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I was considering the SEX amp for my midrange, but wasn't sure if it could be used with out a tube preamp. But I just saw that someone was using it with a CD player. What voltage and impedance can this amp operate with?
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The input impedance is 100 kOhms, and there is a level control, so I can't imagine that you would have any problems. Most any line-level audio device should be capable of driving 100k, and, if the level is too high, simply reduce the level control on the SEX.On the other hand, if your crossover does not put our enough level, that could be a problem. So, if you can scrounge up specs on your crossover, then post them here, and I'm sure someone will be able to tell you for sure.
The crossover is a marchand 3 way with Xm-9 boards in it. The output specs are; ouput load capability 2KOhm, output impedance 50 ohm. That is all the info that I have.
Since the SEX input impedance of 100k is larger than the minimum load impedance of 2k (!) there should be no problem.
I'm not sure what 'output load capability' means exactly.
A great source of confusion - good question!Any signal source functions as a voltage source in series with a resistance, called the output resistance. The load has a resistance also. In modern designs, the source resistance is made small relative to the load resistance. This preserves most of the voltage, independent of the actual load resistance.
The source can put out a certain maximum voltage, and it also has a certain maximum current capability. To stay within the current capability, the load resistance must be larger than some value. For example, the Foreplay can produce a maximum of 20v, and its cathode follower cannot produce more than 2mA, so its specified minimum load impedance is (Ohm's Law) R = V/I = 10k ohms. This minimum load resistance is still much larger than the equivalent internal source resistance, 800 ohms for the Foreplay. The Marchand is specified to have 50 ohms internal resistance, and be able to drive a load of 2000 ohms or greater.
Note that all this has nothing to do with "matching" resistances! That idea comes from the early days of the telephone business. If the source has no current limit, then the most power that can be extracted from it occurs when the load resistance equals the source resistance. This was important when telephones did not have amplification - the power generated by the microphone was the only power available for the earpiece, so you had to couple as much as possible to the earpiece in order to hear anything. Once the telephone system acquired tubes, that was no longer necessary, but at the same time lines became longer. Long lines (over a mile or so) have reflections unless the source resistance, line characteristic resistance, and load resistance are all identical. So matched resistances were still needed by the phone system.
OK, that spec makes sense now! Basically, they are using different phrases to mean 'output impedance' and 'minimum load impedance', if I follow you correctly.I have read a bit of history on the early telephone systems, and always marvel how those engineers figured out the balanced line, transmission line principles. impedance matching, etc., way back then. I guess necessity is a mother!
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