EDIT:
I am reasonably sure I’ve got this right, so here is the full stripboard layout to get two LMNC simple AD/AR generators in one module. The long green jumper wire is an optional “normal” output, that should go between the tip switch connections if you have a switching jack. I am building/testing trhe second half now, I’ll correct if there are any mistakes.
Please note that there are some quirks with the circuit (whether you go single or double) which are detailed in the comments below. Also, the potentiometers are as seen from the back, which is the opposite of Sam’s diagram.
Enjoy!
Hi all,
I am putting together a dual AD/AR Generator (the 2.0 version with a switch and push-button), and I plan to release the stripboard layout as well as the STL file for my 3d printed panel. I’d like to make sure I have everything working first though, and so far I just have one small problem - has anyone experienced the following?
Everything works great except the Attack knob when the module is set to Trigger (AD) mode. Only about 5% of the knob’s travel from counter-clockwise is useable. If I put in too much attack time, the module won’t trigger at all. I have only tested with the push button, not an external trigger. I have double checked all the resistor and capacitor values, and even swapped out the 10nF cap with two different replacements (same value) to see if that would do the trick - no luck. My suspicion is the capacitor, since there are very few components that would affect the trigger but not the gate. Any insight is much appreciated!
In the meantime, here is my first draft of a dual envelope stripboard. I am reasonable certain it is correct but I will post a version with all the outboard wiring displayed after I am fully certain nothing is wrong with the layout.
btw, if that can give you an idea, on mine I added a switch to select the cap 1uf or another of 2.2uf (short or long envelope), and attenuator pot on the output it is always practical I find.
Indeed, I intended to put a attenuator on the output and and forgot to leave space for the extra pot sigh. Practical indeed, though.
As for your other comment, I believe the full attack decay cycle should occur on a trigger if memory serves, perhaps I need to go check my other envelope gens to confirm.
a trigger signal is just an impulse (unlike a gate signal which can be much longer), so on just one impulse it is difficult to have a long attack and similar for the release
Typically it should (I can’t speak to this particular circuit). A trigger is very fast, it doesn’t make sense for the release to start when the trigger ends.
I believe even if the envelope is set to trigger mode, you should still get the full envelope cycle if the incoming trigger/gate is long enough. A very short pulse will go straight from Attack to release regardless of the mode, where as a long gate should attack, hold for the duration, and then release when in gate mode. When in trigger mode, I’d expect a long gate input to attack and immediately decay when the peak of the envelope is reached. It should go through the the full attack time so long as the incoming signal is high for at least as long as the duration of the attack.
Indeed, the problem is that even if I hold the input high indefinitely, the envelope will never trigger at all (in trigger mode) if the attack time is longer than a tiny fraction of a second
It may be a matter of terminology, what’s being called here “trigger mode” and “gate mode” are what I’d call “AR” and “AD”, with either one requiring a long gate. But you’re giving it a long(ish) gate if you’re using the push button. So I would expect you to get the full attack. But again, I may be misunderstanding the intention of the circuit.
Not just you, on the diagram the switch is labeled “gate” and “trigger” but I think that refers not to the expected input but to whether it sustains after the attack (if the gate is long enough) or not. (But up top it’s called an AR/AD switch.)
I’m not sure I get the terminology (specifically, how is attack-decay different from attack-release if there’s no sustain level?) but from what I can tell from the schematics, the trigger input is basically an edge-triggered gate pulse generator. The trigger signal is connected via a 10n capacitor, and the diodes and resistors that follow turn a positive edge into the equivalent of a 1-2 ms gate pulse (if my numbers are correct, that is – may measure on the actual circuit if I find the time).
I would expect this to result in a very short attack, followed by a release that depends on both the attack and the release settings (if you set the attack too high and trigger it with a short pulse, the output level will never hit max, so the attack setting kind of turns into an envelope level control.)
EDIT: The pulse timing depends on the trigger voltage; the first opamp stage is a comparator with a threshold voltage of 12V×10k/(10k+47k) = 2.1 V. The closer you get to this voltage, the more likely it is that the circuit doesn’t work well.
Wow, I only hope that one day I can glean that much from a glance at a stripboard layout. Thanks for the insight, it sounds like the circuit is working as designed. I might give Sam a little feedback to make the quirks more clear on the project page to save us the needless troubleshooting.
This also makes me consider the idea of using a dpdt switch to somehow lock the attack at 0 when in AD mode so that the EG doesn’t suddenly stop working when you switch modes with the attack up.
Anyway, it seems like my layout is functional, I will release the rest of the materials as soon as I get the time. Thanks all!
-Wes
Just wrote this over at Patreon in reply to your issue with trigger voltages, but copying it here as well for reference:
"The trigger pulse depends on the input voltage; the next stage compares the filtered signal with a 2.1 V threshold, so if that 10 nF capacitor doesn’t charge up enough, the signal will spend very little time above that threshold, which affects the decay/release cycle as well.
"To make this really robust you probably need an input buffer to make sure you have a constant trigger voltage no matter what you connect it to, but you could try messing around with the threshold voltage divider (the 10k and 47k to the left of the opamps). E.g. try soldering in another 10k in parallel with the existing one; that would lower the threshold to a bit over 1 V.
“Another option is to make the threshold adjustable, by replacing the 10k/47k pair with e.g. a 100k trimmer between 0 and +12 V, with the wiper connected to the negative opamp input (you can use the same trimmer for both opamps).”
Thanks for the valuable insight as usual Fredrik. I got side tracked with the dual expression pedal but I am going to give your suggestions a shot as soon as I get it buttoned up!
Hello!
I built the single version of this EG, and I have the same problem. The “trigger” mode doesn’t seem to work when the Attack is turned up even a tiny bit. I installed the 10K in parallel as suggested, at least this helped with the external triggering. But the issue is still there, I can only use the trigger mode with the Attack turned all way down.
Is it something that’s normal?
sigh. Practical indeed, though.