Not too sure about synths.
But I did run in to circuits that where designed around the slow slew rate of older 4558 ics.
one in particular was a Tube Works amp that had a 12AX7 blow out that toasted the 4558.
I installed a modern version of the ic & the customer wanted to know what was wrong with the amp.
The distortion was NOT the same.
So, I grabbed the ic from the reverb circuit & swapped them around & wallah. Customer happy!
Another instance was the original Tube Screamer pedal.
Same thing.
Modern ic is too fast. slew rate wise.
By this time I had accumilated a 'stash' of older 4558s.
Installed one of them. Problem solved.
But I did run in to circuits that where designed around the slow slew rate of older 4558 ics.
one in particular was a Tube Works amp that had a 12AX7 blow out that toasted the 4558.
I installed a modern version of the ic & the customer wanted to know what was wrong with the amp.
The distortion was NOT the same.
So, I grabbed the ic from the reverb circuit & swapped them around & wallah. Customer happy!
Another instance was the original Tube Screamer pedal.
Same thing.
Modern ic is too fast. slew rate wise.
By this time I had accumilated a 'stash' of older 4558s.
Installed one of them. Problem solved.