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Old 07-06-2021, 07:40 PM   #42
redwire
Badcaps Veteran
 
Join Date: Dec 2010
City & State: Alberta
My Country: Canada
Posts: 2,202
Default Re: Signal Tracer - Requesting input on requirements

It shouldn't get really quiet like that. Unless the speaker GND is shorting out the input signal or something?
I couldn't make out all the wiring, this pic might help. The hookup wire is a bit thick and awkward, I take wire out of old junk stuff like inkjet printers are reuse it. In case this starts to drive you nuts.

The PCB has the speaker ground (JST) trace go around and over to the input jack, and the IC GND is at the the other end of the trace. Sigh. It's not the greatest.

I would the leave the 2.2uF cap where it is, and move the DC power GND up to where the DC jack GND is or C6(-).
Then the signal ground is from the pot GND that goes to pin 4. The input jack GND is far away so I would prefer to not use it. If you must use those input jack pads, I would cut the trace to it and the LED/or to it and at the corner, and run a jumper from the pot GND at pin 4 to the input jack pad. Getting rid of the long loop this board has there, look at the path from input jack GND to the IC lol.

Ideally you want to have the four major grounds: DC power, loudspeaker, IC, signal input - all connect to one point or the star. It's not usually a big deal but some LM386's I built up get finnicky and I have to redo things. The IC has no markings on top?
R2 4k7 is only in if really strong signals coming in, I would leave it out.

It's normal for this to pickup noise and hum when nothing is connected to the input. Putting your hand near it will bring AC hum. It should always be quiet if the pot is turned down though.
Attached Images
File Type: jpg LM386_pcb1.jpg (218.8 KB, 7 views)
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