opaqueice;164422 Wrote: > To try to answer the original question: the source (CD player, SB, > turntable) outputs some voltage signal. The ideal behavior for an > amplifier is to boost that signal by some specified factor without > distorting it. There are several things which can go wrong with that > (I'm going to simplify a bit here for clarity). > > One is if you have several sources with different output voltage > levels. In that case the amp might not be able to produce the same > level of sound from those sources, as it won't be able to boost a > smaller voltage as much as a larger. This is an issue mainly with > turntables, so if you don't have one you can probably forget about > that. If you do, you'll probably need a preamp designed to handle it. > > Another issue is impedance. When we talk about the voltage output of > the source, we mean the result we would get if we put an infinite > resistor across the output terminals and measured the voltage across > it. Now suppose instead of an infinite resistor, we put a resistor > with a finite resistnace across the outputs. Then some current would > flow, and because the source isn't perfect the voltage across the > resistor would be lower than in the ideal case. > > When you connect an amp or pre-amp to the source, that infinite > resistance is replaced by some finite impedance (which is called the > input impedance of that amp or pre-amp). If the input impedance is too > low, the source will be trying to output more current than it can > handle, and the voltage will decrease. Since impedance is a function > of frequency, the voltage will drop more for some frequencies than > others, which causes distortion. > > To avoid that you need a high input inmpedance device connected to the > source. Some power amps have high enough input impedance for a given > source, but some don't, and in that case an active preamp can help. > However if the amp by itself was fine, adding the preamp is simply > adding an unnecessary extra component, which will add some (probably > minor) level of noise and distortion to the circuit. So in that case > the best preamp is a piece of wire.
That's the best explanation of impedance matching I've ever seen. I NOW understand this concept for the first time. Thank you. -Ben -- Ben Diss SB3 -> Lavry DA10 -> BAT VK-31SE -> Halo A21 -> B&W 803D ------------------------------------------------------------------------ Ben Diss's Profile: http://forums.slimdevices.com/member.php?userid=4289 View this thread: http://forums.slimdevices.com/showthread.php?t=30852 _______________________________________________ audiophiles mailing list audiophiles@lists.slimdevices.com http://lists.slimdevices.com/lists/listinfo/audiophiles
