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Came across a few circuit components and I thought I'd have a little fun. I don't understand what's happening though. I implemented this circuit.

schematic

The only differences were: I didn't have a .1uF cap, so I used the smallest one I had which is 1uF. For the input I used the adafruit max4466 mic amp. For the output I didn't have the 10k pot so I just didnt put anything. And the speaker was a 6 ohm speaker I got out of an ipod speaker I found at the dump!

Problems/Questions:

  1. The speaker transmits the sound from the mic. If I put a song on my phone very quiet and press it up to the mic amp microphone the speaker is very loud. If I move a centimeter away, the sound isn't really amplified.
  2. Voltage from ground to the output pin of the op amp is 0.
  3. Voltage across (+) (-) of speaker is zero.
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    \$\begingroup\$ That's an electret mic on the front end. The circuit isn't intended to have a preamplified mic at the front. That's what the circuit does. Or is supposed to do. \$\endgroup\$
    – Ian Bland
    Sep 4 '17 at 3:31
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    \$\begingroup\$ So, you gave us a schematic but your circuit is completely different? Why is this tagged LM386? Did you look at the application circuit for the MAX4466? Also, rather than using a op-amp/mic pre to drive a speaker (not something it's designed to do), consider using a power amplifier that is designed to drive speakers. You could even cascade the mic pre with the power amp.. \$\endgroup\$
    – uint128_t
    Sep 4 '17 at 5:38
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    \$\begingroup\$ You don't actually say what is wrong. You list observations and all these observations seem reasonable given the information you have provided. So, in conclusion, this circuit sounds like it is working perfectly given that an LM324 was never intended to drive a 6 ohm speaker and your microphone may not be properly acoustically set up for making judgements about an audio source. \$\endgroup\$
    – Andy aka
    Sep 4 '17 at 7:57
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Julian, regarding the fact that the mic amplifies well when you are very close to it, but it the volume drops a lot as you move a little away from it could be due to the type of mic you are using. I'm not so sure, but if you are getting a good amplification of the sound, without much distortion, I think it's more of a limitation of the mic than of the amplifier.

What I think is more relevant to point out to you here is that you seem to be using the DC mode of your multimeter to measure an AC signal. Multimeters are not very good at measuring this type of signals but you should be able to see some variation in voltage in the output of your amplifier when you are amplifying some sound. So try changing the knob of your multimeter to the symbol that has the V with a "~". That will measure the AC voltage in the output of your amplifier which would be the sound signal.

No using the 10k pot in the output of the amplifier may overload the speaker, but if that is the case, you will hear the audio distorted and likely the op-amp will overheat.

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  • \$\begingroup\$ I know this question refects a lack of understanding of alot of things. I'm reading the MAKE book on electronics and it has breadth, but I was curious about this particular circuit. Your input was very helpful. I think, judging by this question's reception, that going forward I should either pick my EE coworker's brains or just keep reading books and wait until enlightenment comes. \$\endgroup\$ Sep 4 '17 at 14:19

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