I am not that well versed in subtleties of specmanship not I have a golden ear. My daughter is a budding musician so this came up. I am tempted to build her decent mic preamp but not for a PA system. Than again I am not inclined to use bits of silver wire and solder during full moon either.
-- Boris
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The 990 is really old, and in those days +99dB into 600r was a requirement. That drive level is not really required now
Full moons and whisky are important social events, but you can go either of two ways get a good mic transformer, sowter/ jensen and a good opamp, even a NE5532, is still pretty good, but the latest "audio opamp" from National looks good or Get the latest Thatcorp offering.
Do not expect a cheap wallwart transformer to be any good for quality audio
It is reallly a matter of construction. Good hygine in the layout and supply decoupling and grounding is essenstial, as is a reasonable set of test equipment.
Why not build one of each? Personally, I think a transformer input is generally more bulllit proof, despite the extra cost
Martin
As long as you can use supply voltages around +-15 volts, I think you can pretty much substitute an LT1128 or LT1124 and get results that sound pretty similar. They have nowhere near the output current capability of the 990, but I don't think that matters for a mic preamp. Oh, you also get two opamps in each package.
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