> I cannot see any glaringly obvious circuit reason for using a higher-
> spec op amp, and I guess Doepfer themselves are aware that A-100
> stuff probably doesn't appeal to those people who absolutely insist
> on low-noise *everything*, so my best guess would be that it simply
> comes down to economics - I suspect the LM324 is just cheaper than a
> TL074. I might be wrong though, and so I am willing to be corrected
> by Dieter!

The economic aspect is totally negligible (LM324 and TL074 are in the same
price range below Euro .20). The fine adjustments of the vactrol modules
(A-101-1/2/3) were made at that time by Roland Mayer and I found a note in
his records that he had problem with HF oscillations if the TL074 was used.

Best wishes
Dieter Doepfer