The NJM4580 is a very old opamp from JRC. It can be upgraded with a Burson dual Audio Opamp.
However, anyone considering this upgrade should confirm that the supply voltage of the machine is better than +/-12V.
NJM4580 data sheet: http://www.scribd.com/doc/23880293/NJM4580-Opamp-Data-Sheet
what would happen if the supply is lowen than 12v ?
You will not get the best result. The HD Opamp will work as low as +/- 10V but not lower.