John Curl's Blowtorch preamplifier part II

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OK, I made a brief simulation on push-pull class A dissipation. I used some real circuit to make it quick. This is a primary school of power amplifiers. Power (red) is for 2 different output amplitudes. Blue is a current (idle of some 1.6A) thru one output device for two different output voltage amplitudes.
 

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Chris:

You're making a good point, often overlooked by engineers.

The effect of this issue, is often causing issues in both electrical and mechanical engineering.
One of the main reasons that the "calculations is the only way" attitude seems to cause problems, is that often tolerances are not taken into account in the equation, as it would make the equation quite complex.
Safety factors are relatively easy to feed into an equation, but when you have a tolerance in both ends of the scale, so to speak, it's all of a sudden a quite different ballgame.

I see the result of this quite often in my everyday job.
Either tolerances were not summed up, or over engineering, making the final device malfunction.

So much for simplified equations.

Magura :)
 
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PMA said:
OK, I made a brief simulation on push-pull class A dissipation. I used some real circuit to make it quick. This is a primary school of power amplifiers. Power (red) is for 2 different output amplitudes. Blue is a current (idle of some 1.6A) thru one output device for two different output voltage amplitudes.


Nice to see the freq doubling confirmed ;)
Quiz: what is the relationship between load resistance, bias current and supply voltage to make the dissipation curve linear? Is there such a condition? Hint: if Iout doubles, but Vce halves, dissipation remains constant.
(A simplified equation will do). Any engineers out there?

I'd do it myself but I need to go to a Masterclass Tube Design :D. Really!


jd
 
FWIW, in various appnotes (eg from Apex) I find Stinius' equations... so that's seems to be right.

In the Apex AN01 there are some equations for reactive loads, extending the one for the resistive case.


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@Jan: I think there is no way to get constant power with real world complex loads and EF's/SF's unless one uses cascodes which generate an (approximated) optimum load line for the instanteous current, regardless of voltage (as they aren't corelated).

Other way would be not to use plain EF's/SF's, then...

- Klaus
 
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john curl said:
Equations look good, so far.

The equations are good

KSTR said:
FWIW, in various appnotes (eg from Apex) I find Stinius' equations... so that's seems to be right.

In the Apex AN01 there are some equations for reactive loads, extending the one for the resistive case.

- Klaus

Right

john curl said:
We need a class A-B 1 and A-B 2 model, B is not what a SOTA amp uses.

You can use the same model, just adjust it.

Cheers
 
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