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darth vader

Annoying earth hum issue using USB

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@125dBmonster I had a bit of a look for a isolation transformer. They seem pricey, even for one with a low current rating.

 

I guess it would make sense to borrow one and see if that fixes the problem. I'm still using optical for the meantime.

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On 2/13/2018 at 6:53 PM, MLXXX said:

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

@125dBmonster, if you have such a device it would not meet traditional Australian safety standards. Australian safety standards have classified the neutral as a live conductor (even though under normal operation it should remain at near earth potential).  The safety guidelines about connecting the power plug neutral to exposed metal parts of a consumer appliance may be less stringent in certain overseas countries.

 

The below is extracted from an older version of Australian standards known informally as "test and tag" and used extensively for workplace safety inspections. I would be surprised if the requirements had been relaxed in the updated version of it, AS/NZS 3760:2010 In-service safety inspection and testing of electrical equipment.

 

I suggest you look into whether your equipment that connects its power plug neutral to an exposed metal part of the equipment is approved for use in Australia.  If it is, then that represents a relaxation in Australian safety standards of which I am unaware.

 

Edit: One reason for the traditional safety requirement of not allowing the power point neutral to be exposed to a human test finger is that in the event that the connection of the power point neutral back to the switchboard failed, the neutral would be able to float up to near full mains potential if some device was plugged in to one of the affected power points and switched on.

 

Quote

 

 

page 20   AS/NZS 3760:2001   Note: this version of the standard is out of date and cannot be used.

 

B3 TEST CONDITIONS

NOTE: A live part is a conductor or conductive part intended to be energised in normal use, including the neutral conductor. The protective earth conductor is not a live part.

 

B3.1 Class I equipment – Live parts to exposed metal parts (earthed) Insulation resistance is measured between live supply conductors and exposed metal parts, with the mains switch/selector on the equipment in the ‘ON’ position. The resistance shall be not less than 1 MΩ. Alternatively the current in the protective earthing conductor with the equipment operating may be measured. The measured current is not to exceed 5 mA.

 

page 21  AS/NZS 3760:2001 Note: this version of the standard is out of date and cannot be used.

 

NOTES: 1 Figure Bl shows testing of insulation resistance of exposed metal parts. 2 Mineral insulated metal sheathed heating appliances can have an initial insulation resistance of less than 0.01 MΩ after storage for an extended period. This may be rectified by suitable remedial action. 3 Exposed metal is defined in Clause 1.4.6 and is required to be earthed.

 

B3.2 Class II equipment – Live parts to external metal parts (not earthed) Insulation resistance is measured between live supply conductors and external metal parts, with the mains switch/selector on the equipment in the ‘ON’ position. The resistance shall be not less than 1 MΩ.

 



 

 

Edited by MLXXX

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16 hours ago, darth vader said:

@125dBmonster I had a bit of a look for a isolation transformer. They seem pricey, even for one with a low current rating.

 

I guess it would make sense to borrow one and see if that fixes the problem. I'm still using optical for the meantime.

 

Your 2014 iMac uses a three pin IEC power connector at the back and would be earthed.

 

The suggestion to connect the Line magnetic DAC power plug and the iMac power plug to the same power board was a good one but you must have tried that by now and must have found it didn't solve your hum problem.  That suggests to me that the nominal ground the iMac uses for its USB output socket is not at exactly the same potential as the power cord earth the iMac uses.  That situation is more likely to arise with a full size computer with its higher power consumption and larger physical layout, than it is with a laptop. (Also with a laptop you can temporarily operate it solely with its own battery power, and avoid any earth connection!)

 

Apple themselves recognize an earth loop issue can arise and provide a number of suggestions: https://support.apple.com/en-au/HT201781   However the suggestions don't specifically cover USB cables.

 

@125dBmonster's suggestion of an isolation transformer for the iMac but maintaining the earth connection might work, but the fact the earth connection to the iMac would be maintained suggests to me it is very possible it would not solve your hum problem.  It would still be possible for the iMac's USB socket nominal ground potential to differ from the mains power plug ground potential.

 

Can you tell us what model Line magnetic DAC you use?  If it has a healthy buffer size and well-designed reclocking I'd have thought it could sanitize an incoming optical feed very effectively!

 

Of course another approach would be to get your hands again on a laptop set up with USB drivers and do careful A B comparisons between it and your iMac with optical. Unless the laptop delivered noticeably better sound there would seem to be no reason not to continue using your existing iMac optical interface!

 

Edit: If you are really determined to use your iMac USB interface then you could consider a so-called USB isolator, intended for stereo audio and hum reduction. I see that has already been suggested to you, earlier in this thread,  but I think care would be needed to choose an appropriate model. [I haven't researched this in any depth but the HiFimeDIY isolator looks promising.]

Edited by MLXXX

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Its an LM-502CA

 

I've pretty much settled on optical for the time being. Its working pretty well.

 

I see any gains from using USB as slight, I have other areas in my system I can improve and hopefully gain more from them. Once they are done I can re visit the USB thing.

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Fair enough.

 

 

 

 

 

 

 

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On 12/02/2018 at 10:45 AM, 125dBmonster said:

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

Maybe.   Not necessarily with USB, as it's not always the typical "ground loop" type of issue.

 

@darth vader does the noise worsen/change when something moves significant on the screen (eg. dragging a window around), or if you move the mouse around?

Edited by davewantsmoore

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I cant really say @davewantsmoore as I've settled on optical for the meantime. Its a bit hard to say.

 

As it stands using optical to DAC and Ardivarna as the source player, its been woking reasonably well. Optical has been hum free and surprisingly detailed. 

 

Theres always the artistic impression factor though

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Here's a way to connect USB and isolate all PC noise from making it to the DAC. I use one of these and added a linear power supply to boot to keep all switching noises away from the usb cable entirely:

https://www.megabuy.com.au/startech-1port-usb-20-over-cat5-or-cat6-extender-p856371.html

It allows you to connect usb devices far away by converting the data to something that can be sent over an ethernet cable and then recreates the usb at the far end with a powered receiver so doesn't use the PC's usb power at all. I tried cheaper ones and they didn't work. This was the most reliable one that wasn't too expensive that I could find.

 

It basically emulates what this far more expensive device from psaudio does:

http://www.psaudio.com/products/lanrover-usb-transporter/

Despite what psaudio says about that device, it's just a relabelled one of these:

http://www.icron.com/products/icron-brand/usb-extenders/cat5/usb-2-0-ranger-2301/

Edited by Ittaku

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On 15/02/2018 at 5:29 PM, davewantsmoore said:

 

@darth vader does the noise worsen/change when something moves significant on the screen (eg. dragging a window around), or if you move the mouse around?

@davewantsmooreWhat would this suggest?

 

My setup for HT has a high pitch whine. You can see my chain in my sig. HPTC -> HDMI -> AVR-> Integrated Amp - > Front L/R channels have  a high pitch noise the other speakers do not.

For music I run USB -> Audiophilleo -> (a DAC) -> Integrated -> Front L/R and there is no noise, so the Audiophilleo is doing its work

 

All plugged in to the same power board. I know it's coming from the HTPC and the HDMI is simply acting as the conduit, just unsure why the AVR doesn't send the hum between the speakers it powers but the integrated which is getting its signal from the AVR pre-outs does have a hum?

Edited by roh008

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2 hours ago, roh008 said:

I know it's coming from the HTPC and the HDMI is simply acting as the conduit

So if you unplug the HDMI the noise goes away immediately?

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15 minutes ago, davewantsmoore said:

So if you unplug the HDMI the noise goes away immediately?

yes, pretty sure it does do it immediately. Were you thinking it was the difference between the AVR and the integrated amp?

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I'll preface this post with everything below is at your risk...

 

Most overseas laptop power supplies only have active and neutral connections.

Most Australian laptop power supplies have a 3 pin connection (active/neutral/earth)

 

Laptops run from batteries and/or the low voltage DC (typically less than 20V DC) output from a "wall wart".

 

If your noise issue exists when the laptop is running from batteries, then you need to look elsewhere for the noise issue.

 

If your noise issue exists only when you plug your laptop power supply into a power point (assuming 3 pin connection), then let's explore more.

  • given the noise issue started when connecting the laptop to 240V, then the issue could be related to noise on active, neutral or earth

Never muck with 240V wiring unless you know what you're doing - 240V kills

  • disconnecting the active or neutral will obviously stop your device working. If you disconnect the neutral and the device keeps working you have a major house wiring issue - your RCD should have tripped!

Never muck with 240V wiring unless you know what you're doing - 240V kills

 

I've seen many others disconnect the earth pin on laptop power supplies with miraculous results - I would never recommend this approach.

 

Remember never muck with 240V wiring unless you know what you're doing - 240V kills

 

Let's examine the risks of this approach (which I don't recommend):

  • the power supply develops an internal fault presenting 240V to the case of the wall wart. The case is plastic, so no risk of electrocution
  • a fault in the power supply presents a high voltage on the positive wire of the low voltage output - Most laptops have plastic cases so low electrocution risk, but a higher likelihood of laptop damage
  • A fault in the power supply presents a high voltage on the negative wire of the low voltage output. Similar to above, most laptop cases are plastic, so the risk of electrocution is low. But a high likelihood of laptop damage
  • In my experience laptop power supplies when they fail just stop providing DC

Remember never muck with 240V wiring unless you know what you're doing - 240V kills

 

I've seen many situations where others have disconnected the earth pin on low voltage gear with good results.

 

Remember never muck with 240V wiring unless you know what you're doing - 240V kills

 

cheers

Mike

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5 hours ago, almikel said:
  • a fault in the power supply presents a high voltage on the positive wire of the low voltage output - Most laptops have plastic cases so low electrocution risk, but a higher likelihood of laptop damage
  • A fault in the power supply presents a high voltage on the negative wire of the low voltage output. Similar to above, most laptop cases are plastic, so the risk of electrocution is low. But a high likelihood of laptop damage

Although the case of the laptop may be plastic, its 3.5mm phono socket for analogue audio output will be metal, and will typically be connected to one side of the incoming DC supply. The audio socket is one place where an electrocution risk could arise. Theoretically, anyway.

 

5 hours ago, almikel said:

Most Australian laptop power supplies have a 3 pin connection (active/neutral/earth)

Yes, both my Australian laptops have a 3 pin plug for the external DC power supply, and the power plug earth is connected to one side of that DC supply output.

Edited by MLXXX

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On 18/02/2018 at 5:57 PM, roh008 said:

yes, pretty sure it does do it immediately. Were you thinking it was the difference between the AVR and the integrated amp?

Unplug everything else from the AVR, and see if the problem goes away.

 

If you have a TV connected to the AVR, then disconnect it, especially   (does it have a powered TV antenna or foxtel connected?)

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Unplug everything else from the AVR, and see if the problem goes away.
 
If you have a TV connected to the AVR, then disconnect it, especially   (does it have a powered TV antenna or foxtel connected?)


Ok but to get the high pitched whine noise (soft though that it is) i will need to leave the pre amp rca cables in right? As the noise is only from the front L/R channels when the integrated is set to AV mode.
The Center speaker and rear speakers don’t have this noise (and are powered by the avr)

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2 hours ago, roh008 said:

Ok

 

Yes.   Just leave ONLY what you need connected.

 

ie.  only  HPTC -> HDMI -> AVR-> Integrated Amp - > Front L/R channels

 

You can leave the other speakers connected to the AVR too.

 

Unplug everything else from the AVR.  eg. TV, other sources, etc....   See if it changes.  If not.   Try:

 

Make something move significantly on the screen of the HTPC.    Eg.   get a single window up, and move it around on the screen.   Does this make the noise change? (sometime the noise can be caused by 'activity' on the video system)

 

If still stuck, try disconnecting everything non-essential from the computer too, to see if that changes things.

Edited by davewantsmoore

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Earth hum....hmmmm.... maybe it is the prince of darkness calling you :fear:

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On 2/22/2018 at 6:44 PM, Decky said:

Earth hum....hmmmm.... maybe it is the prince of darkness calling you :fear:

Earth hum ?

could be a Venus Hum

 

the princess of peace

 

 

 

 

 

 

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Posted (edited)
16 minutes ago, Sunshine Superman said:

Earth hum ?

could be a Venus Hum

 

the princess of peace

 

 

 

 

 

 

That was EXCELLENT!

Edited by LogicprObe

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I feel OP's pain, as I also have humming/noise issue between my AVR, Integrated Amp, TV and speakers.  Mine involves RCA, AC power, aerial and HDMI connections. 

 

I tried almost every check/ combinations of plugging and unplugging... and also went to Jaycar to buy a ferrite rings, ground loop isolator etc, NOTHING WORKED!!!!  I am not an electrician, so after many many hours , I gave up... 

 

While I cannot find a fix, I did managed to isolate/avoid the problem, I must unplug (or give up) any 1 of the 3 connections when listening to music to get rid of loud hum:

- RCA cables between integrated amp and AVR, or

- HDMI cable between TV and AVR, or

- Aerial from wall to TV.

 

Probably no help to anyone but that's my experience.

 

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15 minutes ago, att23 said:

I feel OP's pain, as I also have humming/noise issue between my AVR, Integrated Amp, TV and speakers.  Mine involves RCA, AC power, aerial and HDMI connections. 

 

I tried almost every check/ combinations of plugging and unplugging... and also went to Jaycar to buy a ferrite rings, ground loop isolator etc, NOTHING WORKED!!!!  I am not an electrician, so after many many hours , I gave up... 

 

While I cannot find a fix, I did managed to isolate/avoid the problem, I must unplug (or give up) any 1 of the 3 connections when listening to music to get rid of loud hum:

- RCA cables between integrated amp and AVR, or

- HDMI cable between TV and AVR, or

- Aerial from wall to TV.

 

Probably no help to anyone but that's my experience.

 

Sad to hear, att.  :(

 

In my last house I suffered hum when I selected the feed from my Foxtel box / VHS recorder into my preamp.  (These were both in the next room to my preamp.)

 

What solved the problem was plugging the TV, Foxtel box and VHS recorder into a 1KVA isolation transformer - instead of direct to the wall.

 

IOW, TV, Foxtel box and VHS recorder were plugged into a 1KVA isolation transformer ... whilst the preamp was plugged directly into the wall, in another room.

 

So you might like to try getting hold of an isolation transformer, to plug your TV - and possibly your AVR - into.  I don't use mine any more - so it is available ... but would be expensive to ship to Sydney.

 

Andy

 

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I think problem here might be related to AVR, most if not all of them aren't earthed (just 2 pins on IEC socket) , maybe grounding cable connected to chassis could help? or grounding cable between AVR and integrated (chassis to chassis) ? 

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