Attenuverters are critical to modern modular synthesis and are found in classic modules by Make Noise, Mutable Instruments and the like.

They have been around for a long time; I first saw them used in the late 70's in an instrument called an Oberheim SEM, which is now considered a classic.

I did some research on the attenuverter subcircuit in the SEM and contacted Tom Oberheim directly to gain insight as to why his attenuverter design is so musical and user friendly.

To my astonishment Mr. Oberhiem emailed me back!

At the core of Tom's design is a somewhat unusual component--a Center Tap Pot. This is a potentiometer with the center of the resistive element brought to a 4th solder pin which you can connect to ground.

Fortunately this somewhat unusual part is still readily available from major electronics retailers.

So, here we have a center tap pot attenuverter inspired by the Oberheim SEM, with some extra features, such as voltage control of the output signal's DC offset. It is compliant with the Eurorack standard: 4HP; +/-12V; Skiff depth, and so on.

The module requires 3 PCBs: main board, front panel, and standoff board for the ALPs center tap pot.

if you build this module I suggest making the front panel in black with white silks.

You can get more information from the blog post: https://audiodiwhy.blogspot.com/2022/10/euro-sem-style-attenuverter.html

I include below eagle files, PDFs; a zip of all Gerbers and so on. Note that the main PCB uses 2x SOIC SMD parts (the op amps) but I don't find those too hard to solder--tape them down, use flux and a fine tip on your iron, and be patient. The rest of the components are through hole.

Have fun building!