I'm posting these details to make them generally available. The Crown VFX-2 filter/crossover is a well regarded and respected device, with working models still commanding prices around $200. There has been a lot of controversy on a number of forums, as the circuit has not been linked. There has been a lot of debate on how to approach the NLA OP-AMP ICs.
About 10 or so days ago I suddenly got a pretty loud hum and hiss from my left rear back speaker. The Crown VFX-2 was soon found to be the problem.
Now since I'm a hoarder, even though I purchased the unit in 1977 for long gone Margaritte's Music in Moorehead Minnesota, I still have the original owners manual. Back then a manual contained a full circuit and parts list. That is a practice that should never have been abandoned.
This is the unit in question. It is the fourth unit from the top. The black unit is the right most rack, fourth from the top,
Now my unit contained 10 NLA RT7412 dual op-amp ICs, one of which had failed.
After research I ordered a packet of 20, Texas Instrument PRC4558IP ICs from Mouser Electronics. Mouser
Part Number: - 595-RC4558IP.
The price is $0.301 a piece. With shipping it cost me all of six dollars!
I checked the caps and all seemed fine, so not wanting to fix what was not broken, I left them alone. I changed all ten of the dual op-amp chips with the new ones. I did clean the switches and pots with electronics cleaner while I was inside.
The unit fired up right away and is now better than new. The old ICs, had a very slight hiss you could hear putting you ear up against a speaker. The unit is now totally quiet and back in service.
I have posted this in the hope it will show in an Internet search for anyone looking for advice on these fine units.
I can confidently recommend the TI PRC45581IP dual op-amp ICs as a replacement for the originals.