EXF1 Circuit Kit

$ 149.00

The EXF1 is a premium microphone circuit kit designed to give vintage character to electret capsules. Combine this circuit with our medium-diaphragm capsule to build a microphone with rich tonality, in an easy-to-build package.

If you don't already have your own compatible donor mic body, you can buy an all-inclusive microphone kit with high-quality metalwork here; see the T-25 microphone kit.

About the Audio Circuit

The EXF1 uses a similar circuit design as our best-selling T-84 transformer coupled circuit kit. Both are based on the Neumann KM84. Both utilize custom-wound transformers that help give the circuit its sound. Both rely on manually, individually biased NOS JFETs that we include with each kit.

The EXF1 is optimized for use with electret capsules, and was designed to be very easy to build — without compromising audio quality. See the many 5-star reviews on the T-25 product page.


Included In The EXF1 Kit

  • Audio PCB (US-made, high quality, ENIG process, 2-layer)
  • Transformer mounting board
  • Custom-wound dual bobbin transformer
  • Selected, hand-biased NOS JFET
  • 100% of audio components needed to complete the circuit
  • Detailed, 28-page, step-by-step build guide
  • Tech support via email


The EXF1 should fit most 150mm-180mm condenser mic bodies, including the CAD GXL2400 and Apex 435. It fits the BM-700 and BM-800 donor mics that we've tried.

We cannot guarantee compatibility with any 3rd-party metalwork.

If you'd like to verify fit in your microphone, click the diagram at right to download a PDF template of the ETL1 PCBs, which are the same size as the EXF1 PCBs. Print the document, check that the printed dimensions match your hardcopy, then cut out the paper PCB and hold it against your chassis. Make sure the mounting holes in the PCB line up with the threaded mounting holes in your mic's chassis, as well as verifying that the PCB would physically fit inside the mic body.

All-inclusive Option

See our T-25 Microphone Kit for an all-inclusive option, including a robust mic body, swivel mount, and capsule.

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