Random*Source SERGE NCOM User manual

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Serge ÷N COM
SERGE
Divide by N Comparator
(÷N COM)
The ÷N COM is a rare, much sought-after and very essential Serge module covering a number of functions:
comparator, voltage-controlled pulse divider, and voltage-controlled staircase generator.
The Random*Source version of the Serge ÷N COM consists of a main pcb and a matching component pcb
serving as an interface to the front panel.
Main pcb (v 1.03) and panel pcb:
Please note:
• The pcb provides for a precision voltage source that should be set up (using the trimmer) so that
the CMOS parts are run on a (stabilized) exact voltage (around 5.116V) - as Serge explains:
“One of the features of the NCOM is its adherence to the 1V octave rule, which permits directly
plugging the staircase out into a VCO and getting a whole tone scale.”
• The pcb uses a precision voltage source against changes and ripple in the supply voltages.
• The component pcb contains footprints so that that pots can be inserted to work in either direc-
tion (“normal” and “reverse”), “normal” should give the expected pot behavior.
• Earlier versions of the pcbs contain some errors and are not recommended to be
used. Please contact R*S about a replacement in case you have a version < 1.03!
• Big thanks to Phisynth and Guy D.!
• Board is designed to be powered by a +/-12V stabilized PSU only. (+/-15V is untested).

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Serge ÷N COM
Bill of Materials
The following values are suggestions and may deviate from other / older versions of the ÷N COM: - this is DIY!
Resistors (1%)
2 10R F1, F2 alt: FERRIT BEAD
2 OMIT R2, R18 * do not install *
1 330R RS R26 - marked "RS" install 330R + 100R trimpot for the 5.15 voltage source
3 330R R25, R31, RS
2 2k2 R1, R9
1 15k R16
2 33k R11, R27 alt: 10k + Zener Diodes (see below)
4 47k R4, R6, R7, R8
2 51k1 (47k) R13, R15
1 110k R5
1 121k (110k) R14
7 249k R3, R10, R12, R21, R22, R23, R24 1% or better - ideally closely matched
1 499k R20 1% or better
1 1M R19
1 6M8 R17
1 100R TS (Precision Voltage) Trimpot (Bourns 3362P or anything that matches the
footprint) to adjust the Voltage to 5.156V - or any value
that yields the desired 1V/Oct scaling of the stepped output
(tune sending the stepped output into the 1V/Oct input of
an oscillator). Use a good DMM and measure between the
two test pads (“- TEST -”).
Capacitors
147p* C* Use larger value e.g. 1nF, I used 220p which
seems to work nicely, too.
9 100n C3, C4, C5, C6, C7, C8, C9, C10, C11 Bypass caps
2 10uF C1, C2 Electrolytic (or 22uF) >= 25V, 2.5mm ls
ICs
2 4559 U2, U5 NJM4559D or RC4559P
2 2N3904 Q1, Q2 NPN Transistor
1 CD4093BE U1 Quad 2-input NAND schmitt trigger
1 CD4520BE U4 Dual binary up COUNTER
1 LM317LZ U6 Positive VOLTAGE REGULATOR
1 LT1009C U7 Precision Shunt
2 ZENER 4.7V D1, D2 Optional: Zener Diodes as CMOS input protection
Install “4V7” if you use 10k for R11, R27.

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Serge ÷N COM
Misc
1 MTA-156 MTA-156 power connector
1
1
SIL header 8pol
SIL header 5pol
pin connectors, linking main pcb to component
pcb - using precision strips allows to break off
pieces as needed
3 Banana Jacks COMP_OUT_A, OUT_F, OUT_J (red) Emerson-Johnson
Mouser: 530-108-0902-1 (red) or Thonk
3 Banana Jacks CV / unipolar (blue or white)
IN-_D, IN+_B, VC_IN_G
Emerson-Johnson
Thonk / Mouser: 530-108-0910-1 (blue),
530-108-0901-1 (white)
2 Potentionmeter
50k
linear (B50K or B100K) Alpha 9mm vertical pcb mount
available from Thonk, Tayda, Mouser ...
Building
This is simply a suggestion - you might nd a different workow more practical:
1. Mount the Banana jacks onto the front panel.
2. Use a side-cutter to separate main pcb and component pcb.
3. Mount the pots onto the component pcb. Pots should sit on the side facing the front panel (as
marked on the board). Don‘t solder them in yet.
4. Carefully mount the component pcb (with the pots inserted) onto the front panel. You may then
have to wiggle each pot a bit to get the pots through. Make sure the threads of the pots go
through completely and the pots sit right at the front panel. You can even screw the pots to the
panel to make sure of that, but you will have to unscrew them again later.
5. Once everything is nicely in place, solder the pots onto the component pcb (while the front panel
is attached). DO NOT SOLDER THE BANANA JACKS YET!
6. Stuff the main board, beginning with the resistors, then caps etc.
7. Main pcb and component pcb are to be connected through precision DIP socket and pins. It is
recommended to use the pins on the main pcb (facing down, soldered from above) and the pin
sockets on the component pcb (standing up, soldered from the front panel side). Break or cut off
the pieces you need and stick them together so that main pcb and component pcb form a nice
sandwich (don‘t solder yet). Check that you didn‘t leave out any pins / holes and that the sockets
are all on the same side (component pcb). Solder all the pins in while keeping the sandwich
together - this avoids any misalignments.
8. Carefully separate the sandwich - if you used precision sockets, this may not to too easy - they
stick together nicely (giving a good connection).

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Serge ÷N COM
9. Mount the component pcb onto the front panel again and screw on the pots from the front side.
10. Make sure everything is in place.
11. Solder the banana jacks in. You can either solder them directly to the surrounding vias (i.e. the
ring around) or - which makes removing easier should you ever need to do that - by inserting a stiff
(bare) wire into the little hole (via) and solder that wire to the top of the banana jack:
12. Attach any screws / spacers if desired and mount the main pcb onto the component pcb.
13. Connect a power cord supplying +12V, GND, GND, -12V to the MTA-header on the main board and
you should be ready to go :-)
Calibration
Using TS, the voltage for the CMOS parts can be adjusted to precisely. The theoretical value should be
5.155V, however, I found that 5.115V worked best in my case. Use a good digital multimeter and measure the
voltage between the 2 test pads (next to the 4520 IC, marked “ - TEST -” and adjust the trimmer. You can also
run the stepped output into the 1V/Oct input of a VCO and adjust the trimmer so that the pitch of the oscillator
stepping up stays in tune.
(Version 01 June 2016)
SERGE Modular by Random*Source. Module and circuit under license from Serge Tcherepnin. All rights reserved.