SDC Mics: Say hello to my little friends

I’ve been building Transformer Coupled LDC mics for a while now. My BFM (Big F’n Microphone) circuit is adapted from the Neumann KM-84 (kleines Mikrofon – 84) circuit with very minor differences from the original. I have finally gotten round to building some SDC mics with another adaption of the BFM circuit called the TFM (Tiny F’n Microphone).

Donor Bodies

Donor bodies are plentiful for these mics. From MXL alone, there are 551, 991 603s and 840 (and maybe more). The 551s and 991s are usually in a set with a 550 or 990 respectively, but sometimes we can find them alone.

TFM Circuit

The TFM really is pretty tiny. There is not a lot of wiggle room on the board – especially when a large chunk of the board is taken up by the Transformer. Fortunately the KM48 and our derivation of it is a very simple circuit and within a few revisions of the board, everything is fitting and working out well. As with the LDC bards, the capsule and FET wiring is off board and using Keystone insulated turrets for the point-to-point wiring.

Transformers and Capsules

I’ve been building my BFM boards with either CineMag or AMI transformers, but will now be offering the 3U GZT-84 Transformer. The tone is slightly brighter than the CineMag or AMI and it it seems to have a bit more harmonic distortion in the low frequencies than the others. And this is largely what gives transformer mics their sound.

For capsules, I am offering options from 3U Audio. Their capsules come in several polar patterns apart from the standard cardioid and they sound amazing. Because the capsule is easily field-replaceable, you can get several capsules for your mic and swap in the one that is appropriate for what you are trying to capture.