2020-06-23 LM386 1W Mono Amplifier Input Jack Reconfig

A year or so ago I bought a few 1W mono amplifiers from a Chinese eBay seller for cheap – see the attached photos. The only marking on the PC board is YX-1667 but I’m not sure if that’s the potentiometer or the PC board itself.

I found that if I pushed the 3.5mm plug all the way in to the input jack like it’s supposed to be, it didn’t have continuity, I had to leave the plug pushed halfway into the jack for it to work. So I just left it that way. I checked the jack and it was connected to the volume control improperly, the Ring was connected instead of the Tip.

So now I decided to correct the problem. I also found that the input had a 0.1 uF (104) ceramic capacitor between the jack and the volume control, which isn’t needed for DC blocking because there is no DC; however it does roll off the low frequencies so I decided it wasn’t needed, but it can be left in the circuit.

I decided to put a short insulated jumper wire between the outermost unused jack pin directly to the pin of the 100k potentiometer. I soldered it like shown in the PC side of the board, being careful that the jumper didn’t short to the grounded copper foil that is close to the jack pin.

Another way to do this would be to cut the pad from the soldered jack pins in half. Then solder a jumper from the outermost unconnected jack pin to the capacitor half of the cut pad. This will keep the capacitor in the circuit.

.End of this blog post.


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