Another Damn Envelope Genertor

[gstopp at fibermux.com]

     This time a voltage-controlled linear-slope ADSR....
     
     I guess that once I stumbled across the LM358/74HCT4002 attack/decay 
     flip-flop envelope generator front end, it's just a matter of 
     re-arranging a few wires around the relays or analog switches or 
     whatever to get all kinds of different ADSR's (see I'm using one of 
     those stick-wires-in-the-holes prototyping board thingeys).
     
     Now I've created a linear ADSR with voltage inputs for the four 
     parameters. The time ranges are from 5 milliseconds to about 8 
     seconds, for a CV range of zero to 5 volts. The basic integrator is 
     based on the voltage-controlled slew limiter from Electronotes, using 
     a CA3080 and an op-amp buffer.
     
     A 74HCT4053 triple SPDT analog switch is used. One of the switches is 
     connected to the input of the 3080 to tell it which way to charge, and 
     the other two switches select the various time constant pots that go 
     to the 3080 control. One possible weirdness in the design is the fact 
     that the time constants don't change much until the CV gets down to a 
     fraction of a volt, at which point they rapidly get longer and longer 
     as you get real close to zero. Although this could be compensated for 
     by using non-linear tapered pots, or modifying the CA3080 control 
     drive, it actually may be a good thing to have micro-control of the 
     time constants for short enevlope times.
     
     Once again I built this to run on +5 volts for the 74HCT parts, since 
     I still haven't gone out and bought some 4000-series parts for +15 
     experiments. The 3080 and the output buffer/3080 control chips run off 
     of +/- 15V. I still need to draw up the schematics since it actually 
     takes longer to draw (and write these emails) than it does to whip out 
     the hardware.
     
     - Gene
     gstopp at fibermux.com