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I tried to make a microphone (condenser microphone) amplifier that powers a 0.5W 8 ohm speaker using the LM386, however I have been having random noise issues.

Whenever the power is connected, the speaker will output a random high pitch frequency and turning the potentiometer will cause the pitch to raise or lower. Sometimes when I tap the microphone there is a break in sound, however, if I expose the microphone to audio like music nothing happens and the random high pitch noise continues to play (note that this also happens if the microphone is not exposed to any sound.) I am thinking that it may have to do with the fact I am using a breadboard. Do you have any ideas?

Here is the circuit I am using:

enter image description here

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  • \$\begingroup\$ Is your microphone within hearing-distance of your speaker? \$\endgroup\$
    – glen_geek
    Apr 5, 2020 at 13:21
  • \$\begingroup\$ Yes, but I have tried covering it with sound absorbent materials to the point where it is barely audible, however, the buzzing remains so I do not think it is a feedback issue. \$\endgroup\$
    – Jackson Medina
    Apr 6, 2020 at 14:16
  • \$\begingroup\$ Of course the speaker output can be heard by the microphone and is causing acoustical feedback howling because the amplifier gain is 200 times. The power supply has no filtering capacitor so its output is probably bouncing up and down with the oscillation and feeding into the amplifier input through R2. Where is 0.5W coming from? the datasheet shows only 0.14W with severe distortion (the buzzing instead is a smooth tone). Get rid of the breadboard. \$\endgroup\$
    – Audioguru
    May 16, 2021 at 12:00

2 Answers 2

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Sounds like you built an oscillator instead of an amplifier.

Try removing V1 to reduce the gain and see if the circuit stabilizes.

Try making R1 a low value, more like 10Ohm, not 10k.

Or try adding a small R value on the output. Something on the order of 47 Ohm.

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  • \$\begingroup\$ The lower resistance value definitely with the gain. \$\endgroup\$
    – Jackson Medina
    Apr 6, 2020 at 20:39
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Try adding a 100nF capacitor across the voltage supply between pins 4 & 6.

R1 should be 10R not 10k.

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