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Old 24th July 2009, 06:10 AM   #461
PMA is offline PMA  Europe
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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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Old 24th July 2009, 06:25 AM   #462
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Pavel, it is valid for a push-pull stage biased in class A, but not valid for a stage designed for class A, like in my Tower amps.

As soon as I designed it and proved the concept, the rule of thumb is no more valid. It is not a problem anymore, at least it is not unavoidable problem.
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Old 24th July 2009, 06:31 AM   #463
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Anatoliy, that's why I emphasized the push-pull both in text and the image.
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Old 24th July 2009, 06:43 AM   #464
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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.

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Old 24th July 2009, 06:48 AM   #465
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Quote:
Originally posted by PMA
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 . Really!


jd
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Old 24th July 2009, 06:54 AM   #466
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Quote:
Originally posted by janneman



Nice to see the freq doubling confirmed
Quite difficult task to force the power to get negative
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Old 24th July 2009, 07:29 AM   #467
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AD8052 looks interesting, though +/-5V only...
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Old 24th July 2009, 09:31 AM   #468
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I noted by
John Curl's Blowtorch preamplifier
that many "death links" are to find, e. g. from Richard Perez (Justcallmedad). Also about http://www.archive.org/web/web.php I don't get this one.
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Old 24th July 2009, 11:26 AM   #469
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This is for Push-Pull Class B.
I had to split the document; the file size was too large.
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Old 24th July 2009, 11:29 AM   #470
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Page 4

I had to reduce the size of this page so the images are not easy to see.
I can post them separately if there is any interest.
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