http://www.sengpielaudio.com/calculator-volt.htm
NF calculation is relevant to optimizing a circuit's operation for a given source impedance and BW. It's adequate for optimizing a discrete design, not so much for opamps which, in most cases do not let the user vary its operating point.JohnRoberts said:While the author dismisses using NF to characterize noise performance, he is talking from the perspective of an op amp salesman.
I like using NF to evaluate a circuit design because it clearly states how far from ideal (noiseless) it is.
JR
I believe we would agree that both methods are aimed at different evaluations. I guess that's why we learnt both and have found out when one is more useful than the other.JohnRoberts said:I guess it depends on what are the variables you can adjust.
Op amps can and do have optimal source impedances, and in VE applications you can tweak those impedances (over a range) with resistor value choices.
In mic preamps, even though the source impedance of the microphone is a given, using a step up transformer can adjust that source impedance to better match a given op amp.
While I think talking about (optimizing) noise too much in the context of VE summing is missing the rest of the story (phase shift and distortion). The noise floor of most consoles is dominated by other circuitry.
I preferred NF when talking about mic preamps because consumers were generally confused by dBu numbers that were not always comparable apples to apples, due to different measurement bandwidths or other factors (shorted input, etc). NF reveals how close the preamp is to ideal so hyperbolic claims in advertising were easier to negate.
JR
JohnRoberts said:While the author dismisses using NF to characterize noise performance, he is talking from the perspective of an op amp salesman.
I like using NF to evaluate a circuit design because it clearly states how far from ideal (noiseless) it is.
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