Open source electronic musical instruments designed in London.
DIY Eurorack Module

Supply: 40mA
Size: 4 HP
Depth: 25mm

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

12 things to know about the Startup mixer, clock & headphone amp

  1. Startup is designed to be the best way to start a small Eurorack case. It does three things. It's a 5 channel output mixer, with a spare channel for stereo signals (like a Korg Volca or a phone). It's a nice clean headphone amp with two outputs. And it's a useful tap-tempo clock, with a second channel giving divided or multiplied clocks.
  2. The best way to understand Startup with with the Quick Start Manual. Although there's not really much to it.
  3. The mixer is unusual because it has no knobs. Instead, relative volumes are set by patching. The top row of inputs are loudest. The second row are quieter, and the single mono input on the third row is quieter still. It's designed to allow a raw oscillator square wave to be patched alongside a quieter-sounding sine wave, or complex output from a Radio Music module.
  4. When a signal is patched into a right hand input, it is mono - placed in the centre of the stereo image. But if anything is patched into the left hand input, the signal splits into stereo. It's not hard left/right split but more like a 10 o'clock / 2 o'clock spread, which should sound more musical in most cases (you can hear an example of the stereo spread in the Phase instagram clip below).
  5. Mixing-by-patching is a different discipline from mixing-by-turning-knobs. Because fine volume adjustments are impossible, use other techniques to balance the mix: Open or close a filter, tweak the resonance. Change the envelope to make a sound longer or shorter. Choose a different waveform. Change the octave range. Add or remove reverb. There are endless possibilities. I've found it a good way to mix by ear, rather than by eye.
  6. One of the inspirations behind the module was this ancient interview with Scottish folk band Aberfeldy which describes recording an entire band album acoustically with one microphone, where the band had to mix as they recorded by moving around the room.
  7. The headphone amp is a powerful, low-noise amplifier with a good quality OPA2134 op amp chip, based on the well known Cmoy circuit, but with the advantage of running on +/-12v rather than a 9v battery. It should be able to drive any headphones with ease, and can also be used as a line out. The outputs share one amp so expect some volume drop or other odd-ness when using two headphones. Please be VERY CAREFUL with volume levels when using headphones with modular synths, which can produce unpredictable signals.
  8. The clock takes a few minutes to get used to. Again, the PDF Quick Start Manual is the best place to start. Tap the left-hand button to set a tempo. It just needs two taps to set the tempo. The Mode light comes on (or off) while tap tempo is ‘listening’. The fastest rate is as fast as you can tap, and the slowest rate is one pulse every three seconds.
  9. The Diviply output produces a clock related to the main tap clock. Tap the (right hand) button to select a faster division (or multiplication), hold to select a slower clock. The 'Mode' light will blink when the division changes. You can see this in action in this Instagram clip:
  10. The clock divider has two modes: When the the mode light is off, clocks coming out from Diviply are Even; ratios of 2,4,8,16. When the light is on, they are odd; 1, 3, 6. Switch modes by holding 'Tap'.
  11. Instead of the longest 'odd' divisions there is a kind of Easter Egg - four Phase modes. Here the Diviply output lags behind the Tap output, catching up every 8, 16, 48 or 96 pulses (in other words, Diviply sends 7 pulses in the time Tap sends 8 pulses, and so on). The details are in the PDF. This Instagram clip shows a pattern that syncs every 8 steps, with a stereo output being driven by two Radio Musics:
  12. Startup is supplied as a pre-populated PCB with surface mount components, with a kit of thru-hole parts. It's a dense board (LOTS of sockets) but is a satisfying, quick build. It's not ideal as a first build (unlike Mikrophonie) but we've successfully had first-time solderers build the module at workshops.