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Small vs. large diaphragm condenser mikes for recording grand piano at home
On 05 Sep 2003 19:38:29 GMT, (P Stamler) wrote:
For a pre-preamp to boost up ribbon microphones, assume a minimum microphone
source impedance of 150 ohms. This means, to add less than 1dB of noise, that
your pre-pre must have an equivalent input noise resistance of about 37.5 ohms,
or 0.11uV, or -136.8dBu. Ignoring weighting, that is.
Hi Paul,
A 1dB noise figure is just beyond what I know how to get to. With
the devices I know of, selection, downhill and a tailwind, we get
to 50 ohms equivalent. There are several 60mA/V FETs made, but they
all seem to want higher I-sub-D than we have available.
If somebody (hint, hint) knows of hotter devices, jump in here.
How about making a r.a.p. project?
That's at room temperature. A problem may arise from the fact that, if this is
running off phantom and really drawing 6mA per side, it will warm up above room
temperature, which will slightly worsen the noise performance.
We'll need all the current we can get, and then some. Dissipation
per FET will be about .1 watt. Good point that we'll need to sink
this.
Not a trivial exercise, this.
It's an interesting design exercise, but if we get lucky it could
be a practical construction project. If anyone who's unable to solder,
because of limited vision or dexterity or whatever, would like
help, let me know.
Thanks,
Chris Hornbeck
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