I started this project with the intend to modify a schematic from Moritz Klein to have Release CV. Than I discovered I can extend what I was doing to make it have distinct Decay also, and not control the Decay with the Release Control like the Original. I also made a couple more changes to the schematic, including an option for Release accent trigger. Having these functions was nice, but the module started to be a bit more complicated for my taste, so I created 3 version with increasing complexity. The simplest one uses one TL074 chip and only has ADSR control. The other 2 have different options for CV.
Here is a video for the project:
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look at how compact that is!
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Here is a simulation for the simple version:
https://tinyurl.com/2r3kxjl8
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Interesting variation on the ADSR circuit.
The compromise of not having a state storing element or end of attack detection circuit here seems to be a fixed attack phase duration determined by the duration of the pulse created by the 1uF capacitor and 10K resistor.
This prevents long attacks and very short attacks.
Some control of the duration of the attack phase could be obtained by replacing the 100K and 20K voltage divider by a potentiometer for the second comparator. Maybe combined with an increase in size of those capacitor and resistor.
Unrelated question: the 1K resistor at the opamp’s non-inverting input does not seem to serve any purpose, does it?
Thats right, the attack time cannot be controlled with this schematic. Only the slope of the attack. It’s a tough sacrifice, but the schematic is quite simple. I thought I could add a potentiometer inplace of the 10k resistor after the 1uF capacitor , to allow for variable attack time, but then you would need to have 2 potentiometer adjustments for the attack. Here I made a version, where there is a detection for peak attack voltage:https://tinyurl.com/2epf748p . It’s a combination of schmatics from kassutronics and schmitz bitz. It uses transistors instead of logic gates. I haven’t tried it, but I think it should work fine. Although it’s getting a bit too complicated, and at this point, the Fastest Envelope on the West is looking like the best ADSR I have found so far.
Is there an advantage to that?
I’ve been pleased with the Kassutronics design, to which I added retriggering and looping. For many applications the Schmitz/Yusynth/etc. designs’ slowness in reaching 0 V (or the sustain level) is not a significant problem but for when it is, the Kassu’s precision rectifiers work very nicely.
You sometimes see such a resistor to provide some current limiting protection in the event of an overvoltage input, but that’s not relevant here…
Yeah, the advantage is that transistors are cool and logic gates are boring :D. Also I have tons of transistors and zero logic gate chips. The 1k resistors can be skipped yeah, I don’t think it’s a problem to be there but there is no particular need. I gotta try this version https://tinyurl.com/2z34wg7z . With a stereo potentiometer on the attack, you can adjust both the time and the slope. It looks promissing and you will have full ADSR capabilities with only one quad opamp.
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Haha, yes that’s why I’m on this forum after all. Making a logic gate with transistors was quite amusing, to see how binary operations work at the very bottom of things. Experimenting is essential, because if you just copy schematics, you don’t really understand how things work and it’s hard to debug.
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