n00b support for mic & speaker circuit

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darkroastdan
 
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Joined: Tue May 23, 2023 3:09 pm

n00b support for mic & speaker circuit

Post by darkroastdan »

Hey there,
I'm trying to wire up a circuit with a MAX4466 mic + preamp combo, a speaker amp, and a 3W 4 Ohm speaker. When I first switched on the circuit, I was greeted by a very loud, high-pitched chirping noise.

When I first hit the issue, I was using a PAM8302 for my speaker amp. Since I was worried that I broke the onboard trim pot (it could be turned indefinitely in either direction), I ordered a replacement as well as a second MAX4466 (to rule out damage to the initial unit) and a separate speaker amp (MAX98306). I also tried hooking up a 3.5mm TRS jack to the amp output and monitoring through headphones. I adjusted the gain using both the onboard trim pots and via the jumpers on the MAX98306. I also tried installing a 10K potentiometer (mostly so I could stop being deafened by the chirping). Unfortunately, with all of these various hardware configurations, the issue persists.

I can get the chirping to stop as long as I lower the gain on any part of the circuit (e.g., via the onboard trim pots on either the pre-amp or the speaker amp, and/or via the 10K pot), but at these levels, the resulting audio is quet and scratchy and I have to practically eat the mic just to hear any sound. As I increase the gain, the speaker hiss gets relatively loud and, after a point, the chirping will kick in. If I try to find a middle-ground between these two points, any input from the mic will start up another chirp-fest.

I have looked through some of the other posts here in the forums and it sounds like others have run into this before as well. Unless I missed a post, I haven't seen any solutions that resolve the issue. I have studied the product description pages, the data sheets, and some of the tutorials and it doesn't seem like I'm missing anything. My soldering skills are intermediate and I am relatively confident there are no cold solder joints.

I've attached a diagram of my circuit.
Here's a link to a video of the problem occurring.
Any help would be much appreciated!
Attachments
Amp.png
Amp.png (34.21 KiB) Viewed 71 times

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