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回復 12735# beerboy
The notion of simplicity ties in a bit to short- or long-lived trends—I don't want to call them fads—where the emphasis in electronics has been in one area over another. When Threshold first started out, back in the Phase Linear days, high power was the item that was going to deliver the performance that everybody really wanted. The emphasis was on high power. Then, high power and very little distortion, so that static figures—getting those double-0 distortion specs—became very important to everybody. But people still weren't satisfied with that. "How come tubes still sound better?" was a very common refrain.
The focus then shifted to slew rate and TIM—low amounts of feedback and high-speed circuitry—the idea being that high-speed signals would somehow confuse an amplifier. People began building fast amplifiers and, lo and behold, quite a few of those fast amplifiers sounded significantly better. The interesting thing was that in order to achieve that higher speed, they had to make the circuits simpler. I don't think it was actually a cause-and-effect relationship. I think that for the most part the higher-speed circuits sounded better because it took simpler circuits to get high speed with stability.
However, there were some examples of very high-speed circuits out of some companies—who shall remain nameless—where they were doing 1000V/µs but everybody thought they sounded pretty bad. And tube circuits aren't so fast, especially after they get through the output transformer. The notion of measuring slew rate on a tube power amplifier doesn't make a lot of sense because you don't ever get to observe slew as such.
After that, though, the focus shifted to class-A and high current. High current seems to have been the real thing that a lot of people began buying by. In other words, they stopped worrying about what the distortion spec and the slew rate were and simply wanted to know how many amps it would put out. And we, along with other high-end manufacturers involved in the race, have been able to demonstrate how much high current we can deliver. I believe we are the champions of that, and I say that only because we've publicly demonstrated output currents on amplifiers in excess of 200 amps. I haven't seen a similar demonstration elsewhere. But in fact, we do get output currents for brief periods of time that will go up to those levels, with fairly low distortion. I've got some examples of amplifiers where the output current is ±100A sinewave into, say, a 0.1 ohm load, at about 1% distortion. Not bad at all. And there really isn't any limiting built into the amplifiers. In our latest brochure we published the curves of all of our amplifiers at 8, 4, 2, and 1 ohm, and they actually hold up pretty nicely.
There is some reason to do this. Some loads that are out there do go below an ohm. Quite a few of the electrostatic designs have been observed to hit points below an ohm. Some of the woofers from major manufacturers go down below an ohm. And when you start looking at that you can see that there's some merit to having that much current. You can also view it from the standpoint of the engineer's bias. The engineer always says, "Well, if an amplifier is going to be called upon to do say, 10 amperes, then let's just put a 10:1 margin on it." This is a very common thing. I've heard John Curl say it, I've heard other designers say it...Well, 10:1 is pretty good. That sort of thinking was being used also when people were dealing in slew rate. A 1000V/µs slew rate was, at one time, obviously state-of-the-art, but it was also being touted as "you need this!" |
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發表於 2012-5-31 11:45
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巧新淨呀.....
