Current amp vs Voltage amp

A note on terminology: Unless there are some extremely unusual exceptions out there, all audio power amplifiers amplify both voltage and current, so the terminology in the subject line of the thread is a bit misleading.

Solid state amplifiers having near zero output impedance are sometimes referred to as being voltage sources, meaning that for a given input voltage their output voltage will remain constant regardless of load impedance (within the limits of their capability). Referring to them as being voltage sources is accurate terminology, to a very close approximation. (The reason it is a very close approximation, rather than being exact, is that no real world amplifier can have an output impedance that is exactly zero).

Tube amplifiers, having significant output impedances, are sometimes referred to as being current sources, which strictly speaking would mean that for a given input voltage the current they output would remain constant regardless of load impedance (within the limits of their capability). That is NOT accurate terminology, except in the extremely loose sense that their output current will vary LESS as a function of load impedance than in the case of an amplifier having near zero output impedance.

It may be helpful to read this Wikipedia writeup on the voltage divider effect. In the first figure, consider Z1 as representing the output impedance of the amplifier, and Z2 as representing the impedance of the speaker, which will be different at different frequencies.

Regards,
-- Al

Al, my take on this, is that on speakers with varying impedances(all?), such ss amps are more likely to provide more linear output from those speakers. Please correct me if I'm mistaken.

Hi Unsound,

I suspect it to be true that more often than not speakers having widely varying impedances will provide flatter frequency responses when driven by solid state amps. But if so, that would simply be because more often than not speakers are designed and voiced with the expectation they they are most likely to be used with solid state amplifiers.

But there are certainly a great many speakers having widely varying impedances that will do better with tube amps than with solid state amps. Many electrostatics are notable examples, along with a goodly number of dynamic (box-type) speakers.

The effects of amplifier/speaker impedance interactions are, of course, just one of a great many factors affecting the frequency response and tonal balance of a speaker. Which kind of amplifier stands the best chance of being optimal after all those factors net out depends, as Atmasphere has said in similar threads in the past, mainly on the intentions of the designer.

Best regards,
-- Al

Al thanks or the informative posts

Loudspeaker's interface likewise: variabilities-

http://www.inner-magazines.com/news/345/57/Current-please-no-voltage/

Al, the wouldn't sensitivity of the speaker vary along with the impedance?