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Two microphones with their head baskets off, showing red circuit boards and silver capsules
Photo: DJJules (Jules Ryckebusch) via Instructables, CC BY-NC-SA. Resized and converted to WebP.
General · Microphone Other DIY

OPA Alice Microphones (cardioid and figure 8)

Two studio microphones, a cardioid and a figure 8, made by fitting an op-amp circuit and a good capsule into a cheap mic body

Designed by DJJules, published on Instructables

CC BY-NC-SA No commercial use Build info 5/5

Licence verified on Instructables, 21 October 2026.

Get the plans on Instructables ↗ Watch the build
Build type
Electronics (not 3D-printed)
Difficulty
Medium-hard: one small surface-mount chip to solder
Capsule
TSB2555B electret (cardioid); a figure-8 version too
Donor body
A BM-800 or BM-700 mic (about $20, per the author)
Builds
Over 150 of this circuit, per the author (March 2022)

About the OPA Alice microphones

Jules Ryckebusch (DJJules) builds microphones for musician friends and studios. Here he replaces the poor electronics in a cheap BM-800 condenser mic with a quiet impedance converter built around a dual op-amp, and pairs it with a TSB2555B electret capsule. The mic runs on standard phantom power from your interface or mixer.

The guide explains the circuit section by section, including RF filtering at the XLR connector. The circuit board was designed by a colleague and is shared on PCBWay under CC BY-SA, so you can order it there; the Instructable includes the schematic, a board drawing and an Excel parts list. Everything except the op-amp chip is through-hole.

He then builds two mics: a standard cardioid, which he calls great for vocals, and a figure 8, which picks up sound from the front and back and which he says solves some sound-isolation problems when recording. A troubleshooting PDF added in 2022 covers common mistakes.

Who it's for. Home-studio musicians who can solder and want a much better mic than the donor body alone. This page summarises the author's guide; we haven't built one ourselves.

What you'll need

Materials

  • A BM-800 or BM-700 microphone to use as the body

Bought parts

  • A TSB2555B electret capsule (or a figure-8 capsule)
  • The OPA Alice circuit board (a CC BY-SA shared design you can order from PCBWay)
  • The op-amp and parts from the author's parts list
  • 2 × 22 nF capacitors for the XLR connector
  • M2.5 screws, small rubber grommets and E6000 glue
  • Optional: a capsule saddle

Tools

  • A soldering iron with a fine tip and flux
  • A screwdriver
  • A multimeter for troubleshooting
  • An audio interface or mixer with phantom power

Build overview

Our own outline. The schematic, parts list, troubleshooting PDF and build video are on Instructables.

  1. Build the board. Tack and solder the op-amp chip first, then the through-hole parts.
  2. Strip the donor mic. Unscrew the BM-800, remove its board and capsule, and keep the screws and XLR connector.
  3. Prepare the XLR. Solder the two 22 nF capacitors to the connector and add short colour-coded wires.
  4. Mount the capsule. Glue the capsule to its saddle and fit grommets to damp handling noise.
  5. Assemble and test. Fit the board and capsule into the body, connect phantom power and test, using the troubleshooting guide if needed.

Videos

Play video: The full build (loads YouTube)
The full build, Sound Sleuth (the author's channel). Plays from youtube-nocookie.com after you click.
Play video: A recording made with these mics (loads YouTube)
A recording made with these mics, Sound Sleuth. Plays from youtube-nocookie.com after you click.

Nothing loads from YouTube until you press play. Video thumbnails are © their creators.

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