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Tech Head - The Technology Section
The Work Bench and Soldering Station
Humming subwoofer
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<blockquote data-quote="Waveguide" data-source="post: 906733" data-attributes="member: 364636"><p>My guess is the same as others that the filter capacitor(s) in the power supply</p><p>have dried up and no longer make a DC voltage from the output of the rectifier.</p><p><a href="http://electronics.stackexchange.com/questions/73863/cap-value-for-full-wave-rectifier-circuit" target="_blank">http://electronics.stackexchange.com/questions/73863/cap-value-for-full-wave-rectifier-circuit</a></p><p>(check "waveform without capacitor" in the link)</p><p>A multimeter that can measure AC voltage is enough to do a quick check.</p><p>The AC voltage over the capacitor should be a few volts or less.</p><p>At low power (no audio signal) the AC voltage will be close to zero if the filter</p><p>capacitor is OK.</p><p> </p><p>RFI will never give a low frequency hum unless the source is amplitude modulated</p><p>with the exact frequency of the hum. (I once worked in a really fancy EMI-lab)</p></blockquote><p></p>
[QUOTE="Waveguide, post: 906733, member: 364636"] My guess is the same as others that the filter capacitor(s) in the power supply have dried up and no longer make a DC voltage from the output of the rectifier. [url]http://electronics.stackexchange.com/questions/73863/cap-value-for-full-wave-rectifier-circuit[/url] (check "waveform without capacitor" in the link) A multimeter that can measure AC voltage is enough to do a quick check. The AC voltage over the capacitor should be a few volts or less. At low power (no audio signal) the AC voltage will be close to zero if the filter capacitor is OK. RFI will never give a low frequency hum unless the source is amplitude modulated with the exact frequency of the hum. (I once worked in a really fancy EMI-lab) [/QUOTE]
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