This one’s an experiment and there’s a real chance this initial version won’t work correctly, so keep that in mind if you’re trying this right away.
I took the service manual schematic that’s floating around and removed the portions related to the effect switching and the buffered bypass (or so I believe at least).
And from this I put together a fairly large layout.
There are a few uncertainties here. I grounded the now-unused parts of the LM339 (from the switching stuff I left out). The original uses an XR4212, but unless there’s something special about this particular IC I’m sure most quad opamps with a compatible pinout would work (e.g. TL074). The circuit contains two trim pots that presumably will need to be adjusted for proper circuit operation. The schematic also hinted at two resistors possibly having to be adjusted based on some setup routine (R53 and R60; see the schematic notes). I’m also assuming you’ll have a hard time finding a dual C100k pot, but a linear taper one is probably a second best.
I’m going to try building this (I do like those compressors), but I’m missing a few components and will have to source them, probably from over-seas. Let me know what your experiences are if you are brave enough to give this an attempt. (A quick google search seems to suggest the AA/119 is in fact the 1N60 germanium diode which I have a few of, but I’d like suggestions on a replacement for the BC558Bs).
Update (16.03.2013): Built this and it seems to work 🙂 All controls respond as expected, and there’s lots of compression and equalization happening.
First off, I had a small typo on the initial layout that has now been fixed.
I kept R53 at 1M, but didn’t have a 6M8 so I used a 10M for R60. Both trim pots were initially set at 50% and I didn’t try tweaking them as it seemed to work (I’ll experiment with these when I stuff this thing in an enclosure). I used an LF347 for IC1, though a TL074 would have probably worked just as fine. I found a couple of BC558Bs in my drawer so I haven’t experimented with any replacement for these.
Next step; how to fit this in a 1590BB without using a hammer…