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Need guidance with audio amp project
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Need guidance with audio amp project

by marine_hm on Fri Jun 11, 2021 3:33 am

I need help with learning audio amplifiers.
Just a simple project. I wanted to amplify the sound from a stethoscope just for fun.
I have:
PAM8302 item #2130 for amplification
flat 25mm Piezo with 2 wires (red,black)
2 other audio microphones which have 3 wires. Assuming red and black are for + -, the yellow wire for audio out.

Would the yellow wire be digital or analog or does it matter?

Can I hook up the piezo directly to the PAM8302 board? Which Pins?
The other 2 microphones, which pin for the yellow wire?

marine_hm
 
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Re: Need guidance with audio amp project

by adafruit_support_mike on Mon Jun 14, 2021 11:04 pm

marine_hm wrote:Can I hook up the piezo directly to the PAM8302 board?

It probably won't hurt to try.. connect it to the + and - output pins.

marine_hm wrote:The other 2 microphones, which pin for the yellow wire?

It may or may not be possible.

The PAM8302 can't take input directly from a bare mic. The microphone signal needs to go through a preamplifer like the MAX4466 first:

https://www.adafruit.com/product/1063

A microphone is basically a resistor whose value changes with sound pressure. That change doesn't mean anything by itself. In most cases you put the mic in a voltage divider with another fixed-value resistor to turn the change of resistance into a changing voltage. The actual change in voltage is small.. usually +/-5mV at most.

To turn that into a useful audio signal, you have to increase the voltage swing to about +/-1V. The circuit which does that, like the MAX4466, is called a 'preamplifier' whose job is to scale the voltage up with as little distortion as possible. Then the signal goes through a power amplifier that makes the signal strong enough to drive a speaker.

The circuit techniques that make a good preamp make a lousy power amp, and vice versa. It's easier and more effective to split the job into two parts than to try and make one circuit that does both acceptably.

If your microphones have built-in preamps, the red and black wires are probably power, and the yellow wire is probably the output. You'd connect the mic's GND wire (probably black) to the PAM8302's A- input, and the yellow wire to the A+ input. You'll also need to connect power to the remaining wire (probably red), but will need to know the mic's required supply voltage.

If your mics don't have a built-in preamp, you'll need to run the signal through something like a MAX4466 before sending it to the PAM8302.

adafruit_support_mike
 
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Please be positive and constructive with your questions and comments.