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Original Message

The design is immune to the opamp.

Posted by Ralph on July 10, 2017 at 10:16:13:
Years ago I worked on an old Berning TF-10 which also has a direct-coupled output also controlled by a DC servo. In that preamp I noticed that the choice of opamp made a difference in how the preamp sounded, as the servo was also acting like feedback.

So when the MP-1 was designed, it was a top priority to make sure that the opamp couldn't affect the sound. It is a tube preamp after all :) Part of this was to make sure that the servo really was working on DC and was not also processing audio signals (which was not true of the old Berning).

This was done by employing a more sophisticated filter design and the result is the preamp really doesn't care what sort of op amp is used. The same circuit is in the MP-3.