Forgot to tell you - the IRF3710Z transistors work just fine. Thank you again.
But now next problem with a same HIP4080-type amp. Changed all power supply FETs, half output FETs with IRF3710Z (other side IRF3710-s remained), HIP4080 and some protection diodes near HIP4080. Now the amp works again just fine but there's an audible whining noise coming through speaker. The pitch of the noise changes slowly and sometimes stops at all. If you move the PCB or any component on it the pitch changes. I've tried resoldering the PCB, but still no luck. Any ideas?
But now next problem with a same HIP4080-type amp. Changed all power supply FETs, half output FETs with IRF3710Z (other side IRF3710-s remained), HIP4080 and some protection diodes near HIP4080. Now the amp works again just fine but there's an audible whining noise coming through speaker. The pitch of the noise changes slowly and sometimes stops at all. If you move the PCB or any component on it the pitch changes. I've tried resoldering the PCB, but still no luck. Any ideas?
That's normal for many of the hifonics amps. I'm assuming it's at a low level. It's generally not an issue because the woofers can't reproduce the high frequencies well and they're generally in the trunk of the vehicle which further reduces the level of the noise. Many class D amps have their power supply synchronized to their output oscillator but these have no synchronization so they whine a bit sometimes.
It is low level, about 800mV peak to peak, but louder than these amps usually are. There is also 1.2V DC offset.
Maybe something to do with the output filter(s)? Many class d amps have this output whine and like Perry said, you can't usually hear it through the woofers + being in the trunk usually eliminates that possibility.
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