Erica Synths EDU DIY EG Eurorack Module Kit - Manual (Page 40)

Before we start building, let’s take a look at the complete mki x es.edu Envelope sche-
matics (see next page) 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 is the Gate input jack socket, XS2 is the envelope signal output jack socket and XS3
is the inverted envelope signal 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.
VD2 and VD3 are schottky diodes that double-secure the reverse polarity power supply
protection. Diodes pass current only in one direction. Because the anode of VD2 is con-
nected to +12 V on our power header, it’ll only conduct if the connector is plugged in cor-
rectly. If a negative voltage is accidentally applied to the anode of VD2, it closes, and no
current passes through. The same goes for VD3, 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 ( R5 and R6 ) on the + and – 12 V rails, with decou-
pling (or bypass -) capacitors C2 – C5 . 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 (C2 and C3) compensates for low frequency fluctuations, while C4 and C5
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 .
40
MODULE ASSEMBLY APPENDIX