On Mon, 01 May 2006 08:38:56 +0100, Pooh Bear
wrote:



Don Pearce wrote:

On Fri, 28 Apr 2006 15:36:00 +0100, "Dave Plowman (News)"
wrote:

In article ,
Don Pearce wrote:
But being a total of approx 13k will have little effect across 150 ohms.

True - I was just trying to correct your 1.2k, which while hardly a
typo was certainly a slip of the decimal point.

No - that's the input impedance of a Neve desk - one of the classic
designs. Others too. More modern ones may be higher.

One more thing - the Neve mic pre has a pretty poor noise performance.
At -128dBu equivalent at the input, that is about 6dB above pure
thermal noise. That is 4 or 5 dB more noise than they should be
achieving.

Please do your sums properly Don before making gaffes like that !

Graham

Thank you! I did make a gaffe. The actual figure for the Neve noise
figure is about 3dB. That is still unforgivably poor for high end kit
- it is in fact no better than my little Behringer. Ten years ago I
was designing satellite receivers working up at 12GHz. The noise
figure I was working to was 0.3dB.

The last audio preamp I made had a noise figure of about 0.5dB,
because I was willing to use multiple parallel discrete transistors
for the input circuitry. Making it any better than this would have
been possible, but unwarranted because unlike the satellite receiver,
it wasn't pointing at a cold sky, but a warm microphone.

d

--
Pearce Consulting
http://www.pearce.uk.com