I attended one of Roy Gregory's demos of (among other things) equalization issues and their remedy with the Zanden. The differences are not well explain IMHO by merely the vagaries of mastering. I also researched a bit the RIAA standard and when it was adopted, and though 1954-55 is the date the pre-emphasis curve was 'adopted', there are comments that it was not universally used by all until years later, perhaps in some cases more than a decade later.
It is also not implausible that some existing mastering suites were slow to use the RIAA curve, for reasons of cost and convenience. I'm speculating here, but given how well the alternate playback curves worked in improving timbre at the demo, I think these LPs were mastered with the older curves they were used to using. This contention is bolstered a bit by the observation that this isn't found on just a few LPs of the label, but seems pervasive with a label, e.g. DGG recordings of the late 50s and early 60s often seem 'muffled', with apparent roll-offs at the top and too much lower midrange which deadens string tone among other things -- when using RIAA de-emphasis that is. (At some point this changed.) Perhaps it was also assumed that few people would honestly hear the difference, or know why it was there, or there was a concern that loyal customers of the label were already using 'their' playback curve and they didn't want to disturb their customer base.
In any case, I think that for serious collectors who have many non-US recordings of the 50s and 60s, a phono stage with more de-emphasis choices is desirable. Tony Cordesman reached the same conclusion when reviewing the re-do of the Citation I preamp. This unit might be a good choice, though it may lack ultimate clarity and transparency which to me reduces its appeal. YMMV.
Jeff
It is also not implausible that some existing mastering suites were slow to use the RIAA curve, for reasons of cost and convenience. I'm speculating here, but given how well the alternate playback curves worked in improving timbre at the demo, I think these LPs were mastered with the older curves they were used to using. This contention is bolstered a bit by the observation that this isn't found on just a few LPs of the label, but seems pervasive with a label, e.g. DGG recordings of the late 50s and early 60s often seem 'muffled', with apparent roll-offs at the top and too much lower midrange which deadens string tone among other things -- when using RIAA de-emphasis that is. (At some point this changed.) Perhaps it was also assumed that few people would honestly hear the difference, or know why it was there, or there was a concern that loyal customers of the label were already using 'their' playback curve and they didn't want to disturb their customer base.
In any case, I think that for serious collectors who have many non-US recordings of the 50s and 60s, a phono stage with more de-emphasis choices is desirable. Tony Cordesman reached the same conclusion when reviewing the re-do of the Citation I preamp. This unit might be a good choice, though it may lack ultimate clarity and transparency which to me reduces its appeal. YMMV.
Jeff