The beginnings of this project can be found on this thread on the GroupDIY forums. The actual "ORS87" begins crystallizing only on page 3 of the thread.

Feature list:

• no capsule coupling capacitor
• no exotic components
• no Teflon / PTFE isolation pin required
• option for attenuator pad (lowering capsule voltage)
• option for low-cut / high-pass
• pad & low-cut can either be vertical-mount switches (mechanical modifications to body tube needed), or internal 0.1" pin-headers & jumper-links
• option for additional high-frequency attenuation
• flexible output transformer wiring options
• fits Alctron MC001, Apex 435, BM700, BM800, Focusrite CM25 mk3 (possibly earlier ones as well), M-Audio Nova, MXL 440, MXL 2001, MXL 2006, sE 2200A, t.bone SC400, t.Bone SC450
• v1.1 - added "calibration" input

Construction details:

• C7 selection - DC-blocking output capacitor between the JFET drain and output transformer; several footprint options available (2.5mm-pitch electrolytic, 5mm or 7.5mm-pitch box film, and up to 15mm-pitch axial or epoxy-dipped radial film)
• C12 low-frequency filter - 47nF "stock" value; alternatively, install a 10nF from the component side, and add a second capacitor on the solder side of the board (10nF, 22nF, 33nF etc) until desired low-frequency extension is reached
• C13 high-frequency filter - 220pF "stock" value; alternatively, install a 100pF from the component side, and add a second capacitor on the solder side of the board (22pF, 33pF, 47pF etc) until desired high-frequency attenuation is reached
• RH and CH optional additional high-frequency reduction - 10k & 1nF can provide an additional 2dB of attenuation at 10kHz, if needed / desired (both included in the BOMs, regardless)

Part ordering:

• As it stands, the BOMs contain parts for strictly ONE board / microphone each
• If you wish to order parts for multiple mics, carefully try to do the math for how many of each component you need
• That being said, for the most cost-effective option, do yourself a favor and consider ordering up to the next price break - say, you only need two 47k resistors for 0.093eu/pc (so 0.186eu), but you could get 10pcs for 0.72eu (a bit less than the price for 8pcs). Can't hurt to have more spare parts (especially since they're cheap), for later projects, right?

Mouser BOMs:

• You will need the "ORS87-Plus BOM" (or "FET847 BOM") AND either the "ORS87-Plus jumpers" OR the "ORS87-Plus switches"
• If you're fine with a normal box-film PET capacitor for C7, change the row 3 quantity from 1 to 2
• If you're fine with an electrolytic capacitor for C7, change the row 1 quantity from 2 to 3
• If you wish to use a polypropylene film capacitor for C7, also add the "ORS87-Plus PP capacitor" to your basket
• ORS87-Plus BOM
• FET847 BOM
• ORS87-Plus jumpers
• ORS87-Plus switches
• ORS87-Plus PP capacitor

Digikey BOMs:

• You will need the "ORS87-Plus BOM" (or "FET847 BOM") AND either the "ORS87-Plus jumpers" OR the "ORS87-Plus switches"
• If you're fine with a normal box-film PET capacitor for C7, change the row 8 (FET847 row 7) quantity from 1 to 2
• If you're fine with an electrolytic capacitor for C7, change the row 9 (FET847 row 8) quantity from 2 to 3
• If you wish to use a polypropylene film capacitor for C7, also add the "ORS87-Plus PP capacitor" to your basket
• ORS87-Plus BOM
• FET847 BOM
• ORS87-Plus jumpers
• ORS87-Plus switches
• ORS87-Plus PP capacitor

Further details available in the PDF build guide (attached below).