[Michael Maurice]

A manufacturer will design a piece of equipment based on research in a laboratory, he will then test his design and when he thinks he's got it right will start producing the item in bulk.

But after you've made a few thousand, certain problems that didn't show up in pre-production now do, so the manufacturer tries to find a solution and when he's found that solution incorporates it into the production line.

That applies to every product be it electronic or mechanical. Just look at the number of cars that have to be recalled for safety checks.

As Ted has said, Studer used the very latest technology available to them, dont forget the A700 came out in 1973 when IC's and especially large scale IC's were in their infancy.

Having found a noise problem, Studer went on to modify it in the next generation of recorders but would it have made sense to redesign the repro amp for the few that might have noticed the increased noise?

The other point to make is that theA700 uses +/-12V rails where as the A77 and B77 use a single 21V rail.

If as Ted suggests the problem with magnetisation occurs because of the different decays of the supply rail, you could always try doubling or tripling the 12V supply reservoir capacitor.