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Old 23rd January 2013, 03:17 PM   #1
diyAudio Member
Join Date: Jan 2013
Default gainclone 5.1 big humm trouble

HI !

I build 5 channel gainclone with lm4780.

I use 3 independent PSU module with the same 700VA toroidal.
(all my test with PSU is okay)

I build 3 independent AMP module
my setup is :
1x LM4780 for front L-R
1x LM4780 for surround L-R
1x LM4780 for center channel
(all 3 module have same test result and work very well independently)

but when I plug it in the same 7.1 preout OUFFF ! big hummm noise !
I unplug the center channel and the noise stop .

I read 4V between the RCA INPUT ground of each 3 module ?!

By the way, the lm4780 is not isolated to the heatsink, but each amp module have independent heatsink isolated by wood part. (this is a problem?)

Anybody have tips to help me to find solution ?


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Old 23rd January 2013, 05:51 PM   #2
Puffin is offline Puffin  United Kingdom
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Join Date: Feb 2006
Location: U.K
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Old 23rd January 2013, 06:19 PM   #3
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Join Date: May 2008
Schematic? Photos?
If you've always done it like that, then it's probably wrong. (Henry Ford)
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