马克列文森设计师John Curl 谈保险丝

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Q: Well, one of the things about Parasound amps, they are very rugged and that’s - is it an important part of your belief in amps?
JC: Well, it's not me that does that. Over the years Parasound has developed some very effective protection circuitry. It has an output relay that could be problematic in extreme circumstances. It’s kind of like a rev limiter on a car. It doesn't do anything until you exceed the redline, and then it cuts power to keep the engine from blowing. It could reduce your performance sometimes if you like to push your engine beyond the redline. It depends on what you want. Do you want to be a hot rodder or do you want your engine to hold together? I have an old Porsche and it just can’t breathe. It has a hard time just getting up to 6,000 rpm, which is it’s red line. You’re saying what am I doing here? I'd better shift because I’m not going anywhere. I also have an Acura and, man, that thing kicks in from 5,000 to 7000 rpm and I’m always going through the rev limiter at 7,000. If I didn’t have a rev limiter, it’d be gone. Parasound's amps use a very sophisticated protection circuit that they’ve or developed over the years, and basically it's the equivalent of a rev limiter. It senses a number of things and when you’re in trouble and it’s too hot it fires this circuit to open the relay and protect the amplifier and the speakers. It’s a lot better than fuses, because fuses are non - linear. They can’t help it. They are designed to have to heat up before they blow up. This heating process changes it’s resistance. The resistance invariably rises as the temperature goes up --that’s pretty much the laws of physics-- and of course it’s going to modulate. If you have a lot of current flow, even though you’re below the limit of the fuse, the darn fuse is going to modulate. Of course, this is almost impossible to measure statically. Once you put a resistive load on and a certain amount of power the fuse is going to up to it’s temperature and stay there and the resistance is not going to change very quickly, so you never know that the fuse is distorting. It only distorts getting up there and then going back down. It doesn’t necessarily distort by the time you’re ready to make the measurements. That’s one of our problems with static measurements. You just don’t know everything that you need to know.

问：Parasound放大器的性能之一，他们是非常坚固，你认为这是放大器性能的重要
组成部分吗？
JC：嗯，不是单单是我这么认为的，多年来Parasound已经开发了一些非常有效的
保护电路。它有一个输出继电器，在极端情况下可能会有问题。这有点像汽车上的
一种转速限制器。它不会有任何动作，直到你超过预定的限速红线，然后它会切断动力从而保
护引擎。如果有时你想让引擎转速超越红线，限速器的存在会降低引擎的输出性能。这取
决于你想要什么。你是想成为一个狂热的驾车人还是你希望你的发动机安全正常工
作？我有一个旧的保时捷，它的进排气性能不好。引擎升到6000转比较困难，而6000转
就是红线。你说我这里能做什么？我只能换档，因为不换不行。我还有一辆Acura，
那车在5000到7000转之间性能特好，所以我总是超过7000转。如果我没有一个转
速限制器，这车就不会存在了。 Parasound的放大器使用一个非常复杂的已经发展
多年的保护电路，基本上这个保护电路就是相当于一个转速限制器。保护电路检测放
大器的工作状态，当放大器有问题而过热时保护电路触发，打开继电器从而
保护放大器和扬声器。这要比保险丝好，因为保险丝是非线性的。这没有办法。保
险丝的设计就是在融断以前一定是热的。这种加热过程改变它的电阻。金属的电阻
总是随着温度的升高而上升 - 这是物理定律 - 而这种电阻变化就会引入信号调制。
如果一个保险丝过很大的电流，即使电流低于保险丝的额定值，那该死的保险丝的
电阻变化是会调制信号的。当然，在静态这是测量不到的。当你接上负载和功率，
保险丝温度会升到一个固定值而不会变化，所以电阻也不会变化很快，所以你永远
不知道是保险丝引入了失真。只有当温度变高变低时保险丝才会引起失真。而当你
准备测量时，它不一定会引入失真。这是静态测量问题之一。你只是不知道你需要
知道的每个方面。