990XF Circuit Kit

$ 169.00

The 990XF is an adaptation of an old Neumann microphone circuit, designed to fit the MXL 990. This kit replaces the entire circuit of the donor mic; the new circuit provides harmonic content, moderately high output, and low noise.

Pair it with our RK-47C or upcoming RK-67C capsules (see bundle options below) for a complete signal-path upgrade for the 990.

In the kit

The 990XF includes our custom PCB, 100% of the circuit components needed to complete the build, and full-color, step-by-step instructions.

We strongly recommend replacing the 990 capsule. We have created two capsule options that can be bundled with this circuit kit at a discounted price.

This kit does not include the mic chassis, grille, or body ; it was designed to be installed into an MXL 990. If you are buying a donor mic specifically for this build, you can buy a dead / broken microphone, because the circuit and capsule bundles on this page replace 100% of the signal path of the mic.

If your donor mic's grille is mashed, we sell upgraded grilles in two colors.


Capsule Options

In an effort to deliver more sonic diversity to your mic collection, we have developed two new capsule choices. Both are being introduced as inexpensive bundle options with the 990XF circuit kit.

The RK-47C is a fixed Cardioid K47 style capsule: true single brass backplate, 34mm diameter. Within the 990XF, it is within 1dB of having a flat response from 1kHz to 8kHz, then begins a mild rolloff. It is neutrally voiced, with a slightly dark, vintage-sounding top end. This capsule works very well on sibilant voices, bright or jangly acoustic guitars, guitar cab, and drum room. This would make a great broadcast/podcast/VO mic too: solid frequency response through the vocal range, with a bit of compression and saturation from the circuit, and a roll-off in the highs where mouth sounds and fan noise would be.

The RK-67C is a fixed Cardioid K67 style capsule, with two 34mm brass backplates. The capsule itself has a nominally flat response. Within the 990XF, it is slightly scooped (~1.5dB) in the upper mids (4-7kHz) due to the acoustic properties of the 990 body. It has a very mild presence boost (+1dB) at 10kHz. We designed this capsule to be used without high-frequency de-emphasis or correction, so it works very nicely with the 990XF. Within this mic, the RK-67C sounds more "hifi" than the RK-47C, with more air above 12kHz. We like this capsule on drum overheads, bass guitars, large-body acoustics, and strings.

The RK-47 and RK-12 provide alternative voicings to both of these options, with the RK-47 being more mid-forward and brighter than the RK-47C, and the RK-12 being fuller in the lows and brighter in the highs.

The 990XF circuit could be used with the stock 990 capsule, but we do not recommend it. All the large diaphragm capsule options on this site will provide a smoother frequency response.



The new circuit is believed to fit all MXL 990 chassis.

13mm Standoffs

The most common version of the 990 chassis uses 13mm standoffs. (The "standoff" is the plastic or metal cylinder that holds the PCB away from the underside of the capsule deck; the mounting screws go through the PCB, through the standoff, into the threaded holes in the capsule deck.) For these mics, the 990XF circuit board is installed with components on the capsule side of the PCB.

7mm Standoffs

A small percentage of 990 mics uses shorter standoffs, approximately 7mm in length. In these mics, the 990XF board is installed upside down, with the components on the XLR side of the board.

For these installations, solder the capsule backplate wire to the bottom of the input terminal pin, which protrudes through the PCB. It is not necessary or recommended to route the wire around the outside edge of the PCB to solder it to the top of the terminal pin, as pictured in the build guide. Instead, solder the wire to the bottom section of the pin.  We will update the build guide with this tip for the next printing.

990S / 770 / USB - Not compatible

This circuit will not work with the model "990S" (which has pad and filter switches).

This circuit will not work with the MXL 770, although the TL3 kit will.

This circuit will not work with the "990 USB."


Difficulty Level

This is the easiest-to-build large-diaphragm kit we make. The T-25 is slightly easier. The T-12 and T-47 would be more difficult.

See a full list of DIY microphone projects ranked by difficulty in FAQ #2.

Find a complete 990XF build tutorial video on the Video Tutorials page.

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