MXL 990 Mods

We have many DIY modification options for the MXL 990. Are you looking for a simple upgrade, or a full rebuild? We have what you need.

Navigating the Options

We have 2 distinct circuit options, and 5 different capsule options listed below. There is no "good/better/best" breakdown here. All of these options yield high-performance microphones. The options differ in sonic color and character.

The transformerless 990 kit has higher sensitivity (higher output), clean/accurate transient response, and low distortion. This is a more "modern" sounding microphone. It's the best choice for voiceover and classical (nylon string) guitar, because those applications prefer high output and clean transient response. For most other sources, you could use either circuit and get great results.

The 990XF kit (the 'XF' is shorthand for 'transformer') has lower sensitivity / lower output, and rich harmonics. It is Cardioid only, with no switchable options. It is easier to build because the parts count is ~50% lower. It has 2 discounted capsule bundle options that are not available elsewhere, making it a lower cost option for a full mic rebuild.

#1: Capsule Replacement

If you've never upgraded a mic before, you might wish to start with something very simple. The mic's capsule gives you 90% of the sound of the microphone. In the case of most inexpensive condensers, the capsule is a $5-$10 part that, frankly, does not sound very good. Our line of premium replacement capsules will re-voice your mic, giving you a much smoother and more musically useful sound. In the case of the 990, a new large-diaphragm capsule will lower the mic's self-noise too. And it can be replaced by soldering just two wires.

If you're keeping the circuit stock, but you want an easy upgrade, we recommend the RK-47. This capsule turns the 990 into a wonderful all-purpose microphone, with great detail in the mids, and a neutral top end -- a welcome contrast to most over-bright condensers. The RK-47 is compatible with the stock 990 circuit, making this a great low-budget solution to improving the microphone.

The RK-12 is another option that works with the stock circuit. This would give the mic a more open top end, but that top end is balanced by a very full low frequency response.

We do not recommend the RK-87 capsule if you are usign the stock circuit, because the stock circuit does not provide the corrective EQ. that the RK-87 capsule prefers. If you wish to use the RK-87 capsule, plan to also install our transformerless circuit kit (see immediately below).

#2: 990 Circuit Replacement Kit

We pioneered the full-circuit replacement option for the MXL 990 in 2012, and we've revised and upgraded the circuit design, the board layout, and the build guide multiple times. The latest revision provides a complete implementation of the Schoeps transformerless circuit, made with handpicked, high-grade components. We've added a switch to the PCB that can be built as either a cardioid/omni pattern switch, or as a 10dB attenuation pad, adding a feature to the mic that was not present in the original.

If you're wondering why you would want to replace MXL's transformerless circuit with the MicParts transformerless circuit, the answer is: our circuit has higher sensitivity, lower noise, lower distortion, and a cleaner / less cluttered signal path. We use a direct coupled topology for the high-impedance input circuit, which itself reduces low-frequency noise and distortion; that's just one of dozens of optimizations that we've implemented that are not found in the mic's original circuit.

Our transformerless circuit also provides optional high-frequency attenuation (EQ) within the circuit, enabling the use of brighter capsules that require in-circuit EQ, such as the RK-87.

Click for more information on our MXL 990 PCB kits.

#3: 990XF Circuit Replacement Kit

The 990XF circuit kit provides a more vintage and saturated tonal option than the transformerless circuit above. This transformer-coupled design, like our best-selling T-84, creates some harmonic content to complement the source.

This circuit is our easiest-to-build large-diaphragm option, with only 20 components on the PCB. (The low parts count is not an indication of sonic compromise, but rather of circuit elegance -- after all, it was good enough for Neumann.)

Some customers have pointed out that the transformerless 990 circuit kit must be "better," because it has more reviews. This perception misses the fact that the transformerless kit was launched 9 years earlier, and was the only circuit upgrade option for that entire time. A more relevant analysis: both kits sold equal numbers in 2022, within 2%. We recommend choosing one based on the desired sound, or ease of build, or in order to distinguish this mic from whatever else you already own.

#4: Custom Headbasket

Our custom, handmade headbaskets for the MXL 990 provide a significant cosmetic upgrade. These are available in two colors, "satin nickel" and "black chrome." Click for more information on replacement grilles for the MXL 990.

Audio comparison to $3200 Neumann U87 Ai*

The "990B" circuit mentioned here was our 2nd major revision and upgrade to the original 990 transformerless circuit; the version being sold today is one or two revisions newer still, but we've dropped the letter suffix in favor of just calling it the "990 circuit kit."

Also worth noting: we're well aware that the U87 does not have a K47 capsule. The coloration differences between these two sample tracks are due to this capsule voicing. The point of this test is not to suggest that putting a K47 into an MXL 990 turns the mic into a U87, but rather to illustrate that an upgraded MXL can match the sound quality of a $3500 commercial microphone.