Microphone Mod Service

We do extensive rebuilds of low cost condenser mics replacing the circuitry and capsule with high quality discrete components. These are not kits from mic-parts or anyone else. Our Transformer Coupled and Transformerless Circuit Boards are hand assembled with care at the shop in Newport RI, USA. Highest quality components, point-to-point Capsule wiring, attention to detail and a lot of love go into every mic. We’ve worked on many different mics including MXL 990, MXL 910, MXL 550, MXL 440, MXL v250, MXL v63m, MXL 2001, Sterling Audio ST55, Rode NT2 (and many more) Questions? Contact us.

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Hear the improvement to a typical low cost MXL microphone (in this case a MXL 990). The stock mic has a small diameter capsule (despite looking like an LDC) and a mass-produced surface-mount circuit board.

We replace the capsule with a quality LDC (K47 or CK12 style), and the circuit with our all discrete jaSb board. Each board is hand assembled, component-matched and tested.

Why do a Mic Mod/Rebuild?

To hit the price point, low cost mics are often using Small Diaphragm Condenser (SDC) Capsules. The circuits are mass produced with low cost surface mount components. The result is a thin, dull tone with an over-sibilant top end. The photo shows a typical mass-produced MXL board next to our hand-assembled board. The circuitry is similar but the performance is vastly improved! We individually hand-bias the FET in each board for optimum performance and do point-to-point wiring between the capsule and the FET.

microphone mod circuit with discrete components
Typical MXL board (L) and my jaSb (R)


We offer Transformerless and Transformer-Coupled rebuilds using our jaSb and BFM boards respectively. Both flavors are hand-assembled using high quality components and feature point-to-point wiring between the capsule and FET. For transformer coupled builds, we offer a choice of boutique quality transformers. For LDC capsules, we have K47 style center-terminated or CK12 style edge-terminated.

How it works

  • Choose the mic mod you want and select the options. As always, if you have any questions about options or want help choosing, contact us and we’re glad to help.
  • Add to your cart and check out. (apply any Coupon Code you may have at this step)
  • An email will come with our thanks and shipping instructions.
  • When we receive your mic, we’ll send you an acknowledgement email and we’ll get right to work on it!
  • Normally within a few days, we will ship your improved modded mic back and you will receive another email with our outbound tracking information and any special notes about your build.

MXL 990 Mod

The 990 is a great mic to rebuild. It is built like a tank mechanically and the result is a mic with a very boutique sound, weight and look. Our special version of the jaSb board is designed specifically to fit in the 990 (or 920). Like the standard board, it also has an optional internal pattern switch. We optionally replace the headbasket with a high quality one from mic-parts.com. That is something you can do yourself at any time too. At this time, the 990 rebuild can only be done as a Transformerless mic.

Other LCD Mic Mods

This is the everything else category. The standard versions of the jaSb transformerless or BFM transformer-coupled boards will fit in most mics from MXL, CAD and others.

Transformerless Models in this group are: MXL 2006, MXL 2008, MXL 910, MXL 990, MXL 870, MXL 550, MXL 440, MXL V250, MXL V63M, Tascam LD-74, MCA SP-1, Nady SCM-800, CAD Audio GXL2200, CAD Audio GXL2400, Scarlett Studio, Other “BM800” Amazon cheap-o mics. Ask about your mic.

These mics can be rebuilt as transformerless with the jaSb board or transformer converted with our BFM board and an adapter board.

SDC “pencil” Mics

Yes, we do SDCs too! Our BFM circuit was originally derived from the Neumann KM84 and adapted for LDC mics. The TFM (T for Tiny) circuit is designed for MXL SDC bodies like the 991, 551, 603 and 840. We offer a choice of transformer and capsule(s).

Sterling Audio ST55 (Groove Tube GT55) Mod

The Sterling Audio ST55 is a fantastic Transformer-Coupled mic to rebuild. The mic features a heavy solid construction and switches for Pad and Hi Pass (low cut) filter. Our BFM-T-55 board is designed for these mics and has an internal pattern switch. We replace the standard Sterling “Resonator Disk” capsule with our standard k47 style capsule. The HP filter switch kicks in at about 135Hz. We have several Transformer options to offer.

Capsule-Only Mods

The Rode NT2 is a well built microphone. The electronics are a nice implementation of the Schoeps circuit designed by Jim Williams with premium components. The Studio Projects C1 also has a decent circuit. The problem with both of these is that they paired a linear circuit with an overly bright k67-style capsule. These mics are very bright and sibilant. We can swap this capsule with one of our k47 style LDCs and make this mic really useful again.