Ja det är ju typiskt! jag har letat på nätet i en vecka efter svaret på min fråga och bara ett par minuter efter att jag satt mitt hopp till detta forum så hittar jag svaret själv.
tack ändå och om någon blev nyfiken så hittade jag detta på
http://www.classic-audio.com
Q: What does the "DC" designation on some components mean?
A: The "DC" designation refers to the fact that this preamp, amplifier or integrated amplifier can amplify signals over a much wider range than non-DC designs. Here is why that is useful:
The sounds that most people can hear from their stereo are created by speaker surfaces that are being forced to move back and forth by precisely controlled positive and negative surges of current driven through them by the audio amplifier. This occurs at rates of from twenty times a second, to as high as twenty thousand times a second.
For the slowest rates (20 times a second), the amplifier has to correctly amplify these slow signals; if it does not, the sound that comes out of the speaker will be different than the sound on the audio source. Many amplifiers do a fairly poor job of amplifying such slow signal changes - they are designed to cover a wide range of signals, but at the edges of that design, the amplifier's performance limitations begin to affect the signal adversely.
The reason that designs like this are marketed successfully is that most people cannot hear very well, or at all, at the outer limits of their hearing range (20 times a second, or 20 Hz, for instance.)
DC amplifiers, preamplifiers and integrated amplifiers are designed to be able to amplify signals that are much slower than the 20 changes per second that you can hear if your hearing is very discriminating. They can amplify signals at 10 changes per second; at five; at one, and even signals that don't change at all! That last type of signal is a special one called a "direct current" signal, or "DC" for short. That's precisely where the term "DC" comes from when you see "DC amplifier" or "DC Preamplifier".
This example should serve to explain the term DC a little further. If you connect a battery to a lamp, the battery steadily provides a current that does not change (until the battery runs down, of course.) A DC amplifier should be able to respond accurately when a battery is applied to an input - the current output to the speaker should then change until the amount of amplification set by the volume control is reached, and then stay there. Note that you would definitely not want to actually try this, as it is not good for the speaker at all!
The idea of a DC audio component is not to actually amplify a direct, steady current, but rather to extend the amplifier's ability to correctly reproduce a signal so far below the 20 changes per second it needs to that the 20 changes per second is no longer at the "design edge", and so benefits from the same benefits as the majority of the middle range of reproduction does.
It is interesting to note that most of the Marantz DC amplifiers have a switch on the back to actually prevent the user from applying a DC signal to the amplifier inputs, specifically because this can damage the speakers, as I described above - and no one wants that! |
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Posted - 2002/12/20 : 03:33:55
