MicParts MPV57 PCB instructions?

[Paul W]

I bought a used Microphone Parts mic that has some issues, and I'm looking instructions for their MPV57 (rev III) PCB, particularly with respect to the wiring options (omni or pad switch on the PCB) and the HF deemphasis options. (What component do I change, and what values do what?)

I contacted MP and they wouldn't give me the instructions. They said I could send the mic in for repair (at some cost, I assume) if I don't like the way it sounds. Bah.

I believe in the right to repair (and mod) so I'm asking for anybody who's got the instructions to DM me the relevant bits. (I'm not going to distribute them or give away any secret sauce, if they have any. This is just for my personal use.)

 

[Khron]

Photos of the front & back of the board, perhaps?

 

[RuudNL]

The pad switch usually places a small capacitor (in the pF range) in parallel with the microphone capsule.
In omni both membranes of the capsule are in parallel, in cardioid the rear membrane is decoupled.
For the 'corrective EQ' (as MP calls it) a capacitor is switched in parallel with the drain resistor (and eventually one in parallel with the source resistor) of the FET.

 

[Khron]

(and eventually one in parallel with the source resistor) of the FET.

Wouldn't that boost the highs?

 

[RuudNL]

Yes, no doubt! But it seems different values are used for the 'drain' and the 'source' capacitor.
I never liked this solution for 'de-emphasis', because it also increases distortion.

 

[Dylan W]

Pretty sure it’s just a Schoeps circuit with minor modifications. If you post photos of both sides of both boards, and any component values you can see, we should be able to help you.

 

[Paul W]

"A" board front:


The blob of solder connects the near left pin of the switch to one leg of T3, one end of R9, and the whitish wire, which connects to the front diaphragm. (Nothing is connected to the rear diaphragm, whose wire has been snipped.)

"A" board back:


"B" board front:


The light blue wire from the pad marked BP goes to the wired-together backplates.

"B" board back: