Quote:
Originally Posted by wlai
I'm guessing that preAmp is a current multiplier, and so is a headphone amp, and a power amp is a voltage multiplier
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No, assuming a headphone amp with voltage gain, such an amp is a voltage amp just like a preamp is. It also happens that headphone amps usually have about the same amount of gain (about 5x to 10x) as the line stage preamp.
However, headphone amps must be able to drive must lower impedances than a preamp (headphones are usually anywhere from 16 ohms to 600 ohms, where a preamp would only need to drive the input stage of a power amp, in the tens of Kohms or more range). So, better headphone amps typically also have a current amplifier output stage with lower output impedance and higher output current drive capability than preamps.
It turns out this lower output impedance and extra current capability is beneficial even when serving as a preamp. Interconnect cables have capacitance, and the longer the cable is, the higher the capacitance. Low output impedance and high current capacity reduces the adverse effects of such capacitance. The output impedance of the amp and the cable capacitance forms an RC low-pass filter, so if the impedance is high, and the cable is long, then there could be high frequency loss and phase shift. Fast swinging signals into a capacitive load require a lot of charge current to avoid slewing, so the higher current capability of headphone amps has an advantage. Last but not least, headphones are sensitive devices, so the amp must have very low noise floor. Low noise is also an important requirement for a preamp.
These factors are why a good headphone amp can also make an excellent preamp. Just add multiple inputs and a selector switch.
Quote:
Originally Posted by Freq Band
Is there a possibility that a power amp will not like to see "too much" current ?
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If you're talking about the drive current from the preamp, the answer is no. The current delivered is purely detemined by the impedance of the input stage of the power amp. Even though the preamp (or headphone amp serving as a preamp) may have very high current capability, the high input impedance of the power amp will limit the amount of current to a miniscule amount. Simple Ohm's Law. I = V / R, where I is the current, V is the output voltage of the preamp at any given instance, and R is the input impedance of the power amp.
