◊ PCB Documentation

Fourses Tarp

The Fourses Tarp is one of three variations on the Fourses noizy synths, designed by Peter Blasser of Ciat-Lonbarde (the other two are the Fourses Arpserge, and Fourses Tarpterge). All three versions were originally released as paper circuits - builders would print the layout on paper, glue to a piece of cardboard, punch holes for component leads, and then weave and solder the leads of the components together to simulate a printed circuit. This PCB is a translation of that design to an actual printed circuit board, for ease and reliability (at some expense to DIY self-sufficiency). You'll still want to grab Peter's original paper circuit PDF , which includes most of the build documentation you'll need.

Thanks to Peter for his design, and for giving his permission to provide these PCBs.

PCBs are $25.00 @ — ORDER HERE

The Fourses series are "all based on the idea of four oscillators that bounce off of each other, creating animalistic noises". So there's a ring of signal generators, each modifying the other, which under the right conditions approximates chaos. There is a single pot control for each of the oscillator circuits, as well as 40 touch nodes – in practice these internal connections are exposed as touch points. Touching multiple nodes with your fingers (or connecting them with alligator clips / copper scrubbies / chains etc.) makes interconnexions between parts of the circuits, triggering and modifying the sounds, and adding to the chaotic behaviours. The result is a tactile and intuitive playing surface, with built-in indeterminacy. Also, fun.

This PCB also includes a simple onboard amplifier, based on the LM386 chip. To use this as a solo instrument, you'll want to connect the input of the amplifier to one or more of the touch nodes (or to a conductive object you can lay one or more nodes), and then take the output of the amp to listen or further modify. If you have other touch instruments, you can also interconnect the signlals from the touch nodes between devices – just make sure they have a common ground connection between them.

Bill of Materials

Fourses Tarp BOM
QTYPart DescriptionPart Number *
110r Resistor1/8 watt270-10-RC
124.7k Resistor1/8 watt270-4.7K-RC
1610k Resistor1/8 watt270-10K-RC
222k Resistor1/8 watt270-22k-RC
28100k Resistor1/8 watt270-100K-RC
16470k Resistor1/8 watt270-470K-RC
122.2meg Resistor1/8 watt270-2.2m-RC
450k Potentiometer linear1012A-B50K or
11N4001 Diodeblack epoxy, observe polarity band863-1N4001G
4.001 uf Capacitor**MLCC581-SR211C102K
4.01 uf CapacitorMLCC581-SR211C103K
41 uf CapacitorMLCC581-SR211C105K
210 uf Capacitorelectrolytic647-UVZ1J100MDD
1220 uf Capacitorelectrolytic667-ECA-1HM221
12BC549NPN transitor512-BC549BTA
8BC559PNP transitor512-BC559BTA
4IC LM358dual op-amp595-LM358P
4CD4066Bquad analog switch595-CD4066BE
1IC LM386amplifier926-LM386N
58 pin DIL socketfor ic649-DILB8P
414 pin DIL socketfor ic649-DILB14P
4LEDobserve polarity; flat side/short leg = cathode859-LTL-4223

* Mouser.com part numbers, except pots from Smallbear-electronics
** different values here change the frequencies, good place to start with mods.

Additional Build Notes

  • Potentiometers:
    • The potentiometer functions are symmetrical to center – turning clockwise or anti-clockwise has similar but mirror-imaged impact to the sounds produced. So pots can be mounted on either side of the board without rewiring.
    • If pots are mounted to the component side and used to secure the board to the panel, be sure all the components are lying flat enough to they don't bump into the panel.
    • I personally prefer to mount the pots more toward or off the edge of the board, using flying wires rather than board mounting - otherwise, I find them interfering with patching the nodes.
  • The added LM386 amp is entirely optional – I have one of peter's OG fourses, which has two 386 amps to drive a pair of speakers, so I threw one on for convenience. It's not a particularly clean amp, but it's a noisy circuit. The amp schematic is straight from the data sheet, wired for 200x gain. If that is too high (blown out sound, or sound bleeding in when unintended), you can omit the 10uf cap between IC pins 1 and 8 (towards the notch on the IC), which changes the gain to 20x.
  • The first run of boards matches the original paper circuit... there was a resistor with one unconnected end, and I realized that the feedback "circle" of connections between sections wasn't complete, but wasn't sure if it was intentional or an error, so I just left it as an unattached node (marked with a "?", near ampOut). Josh Rodriguez I think subsequently decided it was an error, and published a fix, which you can easily do:

    Quite honestly, I couldn't hear a difference, but I included his fix in the next revision of the board (marked rev1.1). Thanks to both Josh, and Ian Watson, for helping straighten that out.