There is a distinction that needs to be made between the Dynamics card (which takes care of compression and expansion) and the VCA card which deals with the computer VCAs.
Having said that the early version DYNAMICS card (pre 1983, but there is no definite date for when they made the transition) used a 1537A type VCA,
then the followed as Sintech says with DBX or That corp chips.
also quoting from a well respected tech:
"
Dynamics card:
The Dynamics card is based around a VCA. Initially it was based around the B&B 1537A VCA, which came in a 14-pin DIP package. Supply variances and some other difficulties forced the design to be ported over some time around 1982, to use the dbx 2151 type VCA, which came in an 8-pin SIL package. -While there may not have been a great change in sonics at the time, the later evolutions of the SIL design by the THAT corporation have improved the performance DRAMATICALLY, and I have no compunction whatsoever in repairing broken cards with the newer THAT designs, should an older dbx require replacement.
Other than the redesign to accommodate the VCA change, there has been little significant change to the dynamics card, with only incremental tweaks to later revisions.
VCA card:
As distinct from the dynamics VCA, the FADER VCA card also went through a couple of revisions. The format was ALWAYS the 'large-can' dbx style, and earlier ones had the gold cans. Sometime around 1986, the gold cans were dropped for a replacement -also made by dbx- which comprised a daughter card containing EIGHT of the smaller SIL-style VCAs in parallel, and a low-noise op-amp to drive the control gates at a suitably low source impedance.
Also on the VCA board are a couple of other functions such as small fader buffer, and the FET switching for fader swap between VCA and small fader. There have been a good number of incremental revisions made to this board, but in terms of signal path the VCA swap has been the only one of major significance."
I how this helps.
Mattia.
