Using a pair of LEDs to pass an audio signal!!??!?

 

    Put current through an LED and get light.

    Put light into an LED get current!?!!?? Turns out, YES, you can do that! This silly little circuit works as a kinda gnarly distortion circuit. I tossed it together on an impulse, and it worked much much better than the one other time I tried it.

    If you feel like duplicating my work, be sure to decouple your op amp with a 100uF capacitor, seal the pairs of LEDs in some sort of light-proof substance (heatshrink is amazing for this), and you know what? Probably add a ground-reference resistor from the 2nd op amp + input to ground. Maybe 470K. This circuit had a few volts positive offset, which would make sense since I used a TL074. Or maybe ground the + input and wire the potentiometer as a variable resistor... but make it a 1Megohm potentiometer?

    Just an idea or two.

Synthcard VCF

    Okay, I'm designing my SynthCard PCB, and I need a landing page for people who want to build theirs.

    This is a low-pass VCF based generally on an MS-20 filter. The general idea is that it's got two poles for a nice smooth 12dB response. It uses a dual OTA (LM13700) as the resistive elements, and the built-in buffers. Like the MS-20, the feedback circuit, which gives this filter resonance, uses clipping LEDs to get the characteristic growl of this kind of filter. It's designed to work with 12 volts, but will work okay lower, and just fine up to 30 volts, but thirty volts is higher than the SynthCard standard allows so be careful :D

    Make sure you're putting the TL074 and LM13700 chips in correctly -- they're not facing the same way.

    You can use Thonkiconn-style jacks if you want for Eurorack-style patch cables. There's a little pad right next to each Thonkiconn footprint if you'd rather use pins. You can use SynthCard CornerBricks (print them yourself or get them from me) along with DIP-8 spring-type sockets as a way to pass power along all your SynthCards. Remember, the pins for power go in the "back" of the SynthCard if you're gonna use CornerBricks.

    Okay, shoot me an email or find me wherever to ask questions!

    Huge thanks to Benjie Jiao who created the first SynthCard that I'm aware of. He made a business card that could be built into an oscillator based on the Atari Punk Console. We've worked on a standard, which this design probably complies with LOL

     Hi, I'm Juanito, the guy behind the tiny one-person (me!) synthesizer outfit called Modular for the Masses. My goal with this brand was to enable anybody with a small number of dollars to build themselves a sophisticated modular synthesizer.

    Tin cans, RCA jacks and cables, cheap uncased power supplies (or crazier, a couple power bricks taped together)... I built a large, heavy, sophisticated modular synthesizer out of old pallets, tin cans, reused Ethernet cable, and chips, potentiometers, jacks, LEDs, resistors, caps, Arduinos, switches... all the goodies I could find for Very Cheap on AliExpress.

    For whatever reason, only like two or three other people I know of ever started building tin can synthesizers, so in order to get my creations into the hands of more people, I finally started designing PCBs.

    These PCBs will need to be assembled, right? My favorite modules I've designed have some flexibility in their design, to let the builder create a unique example for themselves.

    So this here is the place where I'll put those build guides. Also, I have a much-neglected Squarespace storefront where you can buy modules from me, but for some reason, search engines have a hard time finding those, and an easier time finding Blogger sites.