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Possible ground loop issue?
Possible ground loop issue?
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Old 4th May 2010, 11:09 PM   #1
atnaat is offline atnaat  Wales
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Default Possible ground loop issue?

I have my computer connected through an M-Audio 2496 directly to an amplifier via line level. When I turn the volume up on my computer to a fairly high level, say half way on the amplifier (30w per channel, speakers 90db sensitivity) a hiss can be heard through both speakers on the computer which subsequently stops when I unplug the phono leads from the amplifier. Also when I turn the volume up to full on the amplifier I can hear fan noise bleeding through the speakers and rhythmic buzzing when I do something on the computer like scrolling down a web page.

My power supply is a OCZ StealthXStream which I have just upgraded to in belief it would lessen some of the problems, I previously had a very cheap OEM PSU.

Is this a ground loop issue or does it sound like the PSU is doing an inadequate job on filtering the supply?

Sorry for the question, just about to start my first DIY Audio project, or electronic project for that matter so this is all very much a learning curve for me.
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Old 5th May 2010, 06:43 PM   #2
Speedskater is offline Speedskater  United States
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Ground loops cause hum and low frequency buzz.
Hiss is often caused by a stage-gain-structure problem. That is the output signal voltage range of the first unit is different than the input signal voltage range of the second unit.
The following is a rather complicated explanation of the problem, but it's all I could find today.

Live Sound: How Do You Set System Gain Structure? - Pro Sound Web
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Old 8th May 2010, 08:16 AM   #3
owenhamburg is offline owenhamburg  Germany
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This a very common issue. I strongly recommend getting an optical connection to an external DAC. It solved the same issue for me. I started a thread about it here;

ATX power supply noise.
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Old 12th May 2010, 09:57 AM   #4
Someone7272 is offline Someone7272  United Kingdom
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Quote:
Originally Posted by atnaat View Post
My power supply is a OCZ StealthXStream which I have just upgraded to in belief it would lessen some of the problems, I previously had a very cheap OEM PSU.
Yeah I got that PSU too, I get a very low frequency, feint hum too, its low enough to be ignored for me. It doesn't get louder or quieter if I turn the amp up or down.
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Old 12th May 2010, 01:21 PM   #5
ThorstenL is offline ThorstenL  Germany
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Join Date: Nov 2002
Hi,

Quote:
Originally Posted by atnaat View Post
Is this a ground loop issue or does it sound like the PSU is doing an inadequate job on filtering the supply?
Practically ALWAYS a groundloop. PC's have the earth attached and usually the PC dumps plenty of noise into it. Usually the HiFi somewhere has another earth.

Smack, bang, you have hum, buzzing bees and all sorts.

The easiest thing to do other than optical connections (which such for SQ) is to use an Isolation transformer that steps the voltage down to 55V-0V-55V with the 0V earthed.

You can now safely remove the earth on the Computers feed, groundloop banished. Of course, if you like to live dangerously simply use a cheater plug on the PC.

Ciao T
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