Open source electronic musical instruments designed in London.
DIY Eurorack Module
DIY random looping sequencer in Eurorack format

Specifications
Supply: 40mA
Size: 10 HP
Depth: 40mm

Documents
Modular Grid
Schematic
Github
License: CC-BY-SA
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Full kits from Thonk

21 things to know about the Turing Machine

  1. This is a binary sequencer, based around a 16 bit memory circuit called a shift register. It’s designed as a sequencer that you can steer in one direction or another, not one that you can program precisely.
  2. You cannot program this sequencer to play specific tunes. You cannot save sequences. You can never go back to a sequence that has changed.
  3. To put it another way: This Random Looping Sequencer is a module that produces clocked randomly changing control voltages. Unlike many random voltage generators, these sequences can be locked into loops that repeat according to the length control.
  4. Despite being hard to explain, since it was launched in June 2012, the Turing Machine has become one of the most popular Eurorack DIY projects. The #turingmachine tag on Instagram contains lots of great demos (and a certain amount of the real Alan Turing).
  5. Turing Machine Expanders connect to the back of the module, and take the sequence from the main module and use it in different ways:
    • Volts adds an extra voltage output, with voltages set by five pots.
    • Pulses sends the sequence into eleven rhythmic pulse-train outputs.
    • Vactrol Mix is the most unusual: a sequencer controlled matrix mixer. It's fantastic, but really hard to explain.
  6. In the Turing Machine, looping is controlled by the big knob.
    • At noon, the sequences are random.
    • At 5 o'clock, it locks into a repeating sequence.
    • At 7 o'clock, it double locks into a repeating sequence twice as long as the 'length' setting.
    • At 3 o'clock or 9 o'clock, it slips; looping but occasionally changing notes.
  7. The original demo video (using the old Mk1 module) is probably the easiest way to understand the concept of a locking and slipping sequencer:
  8. While this 27 minute video from DivKid explains everything you need to know about the Turing Machine and expanders:
  9. You can try out a fully operational Turing Machine + Pulses + Volts in the free VCV Rack software.
  10. The circuit was inspired by the long history of shift register pseudorandom synth circuits, including the Triadex Muse, Buchla 266 Source of Uncertainty and Grant Richter's Noisering.
  11. Musically, the module was inspired by 60s and 70s minimalist process music by people like Steve Reich, Terry Riley or Philip Glass: “I am interested in perceptible processes. I want to be able to hear the process happening throughout the music.To facilitate closely detailed listening a musical process should happen extremely gradually.” Steve Reich, Music as a Gradual Process, 1968.
  12. While designing the Turing Machine, I compiled this Random Reading List which includes notes on the history of random sequence generators from Marvin Minsky's Muse to Don Buchla's Source of Uncertainty to Doepfer's A-149 module.
  13. Like most sequencers, you can also use the Turing Machine like an oscillator - or more accurately a waveshaper. When clocked at audio rates by a square wave oscillator, it creates random wavetables. This video explains:
  14. Tony Surgeon is a long-time Turing Machine user. In this workshop from 2016 he shows how he uses it to generate sequences which are then looped on an Octatrack.
  15. The original design had a backpack PCB to power the expanders. The update in 2016 added a new panel design plus:
    • Rotary loop length switch
    • Pulse out
    • Two boards, includes Backpack circuit to drive expanders (compatible with old Music Thing expanders)
    • Easier to build: a larger PCB in the same width, clock and noise circuits are more robust
    • Noise level trimmer & reduced voltage in noise circuit to make circuit more robust with different noise transistors
  16. Turing Machine is open source, which has inspired many offshoots, alternative panels and third party expanders, including:
  17. Read more about Music Thing Modular and open source.
  18. The Turing Machine is not a real Turing Machine the way Alan Turing explained it. The name is vaguely relevant because the module uses a loop of data being changed, but computer scientists find it very annoying.
  19. The original Mk1 documentation contains more detail about how the Turing Machine works, including a block diagram.
  20. The Turing Machine is a fairly straightforward through-hole DIY build, but it's fairly dense and takes a while to complete, so probably shouldn't be a first DIY project (I always recommend Mikrophonie as a first build). Build documents are available from Thonk. If you get stuck, the Github Issue List is probably the best place to start - remember to check closed issues as well as open ones.
  21. Once you've built the module, don't forget to calibrate it to ensure it locks properly.