Re: gEDA-user: TwoStageAmp example

[al davis <ad136@xxxxxxxxxxxxxxxx>]

On Tuesday 03 April 2007 17:37, Dan McMahill wrote:
> I have to agree 100% with Al here.  The ability to easily run
> the ac analysis at whatever operating point you have, be it
> from an explicit operating point analysis or where a
> transient stopped, is extremely important.  Al's class-B amp
> is a good example because of course the output devices
> undergo very large signal changes and you should be concerned
> with small signal stability over the entire output range.
> Other circuits may not have a d.c. operating point that means
> anything.

The real fun one with the class-B amp is that the usual Spice 
operating point is exactly in the middle of the crossover 
region.  If there really is no quiescent current, the AC 
analysis gives you no output at all.  If you bias it up a bit, 
now class-AB, the current is still low, making the 
transconductance low, making the output impedance high, still 
useless.

Try a two-tone test and you can see a reason why some early 
transistor amplifiers sounded so bad.


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