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Old-style MXL through-hole PCB.MXL 990 PCB, gutted for Adv Mod.

MXL 990 Mod Kit

Item #990Adv
In Stock

The "Advanced Mod" kit for the MXL 990 has been upgraded and improved: click to see the 990A and 990B PCB kits.

Both PCB mod kits include replacements for every component in the circuit, as well as an internal Cardioid/Omni switch. These kits deliver significant improvements to noise, sensitivity, frequency response, and transient response. The finished mic will go head-to-head with the most expensive mics in your locker.

Product Features

•Audio circuit mod designed by Jim Williams
•Includes matched capacitors and resistors
•Includes selected, pre-biased, low-noise JFET
•Includes full-color, 30-page installation manual
•Choose from four different replacement capsules

Why mod the MXL 990?

The MXL 990 was at one time among the most popular mod platforms on the market.

Compatibility Note:
If your 990 has the new “surface-mount” PCB, you’ll want to see our MXL 990 PCB replacement kits instead. The “Advanced Mod” kit on this page is only compatible with the older 990’s, which were made with leaded or “through hole” components.

The 990’s circuit is based on a design by Schoeps, but built with substandard parts to a very aggressive price point that doesn’t leave any margin for testing or tuning. But these shortcomings in implementation just mean that upgrades are that much more effective.

These kits take all the guesswork out of the mod. We include exactly the components you need, plus a detailed manual that illustrates how to install them. Plus, you can pick from our numerous different large-diaphragm capsules. With these kits, you can custom-build whatever flavor of microphone you need.

MXL 990 Advanced Mod Kit

The Advanced Mod Kit is the latest revision to Jim Williams’ ongoing quest for the highest-possible sound quality from these formerly modest microphones. This mod replaces most of the components in the audio signal path, with super-low-noise, high-resolution parts.

All paired resistors and capacitors in our kits are hand-selected and matched to prevent sonic anomalies in the output signal. We’re using Wima film capacitors, long-life Panasonic electrolytics, Dale metal-film resistors (made in the USA), and hard-to-find transistors from Siliconix and Hitachi. The JFET is preselected to match the bias resistors on the MXL circuit board — something that can’t be said of the 2SK170 JFET installed at the factory.

The Advanced Mod Kit comes with a 34-page, full-color booklet illustrating every step of the mod in detail.

Capsule Choices

We recommend replacing the stock small-diaphragm capsule with one of our large-diaphragm choices.

The RK-47 is the most balanced capsule we make, and is the best first choice for studio applications. It combines great midrange detail with just enough low-end warmth and high-frequency “air” to let you capture beautiful, unhyped tracks without concern about layering them up in a mix.

The RK7 is the darkest, most colored capsule we make. It reaches lower than the RK-47, and rolls off the highs sooner, giving it a characteristic vintage sound. These are great for room mics, sibilant voices, and for thickening up acoustic instruments.

The RK-12 is more open on top — bright, without the peaky and piercing highs sometimes associated with inexpensive condensers. These sound great on intimate vocals, drum overheads, and ambient recordings such as choruses and orchestras.

The RK-67 and RK-87 are our two versions of Neumann’s K67 capsule. We recommend these only for the Advanced mod kit, which offers the option of corrective high-frequency EQ required by the K67 design. The RK-67 is a very traditional K67 voicing, while the RK-87 has a slightly sweeter top end, and quicker transient response. Think of the RK-87 as a modern K67. If you love the sound of the U87, one of these capsules (with our K67 EQ change) is the way to go.

About the graphs: The above frequency charts were measured using a 4-way matched set of MXL 990’s, modified with our Advanced circuit mod. The RK-87 mic had different EQ capacitors to take some of the harshness out of the high end, and the RK-12 mic had a 3-layer (stock) headbasket rather than a single-layer basket. The RK-12 and RK-87 are fairly similar, although the RK-12 has a fuller low end and a slightly broader, slightly lower amplitude presence peak than the corrected RK-87.