Where do all those volts go?

[Stocker]

http://www.kitsrus.com/projects/k48.pdf

This is a simple amp, for an example. It uses a darlington-arranged output, and bootstrapping, and a little degeneration. With 18Vcc, it swings 4Vout Max. Why? I know I am missing something but what?

they say: 18V+, 2W out into 8ohms, 4V.

=0.5A out yes? so across the 1R2 resistors you get

1R2 x 0.5 = 0.6V (x2 resistors =1.2V)

and the same 0.6V approx. per output device

=2.4V

okay? so you have 4V across the load, 2.4V across the output stage, and 4 + 2.4 != 18

so where did the other 11.5V go?

This is an exapmle- I see this all the time in amplifiers simple enough for me to figure out.

And question two: stability issues aside, will the max Vout increase if the 1R2 resistor value is lowered?

[bigparsnip]

I think what you may have here is a 4V rms out put, so you have to look at what is happening over the device.

Basicaly, for a 4V rms sine wave you will have +/- (4 x 1.41)V accross the load, which works out at about an 11.3V total voltage swing. Then if you take the value of the voltage drop you have above for one half of the circuit and multiply this by two (it's a push pull type, so you will lose this on both the upper and lower rai sections) of 2.4V (which is probably a little low) this will give you a total af almost 17V which is much closer to the applied voltage to the system.

[Stocker]

To paraphrase:

6.4 x 1.414 =9ish x2 =Vcc

makes sense.