with optical.

Obviously other differing factors may make a difference like my original comparison with Audirvana was with a mac mini not an imac but nonetheless the drop in sound quality with the iMac connected via optical meant it’s worth trying USB to see what improvements are possible.

 

I should also add that my previous experiences with optical have been less than stellar too though not saying it’s not possible to get a good result with optical.

 

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8 hours ago, darth vader said:

 

An USB isolator sounds like it could possibly do the trick, but if its at an additional cost then that to me is possibly a case for dismissing USB's supposed superiority, even if it does work

 Actually not that big an outlay to try.

 

https://addictedtoaudio.com.au/products/audio-quest-jitterbug-usb-data-power-noise-filter?variant=16064026755&gclid=EAIaIQobChMIuPCI_Pj61gIVRpVoCh26LQzlEAQYASABEgJOofD_BwE

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18 hours ago, Martykt said:

Just going on my own personal experience where in direct comparison I’ve heard Audirvana connected with USB sounding a lot closer in quality to what I’ve achieved on my windows laptop than what was heard from Darths imac with optical.

 

 

To be fair, my music files are mostly FLAC, not WAV. This came about more by chance than good planning.

I think I have to try USB and give it a fighting chance before I comment on its better or worse than optical status. Once I work out which works better for me, then I can start playing with file types.

 

That link you gave might be a solution. I'd still like to understand what the cause is.

It didn't happen on your laptop, but does on my computer. Stands to reason the problem is with my computer.

Perhaps it has something to do with the metal case on an imac?

Yet to try same powerboard and possible ground lift on dac.

 

 

@Zaphod Beeblebrox I dont get any hum issues in my system and not when using optical. I'm trying to fathom how an RCA hum eliminator would be of help for what seems to be a USB issue? I could be missing your message here.

 

 

Edited by darth vader

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I'm assuming that any connection in the system could be involved in a loop. USB has to be involved - a loop by definition has more than one link involved. That's why I posed it as a question.

 

It seems to me that any loop causing a hum has to involve the analogue signal path and so an RCA hum eliminator seems a sensible bet to fix it!

 

It's worth adding, the iMac is necessarily mains powered and the laptop may not have been. That's a point to look into - try a different power lead in case of an issue there.

 

 

 

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It's quite likely that the USB connection closes the circuit which extends all the way to the amp - therefore the RCA circuit breaker may indeed do the trick.

On the other hand the DAC also has an analog part of the circuit , so it could be affected even if the loop is just between the imac and the DAC (I'm not 100% sure on this one).

Also worth trying is a USB cable with ferrite choke.

 

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That rca isolator is most likely transformer isolation, so you will lose sound quality. Try just lifting the shield from the rca connections.

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On 18/10/2017 at 10:12 PM, darth vader said:

or at leat thats what I think it is going by the sound

Unlikey to be "earth" ... hence some of the help youre getting unlikely to be vaid.

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On 18/10/2017 at 10:12 PM, darth vader said:

I'm getting an annoying earth hum (or at leat thats what I think it is going by the sound) using USB hook up between my fruit computer (2014 imac) and a Line Magnetic DAC.

 

The background is I have been using a 5m optical connection with no issues. A friend visited with his laptop with some fancy software. After loading the DAC driver we had a bit of listening and discussion on the merits of optical and USB. I've been wanting to try USB for some time. I had tried it before but had difficulties overcoming getting signal out of fruit computer via USB. After much googling I finally got it worked out.

I managed to scrounge up an extension USB cord, and thought I was in business. I could now finally enjoy the rumoured improvements over optical.

 

But alas, I couldn't resolve the hum that I was getting. 

I disconnected all other USB devices, save the drive where my music files are...no change.

I moved the computer to a point where I could eliminate the USB extension and use the same USB cable that was working fine a few hrs before on Martys laptop...again, no change

 

 

So, I'm at a bit of a loss for things to try. Apart from jerry rigging some kind of earth lead from the DAC to the PC, I can't think of anything. Besides, I've never seen nor heard of that ever being a fix. Even if it was a fix, I dont think I'd like to have to live with that. Just not the right thing it feels. 

 

Anybody got any idea what might be the cause and possibly a remedy?

Sure fix is to isolate the "source end" of the system from the "power Amplifier" end.

 

Use a small isolation transformer to power the PC, any monitor plugged into the PC and anything else like a DAC (although the DAC would have it's own isolation via a linear transformer based power supply) that is forms part of the source end of the system. 99.9% of PC's have a switchmode supply, this is why you had success with optical, bit not with a cable with shield connected ground, aka USB cable.

Thing is, at the switchboard, the Earth is connected to the Neutral, this is the path of the ground loop, Earth and ground are separate things in some cases and shouldn't be mixed up.

 

I recently fixed a hum that was caused by a ground loop via the VGA connection, which coincidentally forms part of the PC front end of my system. The Isolation transformer I employ was connected to the DAC, the PC, but not the monitor. Subsequent connection to the transformer and voila, dead silence and a fantastic listening session.

 

Switch mode power supplies do not have isolation through them from the input to the output, unlike a linear power supply with a transformer and will cause a ground loop in the single ended system, weather or not it is detectable or not, via the speakers output.

The Isolation Transformer will break the Neutral to Earth connection, but maintain the protective chassis earth. Correct earth fault protection on the output of the Isolation Transformer should employ a 2 pole device called an RCBO, which is the same device used in caravans and similar "floating" earth type installations, this is a Legislative Requirement BTW

 

Best of luck, but IMHO if you use a PC and you want to go with RCA Line out  USB or SPDIF an Isolation Transformer will become part of the hardware within your system and a valuable tool to detect ground loops and fix them.

 

Edited by Guest
tidy up spelling, this IS the Gound Loop Breaker in a nutshell

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On 2/12/2018 at 10:45 AM, 125dBmonster said:

Switch mode power supplies do not have isolation through them from the input to the output, unlike a linear power supply with a transformer and will cause a ground loop in the single ended system, weather or not it is detectable or not, via the speakers output.

Good info; did not know that about SMPS vs LPS.   Thanks Monster, good details in your post.

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On 2/12/2018 at 9:45 AM, 125dBmonster said:

Switch mode power supplies do not have isolation through them from the input to the output, unlike a linear power supply with a transformer and will cause a ground loop in the single ended system, weather or not it is detectable or not, via the speakers output.

Switched mode power supplies in Australia could use two transformers, one to step down the 50Hz mains voltage, and then another operating at a high audio or an ultrasonic frequency in switched mode.  If the audio device takes its power from the output of the second transformer there would be two degrees of isolation.  This is just one approach for a switched mode power supply.

 

Which particular piece of audio equipment for use in Australia are you aware of that is designed to provide power to the electronics and to an audio socket for the electronics, without isolation from the mains? 

 

Are you suggesting that an audio socket would have its chassis/ground side connected to the neutral of the mains power?  That would seem a dangerous, if not illegal, approach.

Edited by MLXXX

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8 minutes ago, MLXXX said:

Are you suggesting that an audio socket would have its chassis/ground side connected to the neutral of the mains power?  That would seem a dangerous, if not illegal, approach.

Firstly, what is an audio socket ?

Secondly I literally have no idea what you are talking about and just possibly skimmed a little my above post.

 

Please also study the Mutiple Earthed Neutral, before even slightly suggestion of anything dangerous from my suggestions, geez, WTFAY ?.

http://www.electricalaxis.com/2016/10/what-is-multiple-earthed-neutral.html

13 minutes ago, MLXXX said:

Which particular piece of audio equipment for use in Australia are you aware of that is designed to provide power to the electronics and to an audio socket for the electronics, without isolation from the mains?

I have literally no idea what you are talking about again sorry "designed to provide power to electronics and WTF is an audio socket could mean anything, without isolation

 

My apologies Mate I don't understand non Electrical Engineer/Electrician speak

 

And please, before shooting from the hip a bit, please do some reading about what a switchmode driver is, and how it works

Please also read about how a Linear Transformer supply works as well

 

Then maybe I'll have a go at answering an intelligent question

 

I literally have no idea why you made that post other than to fill time in your day.

 

 

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38 minutes ago, 125dBmonster said:

Firstly, what is an audio socket ?

On a pc, it would include a 3.5mm headphone socket, or microphone socket.  On other equipment it could include an RCA socket or an XLR socket. 

 

Irrespective of the power supply type, linear or switched mode, there should be isolation from the mains for Australian equipment that allows a user to plug into an audio socket, whether it is RCA, DIN,  or any other kind of audio socket, without exposing a user to potential hazardous voltages.

 

There appears to have been confusion of some kind. I took these words of yours literally:

 

On 2/12/2018 at 9:45 AM, 125dBmonster said:

Switch mode power supplies do not have isolation through them from the input to the output, unlike a linear power supply with a transformer and will cause a ground loop in the single ended system, weather or not it is detectable or not, via the speakers output.

The Isolation Transformer will break the Neutral to Earth connection,

Those words suggest that using a switched mode power supply would result in the  audio equipment electronics, and any associated audio socket including a speaker output socket, being connected to the neutral of the mains.  I am not aware of any approval for such circuitry in Australia. It would indeed present a potential hazard.

Edited by MLXXX

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12 minutes ago, MLXXX said:

Those words suggest that using a switched mode power supply would result in the  audio equipment electronics, and any associated audio socket including a speaker output socket, being connected to the neutral of the mains. 

Get a multi meter out switch it to continuity and see for yourself, neutral on the input pin of the mains  plug to the output ground of the RCA, headphone, whatever and find out for yourself, please.

You will be isolated via a Linear Transformer, but not via the switchmode driver.

 

 

BEFORE ANYTHING ELSE< UNPLUG THE DEVICE FROM THE MAINS AND LEAVE IT 10 minuets before doing any testing 

Edited by Guest

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22 minutes ago, MLXXX said:

It would indeed present a potential hazard.

If you can please explain this circuit in detail please, curious.

 

please do not open, build or meddle with any audio equipment internals 

Edited by Guest
bit harsh, meant to be fun

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14 minutes ago, 125dBmonster said:

If you can please explain this circuit in detail please, curious.

 

please do not open, build or meddle with any audio equipment internals as I feel you may be the potential hazard

It is a long-standing practice in Australia not to rely on the electrician to have wired the active and neutral the correct way around.  One in a thousand old power sockets could be wired with the active and neutral interchanged, and that could go undetected for decades.  If circuitry were permitted in Australia as you have described it, then the chassis of the equipment could float at mains potential and a user touching an audio socket connected to the chassis could receive a fatal electric shock if they were in some other way connected to earth. 

 

As for your second remark, it is condescending and inappropriate, though I guess you have no knowledge of my background.

Edited by MLXXX

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18 minutes ago, 125dBmonster said:

Get a multi meter out switch it to continuity and see for yourself, neutral on the input pin of the mains  plug to the output ground of the RCA, headphone, whatever and find out for yourself, please.

I have no equipment that provides continuity between the mains cord neutral pin and and the chassis side of an audio socket of the equipment.

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11 minutes ago, MLXXX said:

It is a long-standing practice in Australia not to rely on the electrician to have wired the active and neutral the correct way around.  One in a thousand old power sockets could be wired with the active and neutral interchanged, and that could go undetected for decades.  If circuitry were permitted in Australia as you have described it, then the chassis of the equipment could float at mains potential and a user touching an audio socket connected to the chassis could receive a fatal electric shock if they were in some other way to connected to earth. 

 

As for your second remark, it is condescending and inappropriate, though I guess you have no knowledge of my background.

I am so sorry, but I am unable to help you.

My background is different to yours and obviously you haven't done the tests and or reading presented. so 

Adure good Man 

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7 minutes ago, MLXXX said:

I have no equipment that provides continuity between the mains cord neutral pin and and the chassis side of an audio socket of the equipment.

You are not using ant device with a switch mode driver then, again you speak in non Engineering/Senior Electrical riddles

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2 hours ago, 125dBmonster said:

You are not using ant device with a switch mode driver then, again you speak in non Engineering/Senior Electrical riddles

Which device do you have (make and model) where the mains neutral pin connects to the headphone socket ground (the body of the socket)?

Edited by MLXXX

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This is all getting a bit loopy for my liking... :blink:  :D

 

1v0xxc.jpg

 

JSmith :ninja:

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