Erica Synths EDU DIY Wavefolder Eurorack Module Kit - Manual (Page 44)

MODULE ASSEMBLY APPENDIX
Before we start building, let’s take a look at the complete mki x es.edu Wavefolder
schematics (see page 3) that were used for the final module’s design and PCB fabrication.
Most components on the production schematics have denominations (a name – like R1, C1,
VT1, VD1, etc.) and values next to them. Denominations help identify each component on the
PCB, which is particularly useful during calibration, modification or troubleshooting.
XS1 and XS2 are the Audio input jack sockets, XS3 is the Audio output jack socket – these
are the very same we’ve already been using on the breadboard for interfacing with other
devices. In our designs, we use eurorack standard 3,5mm jack sockets (part number
WQP-PJ301M-12).
XP1 is a standard eurorack power connector. It’s a 2x5 male pin header with a key (the
black plastic shroud around the pins) to prevent accidental reverse polarity power supply
connection. This is necessary because connecting the power incorrectly will permanently
damage the module.
VD1 and VD2 are schottky diodes that double-secure the reverse polarity power supply
protection. Diodes pass current only in one direction. Because the anode of VD1 is connected
to +12 V on our power header, it’ll only conduct if the connector is plugged in correctly. If a
negative voltage is accidentally applied to the anode of VD2, it closes, and no current passes
through. The same goes for VD2, which is connected to -12 V. Because schottky diodes have
a low forward voltage drop, they are the most efficient choice for applications like this.
Next, we have two 10 Ohm resistors (R2 and R3) on the + and – 12 V rails, with decoupling
(or bypass-) capacitors C1 – C4. These capacitors serve as energy reservoirs that keep the
module’s internal supply voltages stable in case there are any fluctuations in the power
supply of the entire modular system. In combination with R5 and R6, the large 47 microfarad
pair (C1 and C2) compensates for low frequency fluctuations, while C3 and C4 filter out radio
frequencies, high frequency spikes from switching power supplies and quick spikes created
by other modules. Often another component – a ferrite bead – is used instead of a 10 Ohm
resistor and there’s no clear consensus among electronic designers which works best, but
generally for analogue modules that work mostly in the audio frequency range (as opposed
to digital ones that use microcontrollers running at 8 MHz frequencies and above), resistors
are considered to be superior.
Another advantage of 10 Ohm resistors is that they will act like slow “fuses” in case there’s
an accidental short circuit somewhere on the PCB, or an integrated circuit (IC) is inserted
backwards into a DIP socket. The resistor will get hot, begin smoking and finally break the
connection. Even though they aren't really fuses, just having them there as fuse substitutes
is pretty useful - you’d rather lose a cent on a destroyed resistor than a few euros on
destroyed ICs.
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