Autotek MX 1300 2 channel amp

So this amp came to me with the complaint of low output and overheating. I found 4 swollen rail caps so I replaced them. I have checked the drives and followed the audio signal through the amp with my scope all the way to the speaker terminals and I can’t find any issues.

The power supply produces +57.2 vdc and -56.7 vdc. The 10 rail caps are rated at 63wv.

I checked the regulation on the power supply and I can see changes in the duty cycle with amp under load so I can assume the power regulation is working as it should.

What else should I check?

The amp is stone cold. Granted I haven’t driven it hard.


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I had it on one of my amps, that a resistor in the pre amp circuit was damaged. Directly on the op amp for the input. So i had only 20% of Output.. It sounds normaly to me, but it was realy to low. I injected a 200Hz signal with a Generator. Measured the output and was able to compare. I needed 8V of Input to reach max output with gain full in.