We have offered this in the past and over the course of working on a few, I wanted to update this offering to be more concise and to the point, and more affordable. Think of this as building a somewhat higher end mic with a cleaner build inside the body of your existing original WA-87, using the principle ingredients (blank board, capsule, transformer) but throwing out all the other components and wire.
The mic has a surprisingly decent K87 variant capsule, and a quite good Cinemag transformer, and a decent FET circuit. Where I see the room to improve is really in the build quality and component quality. It's put together pretty messily, to be honest, and this impacts sound... esp. in the High Z section, capsule termination, etc. Component quality is also questionable with some of the choices. I've seen many of these short out or have intermittent performance due to the very fragile and low cost high ohm resistors used (the soldered radial legs tend to break off from wear), and the extremely flimsy internal hookup wiring (particularly on the XLR).
What we do is go through and literally strip down, clean, and de-solder the entire board, and repopulate it with only the highest grade parts everywhere that it matters. WIMA audio grade caps, audio grade polystyrene capacitors, Kemet or AVX brand over-spec'd tantalum capacitors, Nichicon audio grade electrolytic capacitors, and audio grade carbon film and carbon composite resistors. Some of the generic film capacitors are replaced with polystyrenes to open up the sound a bit more. We use silver teflon hookup wire to replace the original internal wiring, and when we are done the board will look clean and immaculate. Most importantly it will be reliable. very reliable. We put in rugged high-value ohm resistors that will never fail, and wire and solder joints that will likewise hold up for the life of the mic.
Sonically, I always felt the mic sounded pretty good but was a bit vanilla and a bit 'veiled' or plastic in its tonality. The mod makes it sound a bit more open and natural, cleaner, clearer, slightly extended, and a touch closer to the source of its inspiration.
WA-87 (original only!) upgrade
Just to be clear, this is an upgrade where you send in your existing microphone. We do not sell the microphone.