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Old 14th July 2012, 03:47 PM   #1
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Default Squeal on turning off Rotel.

My Rotel RA-930AX has a high pitched squeal shortly after I switch off, rapidly dropping in volume.

What might this indicate?

As it happens it also has DC offset of about 80mv on each channel, which on another thread I was told is likely by design.

There's a schematic here, if anyone feels the need.
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Old 14th July 2012, 04:07 PM   #2
DF96 is offline DF96  England
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Probably means that one of the frequency compensation components has changed value, so the amp is now only conditionally stable. That is, it begins to oscillate as the open loop gain decreases as the supply rails reduce on switch off. An unfortunate speaker load (or strange cables) might contribute too.
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Old 14th July 2012, 06:46 PM   #3
RJM1 is offline RJM1  United States
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It could also be power supply capacitors, I've seen this problem in some amplifiers when one rail voltage collapses quicker than the other. Check the power supply voltages to the output transistors with a DVM on DC and see if there is a difference of more than a couple of volts.If there is, measure the voltages on the AC setting and you should see a larger AC voltage on the rail with the lower DC value . If there is replace both filter capacitors.

Last edited by RJM1; 14th July 2012 at 06:57 PM.
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Old 15th July 2012, 08:28 PM   #4
djk is offline djk
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Try tacking some 22F electrolytics across each of the main filter caps.

I find as the main filter caps age that many amplifiers will make a 'squeeg' sound when turned off.

The bypass caps usually eliminate this sound.
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