Mechanizing A Eurorack Sequencer

Eurorack has taken over the synthesizer community, and hundreds of people are building their own eurorack modules. [Michael Forrest] designed and built his own Eurorack sequencer module that doesn’t use weird things like capacitors and chips to store a signal. Instead, he’s doing it with stepper motors and some clever engineering.

The basic idea of a Eurorack sequencer is to somehow store a series of values and play them back repeatedly. Connect that sequence to a clock, and you get the same pattern of sounds out of your synth. This can be done digitally with a circular buffer, in the analog domain with a bunch of FETs and caps, or in this case, on a piece of paper glued to a stepper motor.

The key bit of mechanism for this build is a stepper motor with 96 steps per rotation. This is important, because the module is controlled by a clock pulse from the sequencer. Since 96 is evenly divisible by 8 and 16, that means this sequencer will play back in 4/4 time. That NEMA 17 motor with 200 steps per resolution simply won’t work in this situation. Rather, it will technically work, but it’ll be unusable.

The electronics for this build are surprisingly simple, with an Arduino taking in the clock pulse and sending the step signals to an H-driver. The motor spins a paper disk, which is read with a photoresistor and a LED. It’s simple enough to be fun, and yes, it is mounted to a proper Eurorack-sized panel. You can check out the video of this build below.

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The Coolest Electronic Toys You’ll See At NAMM

Winter NAMM is the world’s largest trade show for musical instrument makers. It is a gear head’s paradise, filled to the brim with guitars, synths, amps, MIDI controllers, an impossibly loud section filled with drums, ukuleles, and all sorts of electronic noisemakers that generate bleeps and bloops. Think of it as CES, only with products people want to buy. We’re reporting no one has yet stuffed Alexa into a guitar pedal, by the way.

As with all trade shows, the newest gear is out, and it’s full of tech that will make your head spin. NAMM is the expression of an entire industry, and with that comes technical innovation. What was the coolest, newest stuff at NAMM? And what can hackers learn from big industry? There’s some cool stuff here, and a surprising amount we can use.

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Glitch Delays And Teensy Audio

With the release of the Teensy 3.6 and the associated audio processing libraries, it’s never been a better time to get into DIY synth and effects projects. [Scott] is a musician and maker of electronic musical instruments, so he decided to leverage the power of the Teensy and make a delay module that really can’t be done any other way.

The function of this delay module is somewhat similar to a multi-head tape-based delay, only it’s completely impossible outside of the digital domain. There are four ‘read heads’ on a circular buffer. The first three heads play small loops within the buffer at different speeds, one at the original speed, one at half speed (and an octave below) and one at double speed (and an octave above). The fourth head doesn’t loop, instead, it plays the delay buffer in reverse. There are, of course, handy knobs for setting the level of each ‘read head’.

This project is built around [Scott]’s port of the JUCE framework, a very powerful audio API that’s now well suited for laptop and embedded development. The files for this project are all available on the GitHub, and [Scott] plans to build an expansion module for CV control of all the parameters.

So, how does this glitch delay sound? Pretty good. The video below is just a tele into a looper pedal, and into the glitch delay. There are surely some ambient post-rock stars wetting their skinny jeans over this one, and it’s a great application of the Teensy’s audio processing power, to boot.

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Modular Drum Machine Creates Random Rhythms

Don’t worry, the rhythms themselves aren’t random! That would hardly make for a useful drum machine. [kbob]’s creation does have the ability to randomly generate functional rhythms, though, and it’s all done on a breadboard.

The core of this tiny drum machine is two Teensy dev boards. One is an FM synth tuned to sound like drums, and the other is a random rhythm generator with several controls. The algorithms are from Mutable Instruments’ open source Eurorack modules. The entire thing fits on a breadboard with JIGMOD modules for the user interface. The machine runs on lithium batteries in the form of USB cell phone chargers. The battery holders were designed in Fusion 360 and 3D printed.

The function of the drum machine is pretty interesting as well. There are a set of triggers tied to the buttons on the machine. When a button is pressed, the drum machine plays that sound at the appropriate time, ensuring there are no offbeat beats. The potentiometers are polled once every millisecond and the program updates the output as required. There’s also a “grid” of rhythms that are controlled with two other knobs (one to map the X coordinate and the other for the Y) and a “chaos” button which adds an element of randomness to this mapping.

The modular nature of this project would make this a great instrument to add to one’s musical repertoire.It’s easily customizable, and could fit in with any of a number of other synthesizer instruments.

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