Troubleshooting the ASM-1

Problem Solution
VCO won't oscillate Listen to the SawTooth wave form. Check that the FET is properly oriented. Increase capacitor from 18pF to 25 or 30 pF.
Voltage Drop on the power supply
A hot or dis-colored 22 Ohm resistor on the center-line of the board.
Tantalum Capacitor in Noise Section reversed
Distorted output - sounds like a buzz-saw or static Hot input to filter - attenuate the input to +/-2.3V for 2 voices.
Reduce resonance (Q)
Envelope Doesn't Trigger Adjust Envelope Trimmers
Low Output from White Noise Increase gain on noise trimmer.
White Noise Output pops or cuts out Poor performing noise transistor. Test on a breadboard, listen and perhaps view on a scope to see the voltage swing.
Filter doesn't track at ALL Adjust VCF tracking trimmer. Deflux. If that doesn't help, perhaps you have a bad transistor.


A few general construction tips

Buy polystyrene caps for the oscillator (VCO) section.
Buy trimmers with the adjustment screw on top so that the board can be easily adjusted regardless of the mounting orientation.
Add input diodes to the envelopes. GATE SIGNAL -->|-- GATE IN

If you have any ASM-1 construction tips, e-mail me at roytate@ionet.net

Last modified: Saturday, April 04, 1998