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Old 9th January 2003, 01:09 AM   #1
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Default oscillation 101

How can you tell if an amplifier is oscillating without using an oscilloscope?
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Old 9th January 2003, 01:38 AM   #2
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it may exhibit a hiss or whistle
it may run hot at idle
it may burn a small resistor accross the output
if you can monitor the mains current it may raise with a load
if it's at a low level it's hard
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Old 9th January 2003, 02:53 AM   #3
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Unfortunately, smoke is usually the first and only sign of the bad sine. In fact, even with a good scope, such oscillations may be too high for it to see.

Of course if the amp has a stable design to begin with...
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Old 9th January 2003, 05:43 AM   #4
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Default Oscillation

Might I suggest mysteriously blowing tweeter fuses too. Sounds like an amplifier is trying to be a transmitter, eh?
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Old 9th January 2003, 07:53 AM   #5
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A lightbulb in series with a 100nF -> 1uF capacitor on the output works. The cap blocks any DC content in the output but AC oscillations pass straight through lighting the bulb for all to see.

Obviously, you need to size the bulb to your power rails.... A 12v car bulb with a series resistor would work.

Nice one,
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