Hello,
I was considering to try to buy one set of amplifire boards from aliexpress, they specify the output power both in Class A and Class AB.
In this type of amplifires, is there a switch where one can switch between the two classes, or how does it work, do you know?
I was considering to try to buy one set of amplifire boards from aliexpress, they specify the output power both in Class A and Class AB.
In this type of amplifires, is there a switch where one can switch between the two classes, or how does it work, do you know?
Yes, bias spreader could allow you to +-easily switch between A and AB.
But typically you need to drop supply at order of twice in A-class bias for keeping power parts in safe operating conditions.
But typically you need to drop supply at order of twice in A-class bias for keeping power parts in safe operating conditions.
Thank you BesPav,
Why do you think they inform the power rating in both class a and class ab on these boards, do you think they can be configured one time fo all into one of the classes, or do you think one can switch between the two classes all the time?
Why do you think they inform the power rating in both class a and class ab on these boards, do you think they can be configured one time fo all into one of the classes, or do you think one can switch between the two classes all the time?
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.
Artistic license. An amp advertised that it can deliver its first watt (or whatever the figure may be) in pure Class A sounds much more attractive than describing it as a Class AB design.
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 think,if memory serve well,that Bonsai's SX would be a class A or a class AB amplifier selectable by switch.
Hello all,
Thank you very much.
So is i correct understood that when i play low volume, the amplifire will run in classe A, but when i increase volume...it wil automatically change into classe AB?
Thank you very much.
So is i correct understood that when i play low volume, the amplifire will run in classe A, but when i increase volume...it wil automatically change into classe AB?
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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