Amp hum when RCA cable is connected

xeclipse · 17th December 2011, 04:52 PM

Hi,
I have two amps: one (mono) for subwoofer and the second (stereo) am trying to connect to the same psu.
One case houses the mono amp and the transformer. The stereo amp has its own rectifier and filter caps and connected to the power transformer inside the case.Both amps are silent with no RCA cable connected. There is a hum when the cable is connected without the source.When I connect the source(pc)and break the ground loop between the inputs of the two amps,there is a hum from one of the amps(the one whose ground input is disconnected).
How can I solve this problem?
Regards.

jcx · 05:12 PM

Ground Loop Isolator - RadioShack.com

or for 10x the price:

JENSEN TRANSFORMERS, INC. - ISO-MAX® CI-2RR Stereo Audio Input Isolator

Whitlock's seminar handout paper is really good intro to the issues:

http://www.jensen-transformers.com/a...%20seminar.pdf

magnu · 17th December 2011, 08:17 PM

Try rotating the power plug, switching the AC input pins. In a few cases can this remove the problem.

Ian Finch · 17th December 2011, 08:23 PM

Quote:

Originally Posted by magnu

Try rotating the power plug, switching the AC input pins.....

Swapping Active For Neutral?

jaycee · 17th December 2011, 10:00 PM

Ian, there are some countries that dont have polarised power outlets. However in these countries, neutral and ground are usually never bonded together, and neutral is treated as a "live" line. Neutral to ground shorts will trigger an RCD in such cases.

Ian Finch · 18th December 2011, 01:42 AM

Quite so...We are not all MEN system but a little qualification is in order -hence the "shock horror" rather than objection.

Ian Finch · 02:34 AM

Ok - now you have me curious but couldn't locate the details of Kenya's earthing system. The system is officially using UK outlet fittings,
so it will require a little work to swap connections over but that also suggests a good reason not to try it.
Is this reference info correct in Kenya, Xeclipse?
Leads Direct - Mains Wiring

xeclipse · 18th December 2011, 05:35 AM

Quote:

Originally Posted by Ian Finch

The system is officially using UK outlet fittings,.......
Is this reference info correct in Kenya, Xeclipse?
Leads Direct - Mains Wiring

That's correct,a three pin plug but I have connected only two:live and neutral(the amp is in a wooden case). The pc has all the three connections.
Regards.

Lavcat · 18th December 2011, 07:57 AM

I second the suggestion of the Jensen ISO-MAX. I have an ISO-MAX between my computer and my preamp. I'm currently building a box that will have four more Jensen transformers in it for isolation.

17th December 2011, 04:52 PM	#1
xeclipse diyAudio Member Join Date: May 2010 Location: Where the world's best tea come from:Kericho Kenya	Amp hum when RCA cable is connected Hi, I have two amps: one (mono) for subwoofer and the second (stereo) am trying to connect to the same psu. One case houses the mono amp and the transformer. The stereo amp has its own rectifier and filter caps and connected to the power transformer inside the case.Both amps are silent with no RCA cable connected. There is a hum when the cable is connected without the source.When I connect the source(pc)and break the ground loop between the inputs of the two amps,there is a hum from one of the amps(the one whose ground input is disconnected). How can I solve this problem? Regards. __________________ if there are no sparks,it probably doesn't work!

17th December 2011, 05:03 PM	#2
jcx diyAudio Member Join Date: Feb 2003 Location: ..	Ground Loop Isolator - RadioShack.com or for 10x the price: JENSEN TRANSFORMERS, INC. - ISO-MAX® CI-2RR Stereo Audio Input Isolator Whitlock's seminar handout paper is really good intro to the issues: http://www.jensen-transformers.com/a...%20seminar.pdf Last edited by jcx; 17th December 2011 at 05:12 PM.

18th December 2011, 01:42 AM	#6
Ian Finch diyAudio Member Join Date: Apr 2010 Location: Coffs Harbour, on the east coast	Quite so...We are not all MEN system but a little qualification is in order -hence the "shock horror" rather than objection. __________________ regards

18th December 2011, 02:31 AM	#7
Ian Finch diyAudio Member Join Date: Apr 2010 Location: Coffs Harbour, on the east coast	Ok - now you have me curious but couldn't locate the details of Kenya's earthing system. The system is officially using UK outlet fittings, so it will require a little work to swap connections over but that also suggests a good reason not to try it. Is this reference info correct in Kenya, Xeclipse? Leads Direct - Mains Wiring __________________ regards Last edited by Ian Finch; 18th December 2011 at 02:34 AM.

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17th December 2011, 08:17 PM	#3
magnu diyAudio Member Join Date: May 2010 Location: Stockholm	Try rotating the power plug, switching the AC input pins. In a few cases can this remove the problem.

17th December 2011, 10:00 PM	#5
jaycee diyAudio Member Join Date: Apr 2004 Location: Norwich, UK	Ian, there are some countries that dont have polarised power outlets. However in these countries, neutral and ground are usually never bonded together, and neutral is treated as a "live" line. Neutral to ground shorts will trigger an RCD in such cases.

18th December 2011, 07:57 AM	#9
Lavcat diyAudio Member Join Date: Dec 2009 Location: New Jersey USA	I second the suggestion of the Jensen ISO-MAX. I have an ISO-MAX between my computer and my preamp. I'm currently building a box that will have four more Jensen transformers in it for isolation.

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