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I want to use a single preamp to feed multiple amplifiers. From what I understand, the limit is in the output impedance of the preamp and matching it with the input impedance of the amps. How important is this matching? Is it better to have a preamp with low output impedance for some reason? What's the difference?
Follow Ups:
If you are feeding multiple amps, the preamp sees all those loads in parallel, lowering the working impedance that it sees. In addition, each of the amps sees the other as a parallel load so, if they vary considerably, one can shunt the other.
In Reply to: What does in/output impedance mean? posted by Mike D on March 16, 2004 at 21:06:20:
Output impedance is analogous to the "torque" of an engine. A low output impedance means that the amplifier can deliver lots of current without a sag in the voltage. (Just as a high-torque engine can drive a difficult load without slowing down.) If the voltage sags, you will get rolled-off highs and bass, and poor dynamics. Generally, you like to have an output impedance that is about ten times lower than the input impedance of the next stage. If your input impedance is 100 or 200 times higher, that's OK.
Input impedance shows how much current you have to deliver to maintain a certain voltage. High impedances are normally "easy" loads, ie take less current, while low impedances are "difficult" loads. For example, your speakers have a nominal impedance of about eight ohms. They are very "difficult" to drive, which is why you need a big power amplifier. A power amplifier typically has an output impedance of 2 ohms or less.Sensitivity shows how much input voltage is necessary to drive the amplifier to its full output. For example, if you have a 100W amplifier but it needs 10 volts input to reach full power, but your source only does 1V max, then your amplifier will never output more than one watt. Most any preamp can output 2V or more, so any amplifier with a sensitivity of 2V or lower to full power should be fine. With a highly sensitive amplifier and a preamp with substantial gain, you may have a problem with too much gain. In this case you can't turn the volume knob past 9 o clock or so.
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In Reply to: Re: What does in/output impedance mean? posted by fred76 on March 16, 2004 at 23:56:07:
> > For example, a digital source of 30 ohms drives an input of 100k (passive line controller), will there be any roll off at the frequency extremes compared to a 10k input?> >
If it was good with a 10k load, it will also be good - or better - with a 100k load. Big load = "easy" load.
Lower on the preamp is better. Higher on the amp is better. 10 to 1 is the rule of thumb. Someone more knowledgeable should chime in on the multiple amp issue. If mismatched, you can make a good sounding amp sound like crap.Did you ever read where guy A said amp XYZ sounded awesome and then guy B chimes in and says that he heard amp XYZ and it sucked all the life out of the music? It could have been a number of things, but one of them is an impedance mismatch.
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