SQ-KM84-0.9.0 PCB

[Bo Deadly]

Here's a Neumann KM84 PCB I just did for an MXL 440 donor body but I think the board would work with a lot of other mics:

Here's the zip of gerbers I submitted to OSH Park. It should work equally well with other fabs.

SQ-KM84-0.9.0.zip

This is the stock KM-84 circuit. No changes other than adding a trimmer for bias.

Although in this particular build I used a K47 capsule. And I used a 2SK170 (instead of the usual 2N3819) so I changed the trimmer to 5K and associated bias resistor to 1.5K. And I left out the 47R resistors (there are solder jumps for this) so that I could use 47u / 330p LC filters on the outputs (I didn't put these on the board because they need to be right on the pins to stop RF from getting in).

Sounds good (although I thought the MXL sounded fine too). Here is the response:

and just for comparison the response of the original MXL 440:

Clearly the response is flatter (superior capsule?). Schoeps style circuit is quieter and has less distortion though.

 

[ln76d]

Don't know circuit you are using, but if there is capacitor between FET and capsule front diaphragm, then remove it and change capsule connection like in the "JB schematic".
Use 2N3819 and then measure response.
Also i would remove at least on internal mesh layer.
I don't know  your measurement equipment setup so hard to judge anything what's in your graphs.

 

[Bo Deadly]

Don't know circuit you are using, but if there is capacitor between FET and capsule front diaphragm, then remove it and change capsule connection like in the "JB schematic".
Use 2N3819 and then measure response.
Also i would remove at least on internal mesh layer.
I don't know  your measurement equipment setup so hard to judge anything what's in your graphs.

It's the Neumann KM84.

I know a lot of folks like to move that cap to the other side of the capsule but this PCB follows the stock circuit. No mods.