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Revision 8 as of 2014-03-26 04:54:51

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location: EuroAdapter

x0x-heart pacemaker (Eurorack adapter board)

About the pacemaker

The pacemaker is the shortest path to getting your x0x-heart beating in your modular setup. It pins out all of the knobs, and allows for CV control of frequency, gate, accent, slide, env-mod, decay, and cut-off. There are also switches for waveform select, external oscillators, and both the VCA and VCF outputs are available. The front panel was designed by Grayscale.

Design notes

A few tradeoffs were made in the design of the pacemaker. Most of these were done in hopes of making it easy and inexpensive to build, at the cost of some component fiddling. So, as you build, you can modify your pacemaker to suit your needs.

Assembly tips

You may want to build your pacemaker in the following order, to make it easier to solder.

  1. Solder female 0.1" SIP headers on the x0x-heart.
  2. Place male 0.1" SIP headers into the female headers, and then place the pacemaker onto the other side of the male headers. Now solder them in place. This will ensure accurate alignment between the boards.
  3. Solder remaining components to the bottom of the pacemaker (caps, regulator, and 0.1" DIP header for Eurorack power).
  4. Solder in the LM555 and LM339 (CV to PWM), and associated components. If you have the option, use an LM555 from Fairchild, as the circuit was designed around this. If you do not have one handy, don't worry, any imperfections can be accounted for in the next step. Do NOT solder in the positive input resistor chains at this time.
  5. Solder in 1 channel of input resistors, and verify that the CV to PWM circuit works. It should start making high pulses at 0.5V, and go completely high at 4.5V. If you do not have an oscilloscope to check this with, you can put a high efficiency LED (and 1k resistor) at the output of the LM339. The LED will have no light if there are no pulses. You can reverse the direction of the LED to check for pulses in the other direction. Other methods like using diode peak detectors, or just measuring with a multimeter will probably also work. If your circuit doesn't perform as you would like, adjust the 51k/36k resistor combos to shift the level into the right range.
  6. Solder in the remaining channels once you have verified that the values you have chosen work well. In most cases the default values will be just fine.
  7. Solder in the remaining ICs and passive components.
  8. Solder in the jacks, switches and pots.
  9. Run jumper wires for the remaining headers which do not directly mate to the x0x-heart.
  10. Test to see if everything works. Rinse and repeat.
  11. Wash the flux off the board.

Tuning the x0x-heart after installation

Design files