ASM-2 Construction Guide
ELBY Designs - Laurie Biddulph
9 Follan Close, Kariong, NSW 2250, Australia
6 of 19
VCO - Voltage Controlled Oscillator
TEMPCO
For optimum performance the VCO uses a
temperature compensation circuit that utilises a
TEMPCO resistor. For best results the
TEMPCO should be thermally bonded to the
matched transistor pair Q101/Q151. The picture
to the right shows how the TEMPCO should be
mounted. If desired, thermal bonding can be
improved further by the addition of some
heatsink compound.
Assembly Modifications
R106 on the PCB should be replaced with a wire link. R106 and an additional 100K 0.1%
resistor (XR106) will then be wired in series with S110 [KCV] and S101 [TRANSPOSE] on
the panel.
R156 on the PCB should be replaced with a wire link. R156 and an additional 100K 0.1%
resistor (XR149) will then be wired in series with S160 [KCV] and S151 [TRANSPOSE] on
the panel.
R110 on the PCB should be replaced with a wire link. R110 and an additional 100K
resistor (XR149) will then be wired in series with pots P117 [PWM1] and P119 [PWM2] on
the panel.
A significant improvement in the quality of the Sawtooth output (and hence the Triangle
and Sine) can be achieved by performing this modification to U101 and U151.
1. Cut the leg at the shoulder, of pin 4 of the 8-pin wire-
wrap socket for U101/U151 - see image at left
2. Use a small piece of wire offcut and solder a bridge
between pin 3 and the shortened pin 4 - see image at
right
3. Install the socket on to the pcb ensuring that there is a
small gap between pin 4 of the socket and the pcb
