Scroll down to “Adjustable biasing”:
https://www.electronics-tutorials.ws/amplifier/class-ab-amplifier.html
Mostly all push-pull AB amp could be tuned to full A-class and vice-versa.
But keep your attention to heat dissipation.
https://www.electronics-tutorials.ws/amplifier/class-ab-amplifier.html
Mostly all push-pull AB amp could be tuned to full A-class and vice-versa.
But keep your attention to heat dissipation.
What I think they meant - class AB amplifier has got some class A operating area. Normally it's relatively narrow, providing class A operation up to some low power limit - like 1W or so. It may vary, depending on the overall quiescent current of the output stage (OPS).
As soon as you increase the volume, you reach the point where the OPS halves start going off - then you are in the class B area.
So, for a class AB you can specify 2 power levels - class A power (normally it's relatively low - depends on the OPS bias level), and class AB power - which is a full-swing power of the amplifier.
Agree.
You may do it simply by increasing idle current beyond usual so you have more power in the Class A region.
It will increase dissipation, specially idle dissipation, but won´t change full power dissipation a lot if you don´t overdo it.
I guess (should do the Math in every case) that, say, biasing a 100W amp so the first 10W are pure Class A (instead of the usual 1 W or less) should provide most of the benefits without too much trouble, beyong increasing heatsinking somewhat, definitely way less than going Class A full tilt that is.
And if power supply is generously rated for full Class AB power (as it should), that extra waste of idle power should be relatively easy to handle.
Of course, amp will switch between classes all by itself, without any complicated circuit to do so
You may do it simply by increasing idle current beyond usual so you have more power in the Class A region.
It will increase dissipation, specially idle dissipation, but won´t change full power dissipation a lot if you don´t overdo it.
I guess (should do the Math in every case) that, say, biasing a 100W amp so the first 10W are pure Class A (instead of the usual 1 W or less) should provide most of the benefits without too much trouble, beyong increasing heatsinking somewhat, definitely way less than going Class A full tilt that is.
And if power supply is generously rated for full Class AB power (as it should), that extra waste of idle power should be relatively easy to handle.
Of course, amp will switch between classes all by itself, without any complicated circuit to do so
I have a Electrocompaniet AW65 power amp, believe that it running under class AB mode.
If i were to transfer the entire pcb onto a much bigger heatsinks, can i run it in full Class A mode by just cranking up the bias current ?
Will these method works?
I will be happy if i can have 20W in pure class A from this amp.
If i were to transfer the entire pcb onto a much bigger heatsinks, can i run it in full Class A mode by just cranking up the bias current ?
Will these method works?
I will be happy if i can have 20W in pure class A from this amp.
The power supply will have to be uprated too, this will give you a good idea of what can be done 25W Class-A Power Amplifier
I'm currently building Bonsai's KX amplifier and it does have the option to play in class A or class AB.
A fair number of "Class A" advertised amplifiers are in class B portion well before they reach their rated power. A 100W Pure Class A amplifier would be one humongo amp. There are some that stay Class A at 8 ohms up to clipping, but they're a bit rare. And run them at low enough impedance and they transition to Class B.
The only sure way to stay in Class A up to clipping is to go with a single ended amp, as it can't transition to Class B. But that's not exactly an advantage.
The only sure way to stay in Class A up to clipping is to go with a single ended amp, as it can't transition to Class B. But that's not exactly an advantage.
Nobody seem to answer this particular question
You're right - at the low volume you stay within class A operation.
As soon as you increase the volume - you enter class AB territory.
If you increase the bias, class A area becomes wider, allowing class A operation at higher volumes.
Picture below is a very schematic presentation of the principle.
The signals have different periods, but never mind - we are interested in their amplitude right now
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