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Old 07-09-2021, 11:02 AM   #48
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Join Date: Dec 2013
City & State: San Antonio
My Country: United States
Line Voltage: 120v 60hz / 240v 60hz
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Posts: 563
Default Re: Signal Tracer - Requesting input on requirements

It's white noise. Same level of white noise if the volume is all the way down or turned all the way up (audio input hooked up, but no sound playing). My compuer speakers have white noise if I put my head next to them with the volume all the way down, becomes slightly louder if I turn them up. Can't hear it from 1ft away. The LM386 has constant white noise that I can hear, with the speaker facing away, from at least 5ft away. The noise is loud enough I don't think I could use it to chase down noise in a system I would be troubleshooting.

I peeled the components off the board and put them in my breadboard (pic attached) for troubleshooting. I swapped out the caps that came with the kit for nichicon / kemet and I do think the sound is a touch better, but the noise didn't change. I didn't add in the protection diodes, the led or the resistor from pot to pin 3. When I add the 10uf cap between pins 1 and 8 (200x gain), the noise is overwhelming, so my breadboard layout is probably worse than the PCB, but results without the cap (20x gain) are similar.

A minor miracle has occurred, the electronics shop has some JRC LM386D in stock. From what I have read, that's pretty much the gold standard (if not fake), I'll go pick one up and see how it sounds...

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