EHX Attack Decay Analysis

[Zveeen]

Hello,
Im currently trying to analyze the circuit of the Attack Decay by Electro Harmonix. While the most parts seem obvious, there are still some things I cannot quite get my head around. While most of the people appear to be fixated on the BBD Delay when explaining how this Pedal works, I am more interested in the Trigger/Envelope circuit. I know how the Envelope cycle operates, but I am not quite sure how it is triggered.
The Flip Flop (CD4013) seems to need a short trigger impulse, since this not only sets the output Q of the Flip Flop high, but it also discharges the charging Capacitor C16 witch one part of the CMOS Switch (CD4066), to make sure every triggered note has a new Attack period. The "Trigger Circuit" should, as it appears, derive a Trigger Impulse from a compressed fullwave rectified Signal. At first glance I thought it might be an discrete Schmitt Trigger, but I'm not sure.That is one part of this Circuit I still don't understand.
I link the Schematic that I rely on with my notes.




Any help on this is very appreciated, thanks in advance
Cheers

[StephenGiles]

The link to your schematic won't open!

[Zveeen]

[Zveeen]

Hope this one works, I wouldn't know what to do else.

[Mark Hammer]

While I wouldn't want to discourage anyone from attempting brave projects, the current-issue digital Attack Decay is a fantastic pedal with much greater reliability than the all analog original.

[R.G.]

I believe that the trigger circuit is a discrete monostable variant of a Schmitt trigger as you guessed. It's fed through a capacitor from the full wave rectifier and has clamping diodes to hold the trigger side at ground level. This triggers a pulse from the two transistors, with the timing determined by C15.
That's the first time I've seen someone implement a full wave rectifier with an actual bridge in a feedback loop. I suppose that with a thirty volt power supply (+/- 15V) there is enough headroom to live with the two-diode drop of the FWB. It uses the same number of opamps as a more common full wave setup with two diodes. Odd.
And yeah, Mark - an implementation in a baby DSP is likely to have better performance. Another place to stick in an FV1.

[Zveeen]

Thank you for all this input.
I have considered DSP before, as a solution for Signal processing, since I'm currently building an Envelope Filter, and I want to be able to really shape the Transients, and not just use the Signals "actual" Envelope.
If the FV1 could do the Trick, it's definitely worth another look, since it is a very beginner friendly DSP.
I guess a small part of me just wanted it to stay "all Analog", but there is no rational reason for this.
Maybe its because CMOS is so fun.

But I still think I'm able to learn a lot from schematics like these, so thanks for clearing that up for me.

I am amazed by how ready to help everyone is, in this  forum, and I am truly thankful for that.
Thank you,
Cheers
   

[StephenGiles]

This works, many thanks.

And the delay line, I seem to remember, is there to help reduce a click noise from the trigger in the output.