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Are all amps being built wrong?

The power amplifiers that drive our loudspeakers are mostly built as a low impedance voltage source. They have always been ... but why?

Loudspeakers have a (greatly) varying impedance over the frequency range. A current drive amplifier would eliminate the issues that stem from this varying impedance, and at the same time make discussions about esoteric speaker cables that strive for optimal R, C, L superfluous. Although there still would be these un-measurable ’this (very expensive) cable sounds better’ debates and opinions ... and that’s OK, that’s part of the fun. :)

So ... why are amplifiers not built as a high impedance current source?

This is an interesting read: https://www.current-drive.info/
rudyb
itsjustme
682 posts
 
oops, very late to reply to @atmasphere

Output Z of the amps, depending on model is around .1 - .2 (rarely this high) ohms. Small but very clearly not zero.
And yes the stability is a very big plus.
Of course it means bias stability demands attention, but i solved that decades ago.

atmasphere's avatar
atmasphere
11,851 posts
 
Of course it means bias stability demands attention, but i solved that decades ago.
:)

holmz's avatar
holmz
2,328 posts
 
@atmasphere 
Running zero feedback is a nice way to insure stability. What is the output impedance of your amp?

I was talking to a fellow yesterday that said that the feedback of the Prima Luna was too high.

Do you have thoughts on that?
jtgofish's avatar
jtgofish
515 posts
 
All amps should come with variable feedback.
bifwynne
2,206 posts
 
Ralph (Atmasphere) posted: 
If you add a resistor to the output of a solid state amp it will indeed simulate some sort of tube amp that uses feedback. Most transformer coupled tube amps with 15dB of feedback will act as a pretty good voltage source. You might have to play with the taps on the output transformer. Between Voltage source and Current source there is Power Source, which is how a tube amp will behave if it has no feedback or if it has voltage and current feedback of equal amounts.

I think Ralph is right on.  My ARC Ref 80S is a transformer coupled tube amp that uses 14db of negative feedback.  And I do **play** with the taps to get the best sound.  At this point, I have settled on the 8 ohm taps, which I believe have an output impedance of approximately 1 ohm.  The DF is 8 if the amp is coupled to an 8 ohm speaker off the 8 ohm taps.

As to comments made by others, I believe that it is correct to say that matching my amp (or one like it) to a speaker that was designed and voiced to be driven by a constant voltage source amp is a bit of a tone control.  To some extent the amp's voltage output will vary to some degree as a function of speaker impedance, which in turn, will vary with frequency.  

All that said, I like the sound of my amp/speaker combo, ... tone control and all.  Ironically, I surmise that between room affects which probably boost the bass a bit and and the tone control affects of the amp which soften the tweeter/high frequencies, the overall frequency response and sound is musical and pleasant.  Just my opinion. 

BIF

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