An ADSR envelope generator

Envelope Generator from P.E. January 1979

The above diagram shows an envelope generator published as an article in the January 1979 issue of Practical Electronics. At this time synthesiser modules in various forms appeared now and then in electronics magazines - the above design is one of the more straightforward ones, and works very well. Apart from the 741 op-amps, it utilizes two digital circuits - a 4016 quad analog switch and a 4011 quad NAND gate.

The changes that I've written by hand, i.e. R4 changed from 18k to 10k, R5 short-circuited, and IC4 pin 4 connected to -12V instead of 0V were mentioned in the article text when operating the envelope generator on bipolar power supplies instead of the single-ended supply for which the EG was originally designed.

To the right of the dotted line is a simple VCA; I never tried this circuit, as I already had an MC3340-based design which worked well. When I'd tweaked the circuit a bit for the Delta Seven loudness envelope, it looked like this, and the bipolar version for the filter envelope lookes like this. (Note that the power supply connections are not explicitly written in the Delta Seven schematics unless they deviate form the standard +12V/-8V for analog chips and +12V/0V for digital chips. You think -8V is a strange value for the negative supply voltage...? Well, it is, but the circuit should work nicely from +/-12V as well should you want to have a go yourself.)

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