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Thanks for that! Yes, that's the transistor I was referring to - I mistakenly wrote 2sD and I knew there was a 7 in it somewhere but... ?
But, as best as I can tell with my test gear, it measured .7nV/rtHz which isn't too shabby really.
I don't know what he plans to do with this little circuit but, if I can, I'll try and post a schem.
Regarding Rbe: Linsley-hood demonstrated that some mighty fine noise specs can be had by using just a single pair of medium power input devices rather than the small signal TO-92 type. An Rbe of 4 is not uncommon for some of these medium beefy globs of silicon.
At the end of the day, the active electronics inside the mic will probably dominate the path performance. I know this is an area of Ricardo's interest and expertise, not mine.
It's about sub nV/rtHz noise performance.
I think THAT Corp offers two parts identical except these resistors.
> was a rch (old machine shop term)An engineer tole me it was an old engineering term, slightly larger than the mythical BCH.
In a prior post, I boasted a .7nV rt Hz spec but, this time I come up with somewhere round about 1.2nV rt Hz. Not exactly terrible, but it isn't as good as Samuel's efforts and the rest of the best.
It's worth noting that typical dynamic microphones have output impedances of several hundred Ohms. Getting low current noise is at least as important as low voltage noise.
Quote from: Jean Clochet on April 14, 2012, 11:17:58 PMIn a prior post, I boasted a .7nV rt Hz spec but......I'm sure all of us have had similar experiences
In a prior post, I boasted a .7nV rt Hz spec but...
An earlier discussion of parallel devices to reduce noise can be found in "Low noise Design" by Motchenbacher & Fitchen c. 1973
While Leach's entire website (RIP) is worth reading.
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