jukes
Full Member
Posts: 40
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Post by jukes on May 2, 2004 13:06:25 GMT -5
i have no idea
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Post by Ol Geezer on May 2, 2004 13:14:49 GMT -5
It has to do with power being on at all times, whereas a Class AB alternates power on and off. That said, here is a rather complex definition I just found for you on the Internet: A class A amplifier is defined as one which is biased to a point where plate current in all the output devices flows for the entire 360 degrees of an input cycle, at the full, unclipped output of the amplifier. This is typically done by biasing the output stage halfway between cutoff and saturation, with the plate load impedance to an appropriate value that gives maximum undistorted output power. This is the least efficient method of amplification, because the output devices are dissipating maximum power with no input signal.
For audio amplification, a class A amplifier can be either single-ended or push-pull. Now, you might be thinking, how can a push-pull amplifier be class A? Doesn't one side amplify half the waveform and the other side amplify the other half? Isn't this why we use a phase splitter? These are common misconceptions. You can, indeed have a true class A amplifier that operates in push-pull mode. Amplifier class has absolutely nothing to do with output stage topology. If the output tubes on either side of a push-pull pair are biased in class A (halfway between cutoff and saturation), then the current in each side will still flow for the full 360 degrees of the input cycle, just in opposing directions. As one tube's current increases from the midpoint, or idle, bias current, the other tube's current is decreasing by an equal amount. The output transformer sums these oppositely-phased currents to produce the output waveform in the secondary winding. As one side reaches saturation, the other side reaches cutoff, just as they would in a single-ended class A amplifier. Neither side cuts off at the full, unclipped output power of the amplifier. The output power of a push-pull class A amplifier is exactly twice the output power of a single-ended class A amplifier operating under the same conditions of plate voltage, bias, and effective load impedance.
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jukes
Full Member
Posts: 40
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Post by jukes on May 2, 2004 13:23:34 GMT -5
thanks for the reply.but does that mean my amp @40, watts is as loud as a my fender ultra chorus 65 watt amp?
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Post by zep on May 2, 2004 13:27:28 GMT -5
Uhh, I'm still lost, but oh well. Class A amps are generally rather expensive so I guess it doesn't matter that I don't know what that "definition" is talking about.
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Post by Ol Geezer on May 2, 2004 14:53:57 GMT -5
Uhh, I'm still lost, but oh well. Class A amps are generally rather expensive so I guess it doesn't matter that I don't know what that "definition" is talking about. Exactly. That's why I stated it was complex. I don't claim to understand it all either, but I know how to copy and paste!  Apparent loudness between two different types of amp's ratings can't be easily compared, since the rest of the circuits and components may differ as well. Class A amps are by design less efficient but, because of that, have less distortion. They're pulling full power all the time, with clean output available if needed but generally being wasted. It's kind of like taking a dragster to the market and keeping it idling while you shop.... |
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