I’m still playing around with a design for a paraphonic build… 6 oscillators + 6 envelopes + 6 vcas, mixer, envelope + filter.
For the first envelopes, I’m building just the lmnc attack/release envelope generator for each voice, and I’d really like to just have one attack and one release knob on the front panel.
How is this normally achieved? How was it done for things like the Roland Juno?
My understanding is I have a few easy-ish options… the one I’m thinking of is using vactrols as variable resistors in place of the pots, and having pots on the front panel controlling the brightness of the vactrols’ leds wired in parallel. That way I’d have one set of vactrols controlling the attack, one set controlling the release.
One option could be using digital potentiometers and rotary encoders?
Possibly there is some solution using a microcontroller… or adcs… dacs… multiplexers?
Using voltage controlled envelope generators would make this straightforward
Not that cheap though.
For adapting a non VC design I’m skeptical vactrols would work satisfactorily, what you would like is linear control across the 100k–1M range and vactrols aren’t very linear. I’m not so sure you could get them to behave consistently enough as well.
Microcontroller and digital pots sounds more promising, though also not that cheap.
As for the EG itself, the LMNC AD/AR is simple, but its use of a TL072 and diode to truncate the response to positive voltages is kind of sketchy; there are other similar designs using e.g. an LM358 which I think are likely to give better results, e.g. Envelope Circuits: a simple AR design using op amps | synthnerd .
Thanks for your reply. You’re right, the EnvGen would make this problem trivial.
I think I’m going to bite the bullet and grab some of those, they are a bit expensive but I’ve saved some money by avoiding 3340s for each voice and going with the pico dco, and it’ll probably save me some headaches trying to figure out how to do it with a microcontroller.
The 3364 also looks like a great solution for vcas too, I hadn’t seen these before. I was going to go for vactrol gates for each voice but the 3364 would be cheaper, so I can save a little there too.
I tried to build polyphonic filter and envelope out of discrete components and it really gave me a hard time. Besides adding voltage control to the parameters to control them all at once also component tolerances come into play here. That lead to a situation where all voices sounded differently even playing the same note. In the end I opted for AS33xx integrated circuits, eg. GitHub - polykit/adsr-3310-8: Kicad schematics and PCB layout for an 8 channel ADSR based on CEM3310/AS3310
Polyphonic controls are split into 2 categories, common controls and individual.
The EGs would be common, so one control line for attack can connect to all the attack control lines of all of your EG chips, same for release, one control for them all. Usually they are things like ADSR lines, filter cutoff and resonance, EG depth, LFO depth.
Individual controls are usually things like oscillator pitch, filter tracking. Gate or triggers for EG. These are individual lines for each VCO, filter or EG and cannot be shared. Even when in unison mode each line is individual but would send the same voltage.
I dont think there is any difference between paraphonic and polyphonic regards control lines unless you are doing things like octave switching of the oscillators in a paraphonic synth like the monopoly.