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Humming for laptop + USB + Chordette Qute


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I posted in power cable but NFA advised me to put it here as this is a common problem:

 

When I connected Qute to laptop initially I had no problem.

 

Last night I tried to connect dvd player + coaxial to Qute, i had humming in speakers, removed the dvd, the humming was still there, uhm, I tried to remove one by one and reconnect one by one separatedly to pinpoint the cause and finally it was the usb cable connecting Qute to laptop that caused it.

 

I then tried laptop on battery, remove laptop from docking station, humming was there.

 

I earthed Qute to chassis of amp, the humming reduced.

 

I rebooted laptop, humming reduced, not as annoying as I almost didn't hear it from listening position but if leaned my ear against the speaker the humming was there (it wouldn't be good for speakers would it?)

 

I'm sinking of buying a USB ground isolator :

http://www.ebay.com.au/itm/Olimex-USB-ISO-Full-speed-USB-isolator-1000VDC-audio-dac-noise-ground-earth-loop-/271418726563?pt=AU_Home_Personal_Security&hash=item3f31d118a3#ht_743wt_1358

 

Would it fix the problem?

 

Please educate me a bit more about this and any advice to fix the problem will be appreciated.

 

I attached my connection diagram for clarification.

 

Cheers, Tung

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Hi Tung,

 

Ground loops in the digital arena don't always produce a hum in the speakers.  First place that I would look is in the analogue stage which means interconnects, amplifier and speaker cables.  Maybe check to see that the power cords and signal cables are well separated...if you brought something new into your system (such as the DVD player) then maybe you have a power cord  in a bad spot.  Second thing to check is that the laptop and dac are connected to the same power board or socket...if they are on separate circuits then the electrical connection between them is a little more difficult to diagnose.  Thirdly I would change interconnects and/or speaker cables just to make sure they are not damaged...anything will do...if the hum goes away when you change your interconnects you know that is the problem.

 

I would hold off on that USB isolator until everything else has been eliminated.

 

Cheers,

 

Anthony

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That is a very helpful diagram.

 

Two questions:

  1. Does the Qute come with a two prong power cord (i.e. with no protective earth)?
  2. Have you tried running the active subwoofer from your diy powerboard?  I think this may help straight away.

Anthony

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1. Qute comes with 2 prong.

2. I have not tried active subwoofer from DIY power board, i will try it tonight.

 

I read that 2 prong should be separated from 3 prong, so what I'll do is: Amp + SW to DIY power board (3 prong), laptop on battery, Qute and USB hard Drive on another power board, may be with extension chord from opposite wall rather than the 2 wall outlets side by side on the same wall as per my diagram. I could try to run USB hard drive on battery and possibly Qute on battery as well.

 

If any improvement, I will post the results.

 

Can you guys do a simple test for me: lean your ear against the speaker when amp is on to see if any light humming or not at all (absolutely nothing)?

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The dac and the computer need to be plugged into the same power-board or power socket, so don't switch the Qute over to the diy power-board just yet.  Ideally you would keep your amplifiers together but at the moment you have one on your diy power-board and one on the power-board for your digital gear, which is probably not the best from a ground loop perspective.

 

Most people will have a little hum in their speakers.  It is not ideal but many do not bother to eliminate because it is a bit hard.  I know a guy with 118dB speakers that has zero audible hum...that is special...but it takes a bit of effort to get to that level.  I have hum in my 88dB speakers which varies depending on the amplifier that I am using, but I usually have to put my ear up to the tweeter to hear it).

Edited by acg
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I have tried all of your suggestions with no difference.

I made a USB cable with no ground wire (No.4) and no effect either.

Currently I switch back to SBT to enjoy and forget that annoying USB/laptop humming for a while.

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The dac and the computer need to be plugged into the same power-board or power socket, so don't switch the Qute over to the diy power-board just yet.  Ideally you would keep your amplifiers together but at the moment you have one on your diy power-board and one on the power-board for your digital gear, which is probably not the best from a ground loop perspective.

 

Most people will have a little hum in their speakers.  It is not ideal but many do not bother to eliminate because it is a bit hard.  I know a guy with 118dB speakers that has zero audible hum...that is special...but it takes a bit of effort to get to that level.  I have hum in my 88dB speakers which varies depending on the amplifier that I am using, but I usually have to put my ear up to the tweeter to hear it).

Why do the dac and computer need to be in the same power-board? I have my dac on my dectet board and computer in the wall power point for convenience. Most of my hum is not in the speakers but comes from the Amp.

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Why do the dac and computer need to be in the same power-board? I have my dac on my dectet board and computer in the wall power point for convenience. Most of my hum is not in the speakers but comes from the Amp.

 

They don't _need_ to be, most computers, dacs and any associated USB converters will work plugged in wherever you wish,but they are all electrically connected to each other (via power and usb grounds) so the idea is to keep the ground loops between the bits of gear as short as possible by plugging them all in to the same power board.  I doubt that you will hear a hum if any of this digital gear is not grounded optimally, but there could be increased noise that affects the operation of the digital part of the dac and maybe the analogue part as well.  

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I have tried all of your suggestions with no difference.

I made a USB cable with no ground wire (No.4) and no effect either.

Currently I switch back to SBT to enjoy and forget that annoying USB/laptop humming for a while.

 

Ok.  My suggestion would to start from as simple a system as possible that still involves the dac.  So I would take out the subwoofer (unplug it from the power-board as well as from the amp) and run the dac and the laptop without the external hard drive (which should be disconnected from the computer and power-board as well).  So laptop > Qute > Amp > Speaker with nothing else plugged into either of your audio circuits at all.

 

If you still have a loud hum then swap USB cables.

 

What happens then?

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I tried the bare necessity: amp + speakers: some humming (put ear up to tweeter/mid to hear), then add DAC: same level, add usb for laptop: loud.

Connect all power to 1 wall outlet, 2 outlets (2prong and 3 prong separatedley) no fidderence.

I think the amp may be the starting point, then worsened with laptop/usb.

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