Ok got my wish and so here's what I see.
The 7802 is quite a bit different from a "stock" Pro VLA. The tube circuit is rather different since the 7802 utilizes a solitary dual triode 12xxx7 tube instead of a pair as featured in the Pro VLA.
The 7802 uses the same style of opto compression as the ART Pro VLA. The implementation is different but the foundation of the circuit is the same.
What I can garner from the views of the PCB is that we have some opamps on sockets which could potentially be upgraded to audiophile components.
I'd also like to investigate how much voltage is going to the plate of the tubes in the 7802 along with how the PSU is set up to see if there's any room for more juice, along with the way the plate of the tube is being loaded. The caps can be upgraded with high end equivalents or improvements so that a low self noise is encouraged. Gotta get a peek at those diodes to see what they are spitting out, it will help us to figure out the game plan.
I see a bunch of film caps of smaller value along with some of the big red film caps that are worthy of investigation, if they can/should be upgraded I'm sure a good quality audiophile film cap would do rather well in those positions.
There's some tantalum caps that have my curiosity piqued...the electrolytic caps (I can't see the value from the pictures) but I'm sure upgrading them to Panasonics or Nichicons can't hurt but I'm always down for rolling values as well at coupling stages to see if we can expand bandwidth.
Last but not least we touch upon the output transformers.
I know from first hand experience that you can make the Chinese transformers in the GAP73 and a few other circuits sound good if you really pimp out the amplifier section of the device however, I'm going to go out on a limb here and suggest that a pair of Cinemag CMOB or CMOQ style transformers would fair thee well. I'd want to see if 1:1 Carnhills or EAs would fit but the stock ratio would be of interest as well. Jensens would definitely be a no brainer.
For the budget (but when performance is still imperative) minded a set of OEPs would be sweet as well.
The Drive circuit is of interest particularly because the Pro VLA has a resistor off the tube that is set for optimal THD so that the unit does not distort unintentionally. Seeing as how the Drive on the 7802 is acting like an input control which can drive the tube of the 7802 into harmonic distortion I'm curious to see what it actually does.
As a recording and mixing engineer's aside I'm rather tickled that the 7802 is considered "better" than an ART Pro VLA. The 7802 offers 2 distinct ratios, no separate control over attack and release and no threshold control (but perhaps the compression control on the 7802 is a reverse threshold??). There's metering for gain reduction and no input or output levels.
Compared to the ART Pro VLA's variable threshold, variable attack and release, ratio that goes from 2:1 to decimate, output control and dedicated dual triode tubes on each channel.
Maybe its the transformers that make the 7802 sexier?
The hi-pass filter is a nice look, the 7802 offers this to help the end user avoid pumping on bass heavy compression. I've recommended other ways around this issue for different opto compressors.
BTW I did some digging while I wrote this and a fellow in Japan upgraded the 7802s transformers with some custom iron among a few other things and so at least we know it can be done
. Obviously somebody has to humbly submit their unit for examination, the 7802 could have undergone some revisions over time. Overall the prognosis is positive.
Simple math tells you that the 7802 is not a cheap donor device for mods. There are definitely cheaper compressors that benefit just as greatly from mods. Some people love the 7802 in its stock form. However there are quite a few things that can be done to open the unit's sound up, improve the behavior of the compressor, the tube section and the overall sonics of the device.