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Old 31st January 2015, 02:08 PM   #1
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Join Date: May 2013
Default Ground loop pc powered speekers

as the title says,i have ground loop problems when i connect power of amplifier to PC power in the pc box,is there a easy cheep way to fix this ,thanks
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Old 31st January 2015, 05:02 PM   #2
phofman is offline phofman  Czech Republic
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Join Date: Apr 2005
Location: Pilsen
I would try connecting the supply ground wire not to the PSU wire, but right next to the audio jack where jack ground is hooked to. That should eliminate the noise between supply ground and incoming signal ground lines.
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Old 1st February 2015, 08:02 AM   #3
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Join Date: May 2013
no change, same as normal ground to ground

here is scratch of the problem imgur: the simple image sharer

any suggestions
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Old 1st February 2015, 08:43 AM   #4
phofman is offline phofman  Czech Republic
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Join Date: Apr 2005
Location: Pilsen
What type of noise do you experience?

If the power ground comes from the same point as your signal ground, the only ground currents are those within and to your amp, no PC currents can be involved. Of course the supply positive line has the fluctuations superimposed, but I would assume an amp should be immune a bit against fluctuating supply line (stabilizer, filter). Nevertheless, it is possible the currents within/to the amp itself cause the noise too.

I used to have the same setup (just like you originally) and could hear mouse move, letters typed on keyboard, appearing on screen in terminal. I did not research the various options for ground connection, but built a simple separate mains-powered no-earth-connection 12V PSU for the amp right away instead. The setup has been dead silent since.
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Old 1st February 2015, 09:49 AM   #5
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Join Date: May 2013
I have separate power for amp ,and it sound perfect no noise,
but i want it to be powered by PC.
Are the some type of ground lifting some 100 ohm resistors,i google it but
cant figure it out
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Old 13th November 2015, 11:25 PM   #6
dekromm is offline dekromm  Italy
diyAudio Member
Join Date: Oct 2015
This is exactly the thread I was looking for!
Unfortunately there's not a solution yet.
I'll explain my situation (and I think i's just the same as turbogt16v's).

What I have:
- A tower pc and
- A low-power class-D amplifier board. (low-power class-D amplifier board (supply voltage 12V)

What I did:
- I powered the amplifier with 12V taken from the pc's power supply (I wired it to one of the unused molex connectors)
- I connected the motherboard's audio out into the amplifier via a jack-to-RCA cable
- I connected a little speaker to the amplifier's output

What I got:
- The amplifier turns on when I turn on the pc
- Noise that gets worse when moving the mouse (if it can be of help i'll post a recording of the noise)

What I tried:
- The same amplifier with the same source (pc motherboard) and with an external power supply (not the pc's) works fine, no noise.
- the same amplifier with the same power supply (pc's) and with a different source (batery powered phone) works fine, no noise.
- the same amplifier with the same power supply (pc's) and with a different source (pc-powered phone) doesn't work fine: the noise is back.

So, these trials made me think of a ground loop issue.
I'll soon try as phofman suggested, connecting the amplifier's ground to the negative signal.

turbogt16v, do you have any more information about that 100ohm resistor you were talking about?

Thanks in advance
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Old 16th November 2015, 11:36 PM   #7
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Join Date: Nov 2004
Location: Germany
It is a ground loop issue. You have two ground connections, one via the signal cable and another via power ground.

You'd probably have to hack the amplifier PCB so you can separate input signal ground from power and output ground, maybe with a ~100 ohm resistor || 10-100 nF capacitor still connecting the two. Once you have managed to do this, you'd also want to reroute the bias cap at pin 16 of the TA2024 so that instead of pin 8 AGND it goes to your input ground.

If that sounds like a rather daunting task, I guess you're best off sticking with an external power supply.

Unfortunately it is not possible to convert a circuit with this IC to balanced input, which could save a lot of headaches.
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Old 17th November 2015, 10:23 AM   #8
Cookj is offline Cookj  Belgium
diyAudio Member
Join Date: Aug 2004
Location: Bruxelles
Get yourself one of these or similar:

Monacor FGA30 Stereo Line Transformer Ground Loop Isolator
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