gainclone 5.1 big humm trouble

[stephanegagne]

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 ?

thanks!

Stephane

 

[Puffin]

Probably.

 

[pacificblue]

Schematic? Photos?