Seventh Circle also makes a Jensen Twin Servo preamp. You can put the Hardy op amps in it. Not a 500 series, though. I've never used it, or a Hardy for that matter, so I have no idea how any of them compare. But, I am really interested in the answer to this question.
Quote:
Originally Posted by
Jim Williams
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Hardy uses one opamp. The Jensen design cascades two.
The M1 is his single op amp preamp. The Twin Servo 990 uses two.
http://www.johnhardyco.com/pdf/TSMP2015-03-01.pdf