ASM-2 Construction Guide
ELBY Designs - Laurie Biddulph
9 Follan Close, Kariong, NSW 2250, Australia
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For the choice of wire type and sizes we would suggest:-
7/0.2mm (24AWG – 7/32AWG) for control wires
16/0.2mm (22AWG – 7/30AWG) for power rails (NB: 7/0.2mm is also fine for this
purpose
Single-core screened audio cable for all signal wires
When selecting audio cable, choose the smallest outside diameter possible. I use
10/0.12mm with an OD of 1.6mm. Larger cable OD will result in a larger cable loom. When
connecting screened cable you should only connect one end of the screen to GND. In the
ASM1-Genie this GND connection was provided by running a length of tinned copper wire
around the outside of the pcb. This was achieved by placing eyelets on each corner of the
pcb (using the pcb fixing holes to support the eyelets) and then attaching the wire to the
free end of the eyelets. This approach means that the screen terminations are evenly
spread around the board making it easier to maintain the wiring. The free end of the
screen is cut flush with the end of the outer sleeve of the cable and either shrouded with a
piece of heatshrink or masked by teasing the outer sleeve over the exposed wire.
It is recommended that you treat all semiconductor parts as static-sensitive, especially the
CA3140s (be really careful with these – they are unbelievably easy to blow up).
Component Substitutions and Your Own Modifications:
If you know what you’re doing, go for it. If not, stick with the recommended parts.
TEMPCO’s:
The ASM kits include a TEMPCO resistor for each of the VCO’s. A TEMPCO can also be
used in the VCF but is not included in the kit as this is less critical. The ASM kits provide a
1% metal film resistor for the VCF. The PCB has positions for the TEMPCO on the pcb but
builders are referred to the photo which shows one method for improving the thermal
bonding between the TEMPCO and the MATCHED-NPN. In this approach the TEMPCO is
actually placed directly underneath the MATCED-NPN. Thermal contact is improved
through the application of some heatsink compound.
The current design of the VCO modules requires TEMPCOs with a Positive Temperature
Coefficient (PTC) of 3300ppm. Your VCO module kits will contain one of the following
configurations for this component:-
1. A 3300ppm resistor. In this case resistors R137 and R187 should be replaced with a
wire link
2. A 3500ppm resistor. In this case your kit will also include 2 off 62R 50ppm resistors
which should be fitted in positions R137 and R187
Thermal contact
:
All of the critical exponential converter components are physically placed next to each
other so that they can be in physical contact. The transistors and the TEMPCO resistors (if
used) should, ideally, be thermally bonded together with heatsink compound, for best
thermal results. This is totally optional and only for those who are after perfect
performance.
