BM-800 Condenser Microphone Small Board Quick Shots


Last year in an excess desire to get into microphone modding and picked up the "Profession BM800 Condenser Microphone Bundle" by Zingyou and from "TDL Technology" on Newegg. For $25 + tax after promotions and shipping "free" (included), seemed good enough to play around with. Turn out, the guts weren't quite what I expected from my advance research on the BM-800/BM-700 and similar models frequently used for a cheap donor shell and moddable amplifier board. Plus being a minimum functional microphone with proper phantom power. Here's this small PCB one I got:

green printed circuit board with two large capacitors and a number of surface-mount electronic components screwed into a die-cast metal frame that makes up the BM800
Small board inside this version of the BM800 microphone.

Taking a closer look, here's what's on the circuit board. The XLR polarity was inverted, as expected, once I traced out the schematic (more on that in a future post). It has your usual three PNP, one NPN, and K569 prebiased FET plus the regulator 9V zener diode as reference. The two-layer board is about 35x20 mm and is labeled with the part number "BM-868-A" and "X-MAX-AUDIO". Most of the rear side is a ground plane with only a couple traces required for routing.

unscrewed printed circuit board of this BM800 to get a closer look at the surface mount electronic components
A closer look at the board components.
 

I did a complete reverse engineering of the schematic, but that will need to wait until I can get it presentable and prepare some of the digital aids I made in the course of that work for publishing online. As expected, it basically matches the expected schematic for this sort of well-iterated/well-copied design being produced at minimal cost. With a more generous pad placement than some of the other designs seen, it does make for decent modding, too.

The microphone element is a 16mm electret in a large plastic frame, as expected for the lower end of this model. Replacing it will be an even further out project to consider.

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