Very interesting!
But it should get a different power supply that works with a standard 9VDC adapter.
Maybe use one of these cheap chinese dc-dc-converters that can deliver +/1 12V, and put two 7.5V voltage regulators and filter caps on the board?
http://www.ebay.de/itm/282562725196?ul_noapp=trueIf you use two TL074 and omit the space for a battery, it could still fit into a 1590B
regards, Immo