On Mon, 01 May 2006 13:58:50 GMT, (GregS) wrote:

In article , wrote:
Don Pearce wrote:

On Mon, 01 May 2006 13:24:48 GMT, "Michael A. Terrell"
wrote:

Don Pearce wrote:

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.


Its a lot easier to reduce the noise figure at a narrow bandwidth at
microwave frequencies.

Narrow bandwidth? I don't call a bandwidth of nearly 2GHz narrow. And
asitappens, I can achieve these sorts of figure at audio as well.

d

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

2 GHz at 12 GHz is 16.67% which is narrow. Don't tell me that there
is no filtering at all. A circulator or isolator has a usable bandwidth
which keeps out of band noise out of the amp. One of my KU band
receivers is aboard the ISS.

Audio is true broadband, from DC to whatever the upper limit is set
at by the design and limitations of the components if it is DC coupled,
and from less than 100 Hz if its AC coupled.

Not only that, but at low to DC freqs., the noise increases dramatically
of most devices. When looking at op-amps I have to often look at DC drifts,
which is the largest noise.

greg

Tell me about it. I've had to design baffling into a system before now
to control air currents that were causing cyclic temperature drifts.
Generally in an audio amp, though, there is sufficient DC feedback to
render this a non-problem.

d

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