>> ... You have also ignored what I said about supply
>> headroom.

"Headroom", in this context, is the amount of voltage swing available 
at the amplifier's output. While some amplifiers can swing (= vary) 
their outputs all the way from the positive to the negative supply, 
many don't go all the way and require a "buffer voltage". A typical 
amplifier may require say 2.5v between positive supply and the maximum 
output voltage. It may also require 2.5v between the minimum output 
voltage and negative supply. This would mean that if you used a 7 volt 
supply with this amplifier then the output could only swing from 2.5v 
(0+2,5) to 4.5v (7-2.5) allowing only a 2v output swing. The same 
amplifier used on a 5 volt supply would have NO available output 
swing.


            Russell McMahon

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