As I’m waiting for some money to magically appear on my bank account to fulfil, finally, my modular wishes I decided to spend some time on a circuit.
I wanted to build something to put the grey matter in my vaccum fueled head at work. But not the usual ADSR and such, something a bit unsual. First, I wanted to reduce component count as much as possible (as always) and use ICs rather than discrete transistors. I totally failled as you’ll see. My CD4013 aren’t in the place yet so transistor it will be (at least for proof of concept). Beside, it’s nice to build circuit from discrete transistors in this period of integrated circuits.
The idea is to create an unsual envelope (which has certainly be done before by the way). I want two independant segments, the usual attack/decay part but an “hold” time in between. Both independent of each other.
But before that, I had to make the first part working, a simple attack/decay.
It’s rather similar to what can be found on the internet. MFOS for instance has one like this. But I built it with transistors. It’s simple : a gate turn T6 on for a short time, D1 reaches ground, the fliplfop changes state. C4 charges through the attack pot. C4’s voltage is monitored by IC2b comparator. When it goes higher than 10V, the output goes high, triggers T7, its collector goes at ground, the flip-flop is reset, C4 discharges through Decay pot.
You may notice that a lot of parts are used and a CD4013 will reduce the flip flop to a IC. But it’s fun and considering the price of cheapo 2N3904 (you can buy hundred for less than 2 dollars in ebay with shipping from the Mother Hearth Of Electronic (China)) I think every electronic geeky geek has a bunch of those.
The other interesting thing you can do is to add a repeat fonction. An LFO if you will. The speed and waveform will depend of the attack and decay pot. The overall speed is controlled by C4 (lower value = higher speed). With attack=decay=2K2 and C4 =72nF, you obtain 1.8Khz, not bad !
A second comparator is used but in the opposite direction. When the voltage goes lower than the threshold the output goes high and creates another pulse on T6’s base.
This is an easy circuit to build and you can even multiply it on a stripboard to have a module containing 4 of this. It isn’t the most advanced one but could prove itself handy when you need a simple envelope generator.
I’m a bit tired and need rest, I leave it as it on the internet’s archives (and for people who wants to have fun with transistors). I’ll expose the original idea circuit in another post to not make this one bigger. A little tease, it uses a 555 timer…