The question was intriguing, so I had a good look.... It's embarassing to read so much about one's own work! David was very kind in his write-up; and he managed to catch most of the little features that make the old JM compressor sound the way it does.
But to get to the point.... The question was about what additional bits or features I would have added if there were no budget restrictions, and the answer is absolutely none.... Apart from the cheaper offerings in the old JM range, I never did work with budget as a major factor; but I'm a very firm believer in not putting in expensive bits just for the sake of it!
The original JM compressor was the result of a need for a stereo mastering compressor for a little video project I was doing in 1992; it was a travelogue of the West of England, and needed some gentle compression that I did not find in the gear I had at the time, so I built my own.
David picked up on the main points; the strange curve of the opto cell, and the dual time constants, but he missed a couple too!
The old SC2 had a slightly 'floppy' power supply that sagged with the demand of the LED drive servo! I did know about this, but it sounded wonderful!
Another big factor that David did approach, but made rather 'heavy weather' of, the sidechain filtering; it doesn't have much to do with hearing curves, it's more to do with voltage peaks and energy; to get compression that sounds right you need something like 'constant amplitude' in the sidechain feed. David chose a complicated filter arrangement that need not be anything like that, simple first order filtering is fine.
I have played with 'Vactrol' devices but prefer to stick to descrete opto cells and LEDs.
The WHAT Compressor also has this uncompressed side path for transients... No, I tried a few tricks like that but prefer careful control of the attack and release characteristic, once it's right there's no apparent loss of transients... unlike VCA types! :?
As a project, the WHAT compressor looks really good; it contains a host of good engineering ideas and will certainly work well. It differs from commercial design in that commercial equipment has to be as bomb-proof as possible; must be balanced in and out, and must be quick to produce, easy to test and very reliable.... not that it isn't! I think it's admirable.
Trying to comment and answer the question is difficult because we have all moved on from the 60s, and even from the late 90s... my current compressors are still optical, but the cell is in a 'bridge' circuit that allows me to 'lever' the compression ratio over an extreme range.
I like to think they are just as easy to use, and a lot prettier(!)
:grin:
