The electronic module is surface mount, and shares the circuit of the BM-700, K-5000, and other low-cost karaoke mics which I’ve been using for chassis. See analysis here.

So I decided to work with the existing circuit, adding an R-C filter to the voltage regulator output. There isn’t room for through-hole parts, so a trace was cut, solder mask scraped away, and a 470 ohm surface mount resistor installed across the cut. A pair of 47 uF / 16 V solid tantalum caps were installed across the power pads at the input end of the board. Exacting, careful work requiring a magnifier and fine soldering iron. This is not a mod for surface mount newbies.

Added 470R

Added 47uF cap, another on bottom of PCB

Notice that on tantalum caps, the stripe is on the positive terminal.

Having decided to use the existing amplifier electronics, we need to use either an electret capsule or build a very tiny DC - DC converter to polarize a conventional capsule. The capsule which came in the mic is a mid-size brass electret which I haven’t seen before.

It sounds promising, and I’ll investigate it in the future. I also have a sample large diameter electret capsule to work with, so at least initially I don’t have to see how small an oscillator I can build.

All of these electret mics based on this circuit have polarity reversed from standard, that is, the wires from pins 2 & 3 are backwards. This is a side effect of 5V PIP computer sound card compatibility. For studio use on 48V phantom power, that should be fixed. Unfortunately,

there is an error in the PCB layout of these smaller mics at the XLR connector, so moving the output resistors to the alternate pads doesn’t work. You need to cut a trace and run a jumper or two.

There are several capsules on my list to check out, and a couple of capsule mods I’m working on, and one of those will probably wind up in these mics. Stay tuned.