RFI problems

laz · 18th February 2004, 10:12 AM

Need help.Ive got a Perreaux 9000B power amp and Perreaux SA2 preamp .Ive made up some leads using good quality shielded mic cable using rca's on the pre going to xlr's on the power.I'm getting rfi{AM radio} coming through when there connected together.When I switch the pre on it gets slightly louder.If i unplug the leads on the pre and leave them plugged in on the power the rfi is gone although volume control doesnt increase the noise when there plugged together.Also is it normal to get loud hum if you touch the rca's body when there not plugged into the pre amp only on the power amp.I've gone from active on the rca to pin 3 on the xlr and neutral on rca to pin 2 on xlr and shield only on pin 1.RE Laz

dhaen · 18th February 2004, 04:27 PM

Going from unbalanced to balanced without a transformer, or active circuitry can cause problems. However, I think you've made them worse for yourself by the pins you have chosen. Try this:
pin 2 - inner
pin 3 - outer (shield)
pin 1 - either leave unconnected, or connect to pin 3

Remember to check the pin numbers on the XLR plug; they're not logical

laz · 19th February 2004, 04:47 AM

Thanks dhaen.I wired the connectors that way because for some reason on the back of the power amp it states that pin 3 is +ve and pin 2is-ve I think Perreaux wired them that way for some reason if i'm not wrong.Do you think I should still drop the shield and/or still wire the the pin1 with pin2.Thanks Laz.

laz · 21st February 2004, 08:06 AM

Also when I used the preamp with a normal perreaux 1150 B poweramp unbalanced the RFI was still a problem.Someone please help!

18th February 2004, 10:12 AM	#1
laz diyAudio Member Join Date: Dec 2003 Location: adelaide	RFI problems Need help.Ive got a Perreaux 9000B power amp and Perreaux SA2 preamp .Ive made up some leads using good quality shielded mic cable using rca's on the pre going to xlr's on the power.I'm getting rfi{AM radio} coming through when there connected together.When I switch the pre on it gets slightly louder.If i unplug the leads on the pre and leave them plugged in on the power the rfi is gone although volume control doesnt increase the noise when there plugged together.Also is it normal to get loud hum if you touch the rca's body when there not plugged into the pre amp only on the power amp.I've gone from active on the rca to pin 3 on the xlr and neutral on rca to pin 2 on xlr and shield only on pin 1.RE Laz

18th February 2004, 04:27 PM	#2
dhaen diyAudio Moderator Emeritus Join Date: Jun 2002 Location: U.K.	Going from unbalanced to balanced without a transformer, or active circuitry can cause problems. However, I think you've made them worse for yourself by the pins you have chosen. Try this: pin 2 - inner pin 3 - outer (shield) pin 1 - either leave unconnected, or connect to pin 3 Remember to check the pin numbers on the XLR plug; they're not logical __________________ John _____________________ Diy site: http://homepage.mac.com/dhaen/OnRyoku/OnRyoku.html Trading site: http://www.keystrobe.com

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19th February 2004, 04:47 AM	#3
laz diyAudio Member Join Date: Dec 2003 Location: adelaide	Thanks dhaen.I wired the connectors that way because for some reason on the back of the power amp it states that pin 3 is +ve and pin 2is-ve I think Perreaux wired them that way for some reason if i'm not wrong.Do you think I should still drop the shield and/or still wire the the pin1 with pin2.Thanks Laz.

21st February 2004, 08:06 AM	#4
laz diyAudio Member Join Date: Dec 2003 Location: adelaide	Also when I used the preamp with a normal perreaux 1150 B poweramp unbalanced the RFI was still a problem.Someone please help!

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