Plugged sound card mic into speaker #ubitx

Rob French (KC4UPR)

I've been using my ubitx with the speaker output connected directly to my USB sound card input.  The sound card supplies ~2V for an electret mic, but I figured I was fine since the ubitx output has the 47uF capacitor after the LM386... But I just realized, that is the wrong polarity for a DC bias applied from the USB sound card!  I haven't seen a pop, but am I slowly destroying that output capacitor?

Bryan Corkran, VK3KEZ

I’ve found these work well and very cheap been around for years , use it for Wspr
no drivers needed in windows..


Hi Rob,

What voltage do you read on the other side of the capacitor?  IIRC, there's about 4-6VDC on the output of the lm386.  If so, then your 2V is not going to matter much I think.



Tom, wb6b


In my case I hooked the microphone input of the USB sound adaptor to the high side of the uBitx volume control. That way I don't need to readjust the volume control to get the level correct if I use the uBitx for something else between running WSPR/Digital modes, and I can listen to the digital signals if I wish.

The signal level from the high side of the volume control, at least with the USB sound adaptor I have, is a little on the high side, so optionally you could put a couple of resistors in a voltage divider to lower the signal level a bit.

Tom, wb6b