TR-909 / Nava alternative envelope for Crash & Ride?

[dot matrix madness]

I wonder If anybody has got an idea how the alternative Attack/Decay envelope for the Crash and Ride cymbals
of the TR-909 NAVA clone has been realized as given in the Extra9 expansion from Wellental?
What is obvious from the installation guide is that the alternative (retriggerable) envelope is based
on a 555 timer with two potis (attack and decay), and is placed in between the resistor array after the 4520 IC
and the inverting input of the Opamp.

[dot matrix madness]

Being in the process of simulating an 555-based AD generator for this purpose:
Can somebody with a TR-909 or a NAVA and a oscilloscope do me a favor and capture the corresponding
envelopes of the Crash/Ride with different tune settings, so that I get an idea about the voltage levels
going on?
In the TR-909 the points to measure are the outputs of the resistor arrays RA11 (top pin) (Crash) and RA13 (Ride)
located in the upper left corner of the voicing board (viewed from foil side).
In the NAVA it's the joined pins of resistors RA11 A to E and RA13 A to E, also upper left corner.
Thanks in advance!