Hi, I am currently building this Kassutronics envelope generator and I would like to add an LED for the input as well. Where should I put it?
My idea was to put it after the Schmitt trigger (between R2 and C1) to have it really only showing when the asr triggers. But then it will probably also light up when the sustain is still up, right? Then maybe simple at the input, before or after R1?
By “it” I mean a copy of the LED driver (which I will probably replace with a simpler version with just one resistor in the LED current path).
You could connect it to pin 1 of the op-amp, so it does not put an extra load on the output of the device connected to the input. And rather than decide whether to put if after the Schmitt trigger or at the input, why not do both?
B.t.w. in the current schematic the output can also produce negative voltages, but then your LED won’t light up. You could use 2, one connected to the + and one to the - power supply (each having their own series resistor (of say 1k Ohm for 10mA current)) and both the output of the op-amp. So one will light up for positive and the other for negative output voltages. The op-amp should be able to supply sufficient current so you can leave out the transistor.
With this you mean two LEDs? or connecting one to both points? I thought: when I put it after the Schmitt trigger I have the direct signal of when the envgen really triggers. What would be the advantage of connecting it to both?
I didn’t understand @Jos’s answer either — in the schematic as shown there’s a connection from +12V to the transistor collector via a resistor, but then he talks about leaving out the transistor in which case, yes, it’d just be from the output to the resistor to the LED to ground. Or two antiparallel LEDs to have it light up for negative signals as well, or a bicolor LED. But I don’t see why this envelope generator would be producing negative outputs.
As for placement of the input LED, I’d say just breadboard it and try out locations to see what you like. Between R1 and R2 won’t work, that’s a virtual ground.
Switching the loop switch S1 disables the Sustain circuit and bypasses D5. Now, the STATE signal is connected directly to both the charging and discharging side, and the circuit becomes a standard relaxation oscillator. This generates a bipolar triangle-like LFO waveform, with adjustable rise and fall rates (by Attack and Release, respectively), with output levels of approximately +/- 8V.
I am not yet sure what this means when I connect it to a VCA and if that’s good or bad, but I am going to find out, I think
Is there a schematic for that one? I would like to have a look where they put the manual trigger button. Maybe I can just make a voltage divider to get 5V and then connect that to the input via a button?
I think it’s not virtual ground, because the output of the opamp goes into the positive input, but as I said before, I am only beginning to get a grasp on this
In any case, I am going to breadboard this! Still need to find out the best way to get ±12V to the breadboard…
Yep, but this would not indicate signals lower than the diode’s forward voltage Uf, so this would introduce a <add 4 notes from the movie Jaws here> dark void between +Uf and -Uf !
I was trying to point out 2 possibilities: 1 to add some signalling for the input and to the Schmitt trigger and 2 to make it suitable for positive and negative voltages. One led + series resistor from the op-amp to -Vcc and one led + series resistor from the same output to +Vcc. If you want to avoid the dark void between -U forward and +U forward you could go for a bit more complexity as I’ve used in Pedal-O-Matic, which looks nice, but may be a bit much:
The opamp would love to provide a virtual ground, since keeping the inputs the same is its main purpose in life, but it’s wired up as a comparator (*) and not an amplifier, so it cannot do that. But not for lack of trying.
If you’re only looking for zero crossings, you can just feed the signal to one opamp’s + input and tie − to ground, and the output will swing to max when the signal crosses zero (if the input can be outside the safe common mode range, add a voltage divider on the way in). Doesn’t give you the same trimmability, though.
Ah, right. I wonder if you could get a decent result with the simplest possible “precision rectifier” layout, i.e. a voltage follower with the LED inside the feedback loop. Odds are the LEDs are a bit too non-linear for that to give the appropriate visual result, but I might have to do some experiments…
