On Thursday, February 14, 2013 12:23:37 AM UTC-6, Trevor wrote:
wrote in message
...
Worst case signal for slew rate tests is to jangle keys in front of a
high-bandwidth microphone. Of course once it hits an a/d converter it gets
band-limited to 20k so after that there is no issue.
Not with a 96 or 192k sample rate it doesn't, but you'd have to look hard to
find an amp that can't handle the frequency response of a microphone without
slew problems these days anyway.
Which is a result of people paying attention to the issue back in the 70s and 80s.
Part of the problem back in the way-back was that this was the beginning of the transformerless era; people were champing at the bit to eliminate the transformers at the outputs of mics and the inputs of preamps which colored the low frequencies (and took up space and added weight and cost more money). What they didn't necessarily realize was that the ultrasonic bandlimiting the transformers added helped prevent nasty slewing issues and IM distortion.
By the way, my apologies for an error: the tests that showed high-frequency distortion in opamps that were not into actual slewing came from Walt Jung, not Sam Groner. They're in "Audio IC Op Amp Applications"; unfortunately, my copy is buried at the moment, so I can't get the page numbers.
Oh, and anyone who wants the Groner opamp test results can download them (the file is about 35 megs) from:
http://tinyurl.com/opamptests
Peace,
Paul