Lm4780 problem, 3.5V on output when power on...

[jackinnj]

Originally posted by jaste
Wait a second, I havent tried it with a source yet.
All my measurments have been without any source. To me it sounds strange that the chip would get very hot when the power is on but there's no input but maybe that's the way it is and my amp is actually working just fine? If it's so I shouldnt have my amp on when there's no source?

I'm gonna bet that without any input source your LM4780 is oscillating. It would be helpful if you had a scope. You might be picking up some RFI, or oscillating of its own volition.

FWIW, I have been able to get the LM4780 to oscillate as high as 1.5 MegaHertz -- and it gets very unhappy.

[Peter Daniel]

LM4780 chips produce more offset than LM3875s

It is highly recommended to always have the source connected when amp is on, if no source is connected it's best to short the input to ground.

With source connected, the DC offset us usually much lower too, as the input impedance is in parallel with source's output impedance.