Troubleshooting Amplifier Design and PCB Layout

[Enzy]

I use it to test every other amplifier that I build and it plays them well and the other amplifiers I don't test them with preamps.

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also remember that a Fet is getting extremely hot and I dont know why

 

[Audioguru]

Which Mosfet gets hot, the N-channel Mosfet or the P channel Mosfet?
Measure and post here the voltage across the two 0.2 ohm source resistors and the gate-source voltage for each Mosfet with no input signal.

 

[Enzy]

N channel fluctuates between 0.5v and 350 mv when the transistor is cool it doesn't fluctuates that much it more steady but at the lower mv range link 30 to 70 mv. The P channel Fet fluctuates between 0.6v and 350 mv both Fets get warm until they both get hot, I cant touch the P channel but the N channel is cooler. when I tested across each 0.2 ohm resistor the one connected to the N channel I only got 0.1 mv the one connected to the P channel I got 19mv

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I did all testing in DC with no signal using my multi meter, the only scope I have is a cheap portable version, the DSO nano I could use it to aid if needed.

 

[chuckey]

It sound as though your FETs/amp is oscillating, it could be in the VHF frequencies. Build a RF diode probe and use it to feed your DVM, use a 1000pF coupling cap so it will ignore audio frequencies, which you would hear from your loudspeaker. Now you can measure and see if there is some RF volts about your circuit. If there is, then a 100 ohm resistor in series with each FET gate lead might be enough to kill it- wire the resistor as close as possible to the FET. It could be that your supply lines need to be decoupled to RF on the PCB, use some .1MF on both supplies to earth.
Frank

 

[c_mitra]

Please check the same voltages with the input shorted with a wire. Oscillation at the RF frequency can be destructive. Please use decoupling capacitors liberally.