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Re: Why using line stage........

IMO dynamics come from appropriate gain and correct impedance matching.
With today's 2 V CD outputs, resistive passive preamps can output enough voltage to saturate the power amp's inputs (so their gai structure is OK), however, they usually have high output impedance.

One can make the analogy that passive preamps do not have the torque to rev up the engine, but given enough time will reach high RPMs (loudness).
What one neeeds is some means to lower the output impedance to enable the output stage to sink current(torque) and voltage(speed) into the power amp input.
There are two ways to accomplish this: a low impedance ative line stage or a transformer volume control, which lowers impedance by a factor of as it reduces gain by a factor of 2(do a search on TVC).
Passive preamps based on resistors, potentiometers or switched attenuators will usually have about 5 K output impedance, way too high to really make a 10 K power amp input jump up and shout.
I hope this helps
Carlos



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