TL3 Circuit Kit

$ 209.00

Style: Transformerless
Distortion: Low
Noise: Low
Character: Neutral
Sensitivity: High
Frequency Response: Flat, with optional high-frequency corrective EQ
Polar Patterns: 3 (Cardioid, Omni, Figure 8)
Pad: Yes, 10dB

The TL3 is our next-generation implementation of the transformerless design pioneered by Schoeps. Once built, it will deliver performance specifications as good as almost any commercial microphone on the market, and better than most.

We designed this circuit kit to fit our new S3 microphone kits. But it also fits two inexpensive "donor" microphones:

  • MXL 770 (but see the "Compatibility update" section below)
  • Monoprice 600800 (but see the "Compatibility update" section below)

The TL3 differs from our existing transformerless circuit kits in three significant ways:

  1. It has 3 polar patterns
  2. It has 2 external switches
  3. The high-frequency EQ can be easily adjusted without soldering

Features & Benefits

  • High sensitivity, low noise, low distortion, ultra-pristine signal path
  • Three-way pattern switch: Omni, Cardioid, Figure-8
  • Switchable -10dB pad
  • Includes pre-biased NOS JFET for maximum headroom
  • User-adjustable high-frequency EQ allows easy voicing

Capsule Compatibility

We designed the TL3 circuit to work with all of our RK series capsules, which offer proven performance, accessories designed to ease installation, and fast email tech support.

High-frequency corrective EQ is supported in the TL3 circuit via a socketed EQ capacitor. This allows you to fine-tune the mic's high frequency response without soldering. A variety of EQ capacitors is included with each TL3 circuit, enabling compatibility with the RK-47, RK-12, and RK-87 capsules.

(We caution mic builders against buying cheap "crapsules" sold on Ebay/Reverb or 3rd party websites -- especially those fraudulently claiming to be MicParts RK-series capsules. We have tested many of those capsules and found significant problems with sensitivity, noise, and especially frequency response, such as thin bass and inexplicable midrange peaks. There are no mic circuits that will make a bad capsule into a great microphone. Therefore, knockoff capsules such as counterfeit RK series sold by third parties will likely cripple your DIY microphone.)


Bundle Discount Option

For a limited time, get a $50 discount on the LDC capsule of your choice via our LDC Bundle Discount plan.

Circuit Kit vs Microphone Kit

This circuit kit is alternatively sold as part of an all-inclusive microphone kit. See the S3 Series. The S3 kits include the mic body, shockmount, upgraded grille, the correct switch markings on the body, and a plastic storage case.


Included with this Circuit kit

  • Two-piece "TL3" PCB set.
  • 100% of components needed to complete the circuit, including 1% tolerance, low-noise resistors, pre-biased NOS JFET, and polyproyplene signal capacitors
  • Full-color, step-by-step installation guide (often described by customers as "the best DIY audio project manual on the market")
  • Tech support via email


These circuit boards will fit the MXL 770 and Monoprice 600800. They will not fit the MXL 990, nor the 990S, nor any other microphone.

Why did we choose the 770 and 600800 as the donor mics for this circuit kit? Because both models have two external switches. The original mic provides a pad and a high-pass filter. We retain the pad, but repurpose the HPF switch as a 3-way pattern switch (Omni/Cardioid/Fig8). (You will want to mark the new pattern switch positions on the body: from left to right the order is Omni, Cardioid, Fig8.)

To purchase the TL3 circuit with an upgraded mic body and capsule, see our S3 series microphone kits.

Compatibility Update - 2022-06

The TL3 circuit was designed to fit a MXL's 4-piece assembled frame, in which the chassis side rails are screwed into the capsule deck and XLR housing. See the photo at right. With one single exception, every MXL 770 and Monoprice 600800 we've seen uses this sort of chassis.

The one exception uses a one-piece cast frame. The assembled TL3 boards mostly fit this chassis, but will require minor filing to provide clearance for one or two components. A small metal file or Dremel tool will correct this minor incompatibility.


Grille Upgrade

If you are using the TL3 to upgrade your own mic, see also our M49 style grilles for MXL 770.

Skill Level

This is an intermediate level kit, similar to our other transformerless circuit kits. It is harder to build than the T-84, but easier than the Fox 460 tube kit.

If you have built one of our microphone kits before, you should have no problems with this one. If you have never built a microphone before, we recommend starting with something easier, such as a capsule upgrade, or the C1/C3 circuit mod kits.

See a full listing of our DIY microphone kits, ordered by difficulty, in the FAQ.

If you have never soldered before, please do not purchase this kit. You must be able to reliably form sound solder joints, or you'll be wasting your time and money.

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