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In Reply to: Common misconception posted by Slider on April 21, 2007 at 13:36:01:
Does that amp run in pure class A?
Follow Ups:
That's kind of the point, there isn't a real definition. But yes, it is advertised as a pure class A amp, and doesn't differ in that regard from many other similarly advertised designs from big and small companies ...
So you won't be submitting a correction to Wikipedia?
just not necessarily right either :-)"Pure" is really a modifier that hasn't much meaning in this context. It might have been used at one time in an attempt to separate the shadier advertisers from the more consumer friendly advertisers, but nowadays it is just an advertising term. In the end, not many amplifiers, regardless of class-A "purity", consume the same power at idle as they do at full power, and at all loads. Bias levels change and adjust, and banks of transistors still change bias in most push-pull designs at high power levels when they aren't needed, unless it's just a resistor biased single-ended design like some of the very low power class-A amps.
The definition of Class-A is that the devices conduct current during 360 degrees of a sine wave cycle. This does not necessarily mean that the input power requirements are steady during variations in the output power. The belief in this relationship is due to circuit designs that are very old. These older designs generally have a bias point that does not intentionally change as the power level changes. Unfortunately this is not a very efficient design from a power consumption perspective or from a power vs. device cost perspective.As designs have developed over time techniques have been developed and utilized that allow compliance with the definition of Class-A that improve power efficiency and allow greater power output from a fixed number of devices.
"Power Consumption (idle) 175watts
Power Consumption (full rated power @ 8ohms) 720 watts
Power Output 20hz - 20Khz @8ohms 150 watts RMS per channel (both channels driven)"
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