SDC Mics

We mod and rebuild common pencil mics from MXL such as the 991, 551, 603s and 840. These are Transformer Coupled mods using our TFM (Tiny F’n Microphone) circuit which is derived from the Neumann KM84. We offer a variety of high quality capsules from 3U audio and Transformers from CineMag, AMI and 3U Audio. All prices and options details are outlined below. For specific questions, don’t hesitate to contact me. Or you can go straight to the Store and see all of the offerings.

the circuit

SDC Microphone Mod

The TFM circuit board fits small pencil style mics from MXL (and maybe others). Like the bigger sibling, the BFM, this circuit features low noise high quality components and is hand assembled in our shop in Newport, RI. The capsule and FET are wired point-to-point using high quality insulated turrets.

Too Loud?

The circuit supports a fixed pad which can be added at no cost for high-spl applications (Snare top, bottom, hat or other loud percussion applications).


Capsules for these are only available from a couple of sources. We’re offering capsules by 3U Audio in our builds. Besides the standard Cardioid pattern, they are available in Omni and Hyper-Cardioid patterns. Unlike an LDC, you can get multiple capsules and swap them for different applications. The SDC capsules from mic-parts work too.