External controller module DIY/Kit

Hello, I build eurorack modules as Karltron, and sell them as PCB or kits or assembled. I need to tell you about a device I’ve made for the video-synth community.

Originally I made a box with some knobs to show the kids at MakerFaire that voltages can be manipulated easily, it would take five volts from a battery and attenuate it through some potentiometers, then run that back into a eurorack system to let people get a feel for manipulating audio. Then I became enamored by the external controller as a device to enable easier performance/jamming when your modular is patched full and little knobs get hard to find. Bigger knobs are better for fine adjustments, and segregated play-surface is better for live jamming or sharing with a partner.

Later, at the Milwaukee Synth Meet, I met an LZX user playing a 9U-84HP rack and it was so full of little knobs and cabling, I thought he might be having trouble collaborating with nearby artists, so let’s plug in my controller box. I learned you guys want a one-volt scheme, and I was informed there’s not a lot of one-volt designed devices, and this could be really useful to your community. I reached out to the LZX Facebook group and got some feedback like it should have plus and minus one volt ranges, and faders over pots.

Finally, we have this device made to hopefully suit your performance needs. It takes a 5V USB cable, and returns four 1/8" TS Mono lines in the -1/+1 V range, switchable to 0/1V, bipolar LED indicators. We’ve tested it against an LZX system to ensure the filtered constant control voltage is smooth enough to leave no visible artifacts from the USB power line. Otherwise designed to be cheap, it’s two PCBs and a couple of through-hole LM324s.

I showed it off to the LZX Discord group and they pointed me here to gain the widest audience.

Let me know what you think, thanks.

Little demo video

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