One of my latest projects was to design and make a microphone pre-amp supplied by USB power.
I built it, using two 34063's for a +18 and -18 rail, and a LT1171HV to supply the 48v phantom power for the microphone.
The main amplifier is an SSM2019; a chip with quite nice specs. I basically copied the design on this
https://www.analog.com/media/en/technical-documentation/data-sheets/ssm2019.pdf on page 7 at the bottom. I'm using a capsule from an ADK 51s microphone; one of the leads goes to the center of the Mylar membrane and the other connects to the outer case of it.
I tried last night to attempt to record and see if I could get any sound from the amplifier, hooking it up to my computer via a 3.5 mm audio jack.
Upon recording, (turning the gain up to the max of about 200 ish) I just get a TON of noise, and 60 hz interference gobblygook, and absolutely no sound from the capsule itself.
My questions are;
Is this a ground loop issue? Through the noise I can't hear ANYTHING from the microphone so...
Am I connecting the microphone capsule up correctly? Or do I need a different design? As I said before, one of the capsule leads connects to the mylar membrane itself, and the other to the outer brass case.
Do I need to get an audio transformer?
If any of this is unclear, or if you feel like you need more information I could try to put together a schematic.