Hi,
After few tests of the implemented system (attached schematic), the FQA6N90C seems to be OK, even in the worst case it never exceed 70°C.
Now I'm facing an other weird problem. When the amplifier is pushed, so when the current increases, the system tend to oscillate.
The result : when the signal peaks, I can hear a loud hum/hard clipping (at 100Hz..?) in the sound. It's getting worse when the switch is on the low position (so when Vds is the bigger).
The peak current is well below the current limitation of R67/D5 so it is not the problem. I also tried without C40, no change.
The weirdest : when I connect my DMM between GND and the positive terminal of C24, it works like a charm, no oscillations and weird noises.
I suspect a layout problem, the oscillation created by the radiance of another component but... Am I missing something else ?
Thanks