Electronics > PCB/EDA/CAD

Noisey (as in audio freq) PCB

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First post.  I have a PCB with a transistor amplifier which works in the audio to ultrasonic frequency range.  Quite often you can hear high pitch squeals coming from the board.  Unusually the input impedance is quite low ~1k and I think the noise is coming from a 100nF ceramic 0805 HPF capacitor.  Having said that touching almost any part of the board changes the sound so I can't be sure.

Any ideas how to get rid of it?


A capacitor with a better dielectric (eg. X7R instead of Z5U) or film instead of ceramic might help. See this thread about a similar topic.


You didn't say when this noise happened.

Does it happen when a particular signal is being amplified or with no signal?

It's the sound of the signal!  It's normally something like a 6-10kHz wave.  Sine-ish!

Are you saying that you are getting some kind of mechanical resonation from the PCB ??
I.E. Sound is comming from a component not from another source?

Or that the PCB is generating its own signal. I.E. Oscillating? If it is oscillation then pressing fingers across the track might change the frequency slighty..


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