[sdiy] why +/- 15V

[René Schmitz]

Hi Jürgen, Nils et al,

Next question: Why 10V signals? :-) This is more of a hen / egg thing 
IMO. A 0.1V/oct and 100mV signal level would do also.

Cheers,
  René

jhaible at debitel.net wrote:
> Higher voltage, better SNR, or headroom, depending on your
> nominal signal level. For the following, let's just assume
> maximum level without clipping, and look at SNR, to
> simplify things.
> 
> At first glance, 30V (+/-15) are just 3 times as high as 10V.
> So with the same noise level, you'd get 20log(3) = 10dB
> better SNR from 30V supplies ??
> 
> Actually, many standard opamps don't like to go near their
> supply rails. Let's say 3V distance to vdd and vss.
> So your maximum signal amplitude is 24Vss (30V) vs. 4Vss
> (10V supply). That's 20log(6) = 16dB better SNR from the 30V
> supply!
> 
> Modern rail-to-rail opamps, and generally better low-noise
> parts will improove the situation, of course. So some of
> this +/-15V idea *is* historic.
> 
> I like to be "historic" in most of my own designs. And I
> even see the benefits you get from this even older technology
> that uses +250V, allthough I rarely use it myself.
> 
> JH.
> 
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