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In Reply to: RE: there are some amps posted by Tre' on February 07, 2025 at 11:33:15
Please see the picture
Follow Ups:
There is more to Class A than the short definition.
"In a class A amplifier current flows for 360 degrees"
A class C amplifier meets that definition, there is always some leakage current flowing.If you take the time to read the Radiotron Designer's Handbook and Tremaine's Audio Cyclopedia (and read beyond the short definition) you will see that with all of the examples of Class A (and a lot of the discussion of Class A) the bias point of in the middle of the "most linear part of the dynamic curve". You will also learn that with Class A the input is limited as to not drive the device into the non-linear regions (saturation and cutoff). Again, with Class AB the device is ran into the non-linear cutoff region (if not biased there to start with).
I don't know how you (or anyone) can call the circuit you showed Class A.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 02/07/25
This is from stereophile review
"Looking inside the KSA-250, the emitters of the 12 pairs per channel of output-stage transistors appear to standing on series resistors of nominal 1 ohm value. The average voltage drop across these resistors was 110.5mV, implying a standing bias for each of 110.5mA; ie, a total of 1.33A. This will give a maximum power for true class-A operation into 8 ohms of 28.5W (14.5dBW) rather than 250W."
Most Class AB amplifiers are bias low. So low as to be in the non-linear cutoff region at idle. Even though there is some power while both devices are conducting all the time, that power can not be considered Class A power. A device biased that low is not "operating in the most linear part of the operating curve".
If there is a Class AB amp that is biased high and does have some operation (or even a lot) where the devices are both conducting all the time and not dipping into the non-linear cutoff region, then that is closer to Class A but again, the devices in a Class A design are biased in the middle of the *most linear* part of the operating curve (for the device choose). The devices in a Class AB amplifier are not.
If the KSA-250 can output 250 watts but only 28.5 watts with the devices conducting all the time then it is a Class AB amplifier and it is biased as a Class AB amplifier (lower than the mid point between cutoff and saturation) and regardless of what the review says, none of it's power is true Class A power.
None of what I am saying is hard to understand. Class A amplifiers produce Class A power. Class AB amplifiers produce Class AB power.
Class A biased devices are idling at half the max current, Class AB biased devices are idling at something less than half the max current.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
in the forums?
If you are asking about the manufacturers that will tell the buyer that their amplifier operates in Class A for a certain amount of watts then it operates in Class B for the rest of the watts then I have to remind you that marketing is an important part of any business.
It is just easier to explain it that way rather than trying to explain that it is not really Class A, it just sort of acts like Class A.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 02/08/25
I don't need to ask you about anything.
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