How to reduce 120hz harmonics?

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ahgu

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reduce 120hz harmonics?

My TL074 OPAMP has gain of 40dB, and I see 10-20mV of 120hz, 240hz harmonics at the output. I think my ground noise is at 0.1mV, the LDO says it has 30-40uV RMS. Is it a good ground plane with noise of 0.1mV? I think I did the layout pretty good with ground plane and signal separation.

But the 120hz harmonics is a little too high and shows up on the speaker, how can I remove or reduce the harmonics?


And is it possible to reduce the ground noise even lower?

thanks
ahgu
 

Hi

Check the PS filter. Just a capacitor might do the trick.

post your circuit and layout for details.

madhukar
 

check for source

You can do a few experiments to find where it is coming from. First disconnect the input to the amplifier and short it to ground. Does the hum go away? Power the circuit from a laboratory quality power supply. Does the hum go away?
 

If you use only 1 opamp input try to insert blocking capasitor on other input with enough capasity to filter 120 Hz .
 

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