MXL 604 Mods

The MXL 604 is a small-diaphragm condenser with a single combined pad/filter switch. It has detachable capsules; the capsules are compatible  with the 603S and 991, and numerous microphones from other brands.

The circuit suffers from indifferent parts selection, resulting in relatively high noise and harsh transient response. The capsules, like most inexpensive SDC capsules, are hit-and-miss; most exhibit thin bass, a 5dB notch in the upper mids, and a sharp boost above 12kHz.

We recommend replacing the MXL capsule with our custom Cardioid and Omni SDC capsules, which can be installed without tools. We also recommend our Schoeps circuit replacement kit; although it sacrifices the mic's pad/filter switch, the improvements in noise and sound quality are a worthy trade for most users.

SDC Capsules

Our proprietary SDC capsules are available in both Cardioid and Omni varieties. We handcraft and individually test each capsule to meet exacting specifications. We offer matched pairs in both patterns.

The Cardioid capsule is voiced with a relatively flat response, to ensure sonic compatibility with a wide variety of sources. These capsules have been favorably compared to Schoeps SDC capsules costing hundreds of dollars.

Needless to say, these capsules can be screwed onto the MXL 604 without tools. They work nicely with the stock circuit (and they work even better with our custom Schoeps replacement circuit).

Transformerless SDC Circuit Kit

transformerless circuit kit

This circuit kit was designed in-house as a drop-in replacement for the MXL 603S. It fits the MXL 604 also, although does not support the pad/filter switch of the 604. This kit contains a full implementation of the Schoeps CMC5 circuit design.

The circuit kit contains our custom, US-made circuit boards, 1% tolerance audio resistors, Wima film caps, low-noise Panasonic electrolytics, and NOS transistors. They deliver linear frequency response from 20Hz–20kHz, with very low self-noise and distortion.

Read more about the Transformerless SDC Circuit Kit.