'New' Power amp introduces hum - help? - diyAudio
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Old 17th March 2012, 09:26 PM   #1
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Join Date: Feb 2012
Location: Newport Beach, CA
Default 'New' Power amp introduces hum - help?

My system:
TW cable box (HD) with HDMI connection to receiver
Sony BDP s5570 Blu Ray and SACD player conected to receiver
Pioneer VSX-1121-K receiver
Cambridge Audio ID100 dock connected to receiver via s/pdif

Front speakers: Martin Logan Ascent
SW: Martin Logan Dynamo 300
center and surrounds: Swans D 3.2

New component: Perreaux PMF 2150B power amp (200Wpc @ 8 ohm, 400Wpc @ 4 ohm).

Issue: As soon as I introduced the Perreaux to the system and powered it up, I got audible hum (like groud loop hum) from the Martin Logan Ascents, even when the Perreaux was the only component powered up.

I tried hooking the Perreaux up to a different power outlet, but no difference.

I'm loking for options / suggestions here. Is it the cable box like so may posts seem to suggest? And if so, will a Axiom Audio ground isolator do the job?

Or is the problem strictly tied to the Perreaux? If so, what can I do here?

I welcome all feedback and suggestions.
Thank you for our help.

Last edited by pvanosta; 17th March 2012 at 10:25 PM.
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Old 18th March 2012, 02:16 AM   #2
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Join Date: Feb 2012
Location: Newport Beach, CA
Update:
I added a ground lift adapter (one of those things that converts your 3 prong plug to a 2 prong) to the power amp and changed nothing else.

No noise. Deadly silent amp now.

So the next question is: how do I get the same effect in a safer way?
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Old 18th March 2012, 03:50 AM   #3
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Join Date: Nov 2009
Location: Los Angeles
Quote:
Originally Posted by pvanosta View Post
Update:
I added a ground lift adapter (one of those things that converts your 3 prong plug to a 2 prong) to the power amp and changed nothing else.

No noise. Deadly silent amp now.

So the next question is: how do I get the same effect in a safer way?
When you said you had hum when only the power amp was on, was the rest of the equipment still connected but powered down? Have you tried connecting things one at a time until it hums? I had hum issues with antenna cables (not cable TV) with computers connected in different rooms on different branch circuits. What I got were 'ground lifters' (galvanic isolators) for the antenna coax from these guys.

RMS Communications Inc.

In your case the first thing I'd try is disconnecting the cable from your cable box as the cable 'ground' and house 'ground' are not the same and may have loop currents. With a DVM you could measure Voltage differentials between the cable and the cable box. I predict some small offset. Even more telling would be to check the current between the cable and the cable box. It's the current that causes the problems. You're looking for both AC _and_ DC Voltage / current offsets. If it IS the cable the isolator will fix your problem.

G
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Old 18th March 2012, 11:50 AM   #4
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Join Date: Nov 2002
Generally the cable box is causing the problem. Stratus has given you a link to a issolation transformer that should end the noise problem. We are not permitted to suggest the elimination of the ground thru a ground adapter here on the forum.
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Old 18th March 2012, 04:04 PM   #5
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Join Date: Feb 2012
Location: Newport Beach, CA
Understood and thank you. I will experiment with the cable box today.
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