Looking at the OP37 (for example) with a noise figure of 3nV (root Hz). If I were using this as an audio pre-amp with a gain of 5 how does this translate into the kind of S/N figures usually specced for amps eg -NN dB ?
Dirk
Noise in audio + opamps
Mar 05, 2007
3 Replies
You have to do the sums
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page 150 gives you the lowdown. depends on source Z, bandwidth, temperature etc. +-1audiophool
martin
Thanks Quite interesting.
Dirk
You need to think about the impedance of the source before choosing the op-amp, in case you have not already.
You would probably benefit from reading Douglas Self's books, in case you don't already have them. On page 83 of "Self on Audio" he mentions that in one particular circuit, the 5532 was measured to be quieter than an OP-27, even though the datasheets would lead one to expect the opposite. I think it is something to do with the bias current cancellation scheme in the OP-27/OP-37 which introduces common-mode noise current, though that only matters when the impedance presented to the two input pins is not equal.
Here is some stuff about op-amps and audio
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Chris
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