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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 / mods

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 (All pot headers, J2, J7, J8). Be sure to keep them well aligned and vertical.
  2. Place male 0.1" SIP headers into the female headers (same as above), 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 (U6, C10, C11, J0).
  4. Solder in the CV to PWM components (U3, U2, C1, C2, C4, C8, C13 (C13 might need to be laid flat), R1 - R10.). 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.
  5. Solder in the ENVMOD channel of input components (D1, R11, R12, R35, R39).
  6. Check that the ENVMOD PWM works adequately. Apply power at J0, and check U6 with a multimeter: 1 pin should be 12V, the middle pin 0V, and the other pin 5V. Next, apply a CV to the ENVMOD input (you can solder on the 1/8" jack if it makes it easier). Monitor the voltage output of J3-pin6 (labeled pin3 on the schematic / pin6 on the silkscreen) as you sweep the CV in from 0V to 5V. The PWM out should go from 0% to 100% (the actual design is 0.5V to 4.5V, so anything around there is fine). If you do not have an oscilloscope to watch the PWM waveform, you can put your multimeter on the output, and see when it starts changing. it will be around 0.2V at the beginning, and this will start increasing when the PWM goes above 0%. it will then top out at 4.9V when it hits 100%.
  7. If your PWM doesn't match this, the R35/R39 pair will need a bit of tweaking. If the PWM comes on too early, then it needs to be shifted down by reducing R35. If it comes on too late, then it needs to be shifted up by reducing R39. If any adjustment is needed, it will be small (for example, adjusting R39 from 51k to 47k).
  8. 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.
  9. Solder in the remaining ICs and passive components.
  10. Place the jacks, switches and pots, and attach the faceplate. Then solder the jacks and such in. This will ensure that they are perfectly aligned.
  11. Run jumper wires for the remaining headers which do not directly mate to the x0x-heart. The header pins are labelled with J(N), and match the x0x-heart board. The pin numbers on the pacemaker match the pins they go to on the x0x-heart. Be very careful with J1, as the pin assignments go from left to right, and then top to bottom, and NOT counter-clockwise as a typical DIP component would. See the images below if you are not sure.
  12. Test to see if everything works. Rinse and repeat.
  13. Wash the flux off the board.

Tuning the x0x-heart after installation

Since the components on the x0x-heart are facing the pacemaker, it is impossible to tune the x0x-heart when assembled. So, to tune, disconnect the board, but leave jumper wires in place. Next, run jumper wires from the TUNE pot header on the pacemaker to the TUNE header on the x0x-heart. Now you can tune it as described in the x0x-heart manual. You will need to probe at J6 - pin1 for the VCO output.

Assembly images (hopefully better ones coming soon)

pacemaker_top.jpg pacemaker_top2.jpg pacemaker_side.jpg pacemaker_back.jpg pacemaker_back2_label.jpg pacemaker_back3.jpg pacemaker_back4.jpg

Design files

Through Hole board

The Mouser cart has the minimum quantites to do a single build (minus the pots/jacks/switches). It does NOT include IC sockets, so be sure to pick these up if you need them. The price break on the resistors is at 200, if you want to pick up a whole bag. And i would reccomend getting at least 2 of the 0.1" male SIP header, as it often breaks at the wrong point, giving a useless length.

Surface Mount board

EuroAdapter (last edited 2016-09-23 17:59:49 by guest)