Shared Projects by LMI-DIY

This pcb is for the LMI DIY Transformer box project. This board utilizes 2 LMI10 transformers, using a special internal balanced circuit that extends transformer bandwidth while offering gorgeous tone and character.

This board will work for a mono channel. You will need 2 boards and 4 transformers to make a stereo set.

This PCB also features an optional chassis ground connection and an optional T attenuator output level control. This attenuator allows you to drive the transformer harder while dropping the output level so that the next device won’t be clipped.

A great use for this design is with a set of converters where the user is looking for extra tone and vibe on their mixbuss or the output of a drum machine that needs some extra oomph.

There are only 6 total components per project, 2 LMI10 transformers, 2 resistors and 2 capacitors. The bill of materials (BOM) has links for all the necessary parts.

A standard 10KB potentiometer that can be wired is all that is needed to attenuate the output level.

All solder pads for wires use larger hole diameters and pads for ease of soldering. Ground pours are on both sides of the PCB with large thermal reliefs for ease of soldering to ground pads.

2 M3/#4-40 holes are available for mounting. These pcbs are small enough to install into a small enclosure that is at least 4 x4 x 4. Allow some space for jacks and controls.

BOM: https://docs.google.com/spreadsheets/d/1M-N4P-SpkIswmtWpCIupFmdYMQl_-m3DdI2L2ANYfMg/edit?usp=sharing

Reverb link for LMI10 transformers: https://reverb.com/item/91690905-lmi-lmi10-1-1-transformer-2025-black

Public schematic link (no sharing without attribution to the original author - Langston Masingale)

https://drive.google.com/file/d/1Y2bsHxwlzmSefklms3YLpkL84xclh-Yr/view?usp=sharing

Thanks -L.

This PCB allows the end user to install the D Shell style XLRs commonly found on Amazon, ebay, aliexpress onto a small PCB adapter. This pcb removes the need for wiring individual XLR pins and instead allows you to solder the XLR jack on pads. Each pad is then routed to a large solder pad where you can solder in your wire leads. Each pad is labeled. Chassis GND (optional) is available via the shell tab. You can wire directly to XLR PIN1 from here or utilize various grounding schemes for a DI box (this is already addressed in the LMI DIY DI PCB), microphone preamp, line output, direct out.

This pcb features a full copper pour for Ground (improves shielding from noise) and utilizes larger thermal reliefs for ease of soldering.

This board is confirmed with Male Jack 3 Pin - Panel Mount Jacks D Series Size XLR-M - as found on Amazon or similar XLR male connectors. This board is not directly compatible with XLR female connectors.

This pcb design allows the end user to adapt the plastic TS jacks you can find on Amazon, Ebay, Aliexpress, Tayda and Jameco to a PCB adapter for easier installation and mounting. These jacks feature plastic insulation that separates the Tip from the Sleeve for less problems during installation. Normally they can be difficult to solder wire to, but this PCB removes the hassle and let’s you get back to enjoying your DIY projects!

This PCB is confirmed compatible with PJ-629HAN style jacks and offers a tight flush fitment, which conserves space (because the jacks are longer than traditional TS jacks).

2 large pads labeled TIP and SLV are provided for you to wire in your connections. Orient the jack based on the silkscreen and you should have very little difficulty installing these. A copper pour for ground is provided with large thermal reliefs to ease soldering to the ground pins and ground pad.

LMI DIY DI BOX PCB. This project uses an LMI 50600BRN transformer, which is modeled after the vintage transformers used in the classic Motor City and West Coast direct boxes. This DI box has massive character and “tone for days.”

Features a built-in special ground scheme as used in the Motor City Big Block DI, with the option to add a ground lift switch that shorts XLR pin 1 directly to ground, using the G and P1 pads.

This DI will work well with guitar, bass, keyboards and drum machines. The transformer is strapped for 12..5k to 600 ohms.

All components are labeled ((1) .1uF 50V ceramic capacitor and (1) 51 ohm ¼ watt resistor. Both the TS input and the XLR output solder pads are oversized and easy to solder wires to. Any enclosure that’s at least 2 inches tall, 3 inches wide and 5 inches long should work. There are plenty of options on Amazon that can work for this application. 2 mounting holes (M3, will also fit #4-40 screws) are provided for mounting to a chassis.

This pcb is designed to allow you the freedom to use your own choice of XLR and TS connectors. You select your XLR and TRS connector style, then wire your connections, attach them to the chassis and then solder to the respective pins on the PCB.

To complete your project, you will need to obtain an LMI 50600BRN transformer.

Please purchase the LMI50600BRN here on the LMI Reverb Account. https://reverb.com/item/55811395-lmi-lmi50600-2025

BOM here: https://docs.google.com/spreadsheets/d/14vAdzhV3EEVIOffHBeNZ8IWbqsLcJyjiV8buVmBmESw/edit?usp=sharing