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Thread: 2013 audio overhaul
02-13-2013, 11:58 AM #11
Class D versus Class AB? The sound quality difference at this stage with higher grade Class D amplifiers is a myth or a result of placebo effect. There is good and bad grades of everything.
Here is a little education.
Class B is deeply flawed because the independent positive and negative transistors do not transition without serious distortion. They are not as linear or as responsive when going from zero potential to a certain voltage. But they do perform uniformly from a running voltage to any change in voltage. Sooo, Class AB places a bandaid on the problem by applying a bias voltage so that both positive and negative transistors are 'ON' to a degree all the time, even without a signal. The two opposing voltages cancel one another. But in the process create great waste and lots of heat is generated. Now they have been at Class AB since I was riding shotgun for Wells Fargo stagecoach lines (not actually)....so it is well refined. But bottom line is Class AB is a bandaid for Class B warts. It's like the pot calling the kettle black.
There is nothing digital about a Class D amplifier. It was just the next alpha designation available. It is a pure analog switching amplifier. The better ones switch and correct at a frequency ten times the sampling rate of CDs and 30 times higher than we will hear. The filtering is so high that it is completely detached from the audible bandwidth and leaves zero switching artifacts. But in the process generates one/fourth the heat for the identical current draw. And you're listening to an MP3 format through junk D to A conversion? In an environment with 50 db of ambient noise if you are at rest and the only one in the cove? How does that Class AB sound when it's choked for voltage because it's pulling 60 percent more current to make the same power?
Triple Darrington AB is well documented to have stabilty issues with highly capacitance loads. So they add a coil to the final stage of the outputs, just before the speakers, to provide a little inductance so there is no risk of oscillation into tweaky loads. Same darn filtering device used in a Class D amplifier.
Now esoteric home HiFi companies have like Krell and Mark Levinson have adopted fullrange Class D amplifiers. Think those cork sniffers are hyper particular?
Prosound is heavy Class D on self-powered fullrange HLCD line arrays.
The Absolute Sound did a feature edition on Class D amplification with prominent home amplifier engineers including Class A, Class AB and tube advocates. With that type of attention in that type of publication, you just cannot cling to antiquated technology from a previous century.
The best ME engineers from yesteryear that once produced AB for Precision Power, Xtant, Rockford Fosgate, Phoenix Gold and Zapco, to name a few, have all adopted fullrange Class D. The companies with domestic engineering have adopted fullrange Class D. Some of the importers have not.
Let's see....Alpine, JL Audio, Hertz/Audison, Rockford Fosgate, Kicker, Wetsounds and just about any company of consequence is focused on Class D for now and the future.