Personal Voice Amplifier Background Hum Trouble

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SUMMARY

The discussion centers on troubleshooting a personal voice amplifier circuit that experiences a loud buzz when using a 3V class A preamp with a dynamic mic element. The circuit includes a 100k audio taper potentiometer and a 6V LM386 amplifier set to a gain of 200. The buzzing issue is resolved temporarily by grounding the potentiometer with a finger, suggesting potential grounding or shielding problems. The user has substituted polyester capacitors for ceramic ones, which may contribute to the issue.

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  • Understanding of audio circuit design principles
  • Familiarity with LM386 amplifier specifications
  • Knowledge of dynamic microphone operation
  • Basic skills in using an oscilloscope for signal analysis
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Electronics hobbyists, audio engineers, and anyone involved in designing or troubleshooting audio amplification systems.

riley_cultist
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Long-time lurker, first post, here goes.

So I'm working on a personal voice amplifier for a face mask. I have the dynamic mic element ("www.accusonicproducts.com/pdf/G01A009-PFK.pdf2FVVVHLD_Q" ), which feeds into a 3v class A preamp, through a 100k audio taper pot, to a 6v lm386 amp with the gain set for 200.

The problem is that there is a very loud buzz present while using the preamp, which is not present while using on the lm386 amp. However, if I put my finger across the pins for the potentiometer the sound clears and be comes noticeably louder and operates correctly.

The only difference between my circuit and the one schematic I linked to is that I substituted polyester caps in place of the ceramic, I didn't think it would make much difference, but I could be wrong.

Schematics available on demand.

I'm at my wits end, any help would be appreciated!
 
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You need to post the schematic and preferably a picture of your circuit. It is hard get what you circuit is by reading.
 
riley_cultist said:
Long-time lurker, first post, here goes.

So I'm working on a personal voice amplifier for a face mask. I have the dynamic mic element ("www.accusonicproducts.com/pdf/G01A009-PFK.pdf2FVVVHLD_Q" ), which feeds into a 3v class A preamp, through a 100k audio taper pot, to a 6v lm386 amp with the gain set for 200.

The problem is that there is a very loud buzz present while using the preamp, which is not present while using on the lm386 amp. However, if I put my finger across the pins for the potentiometer the sound clears and be comes noticeably louder and operates correctly.
Could well be mains hum. You might not have good shielding, or the Earth braid might not be connected properly, or might be earthed in the wrong place. You are using coax for all audio leads?

Examine the audio on an oscilloscope and determine its frequency, is it identical with your mains frequency? Then probably your finger is performing the earthing function.
 
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