Re: Uli Behringer of The Music Group Q&A
While this is perhaps TMI for this forum, since you mentioned the actual ICs used, the JFET input TL072 and bipolar input NJM4580 are not generally considered similar enough to be interchangeable.
Among the several notable differences the 4580 is a lot lower input noise but with slower slew rate. The slew rate is still fast enough to deliver a 60kHz+ power bandwidth so not an audio performance limitation.
The 4580 should deliver lower noise in circuit when properly applied. Since many manufacturers use the same palette of component parts, execution or how these parts are applied matters. I do not know what you pay for parts but my guess is that the NJM4580 should be lower cost than the TL072, so a win-win. If true that begs the question why was the TL072 used in the first place but better is always better (Kaizen).
JR
PS: I believe you could have a future writing bullet points for FAB copy. 
