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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
697 posts
 
Mainly because speakers are designed to be driven by a low impedance voltage source.
Aside from what i already wrote, here's also the practical issue.  A low impedance, hgih current amp will drive anything.  Others might (might) sing with speaker A and suck with speaker B. You know, like lots of high end :-)
I'm always fascinated by this. I cam plug my amp into about anything and it will work very well and sound very good. Will it produce some synergistic, euphonic magic effect? Nope.

atmasphere's avatar
atmasphere
12,405 posts
 
Aside from what i already wrote, here's also the practical issue. A low impedance, hgih current amp will drive anything.
This isn't quite correct, just so you know. Try putting your amp on a Sound Lab ESL sometime. That speaker is 32 Ohms in the bass and maybe about 2 Ohms at 20KHz (depending on the position of the Brilliance control). Most voltage source amps tend to sound too bright on this speaker; they struggle to make power at bass frequencies. Its MO isn't based on the Voltage Paradigm. Anytime you mix the two paradigms (Voltage and Power) you are at risk of a tonal anomaly.


SETs and other zero feedback tube amps are not meant to be used with difficult speakers (and I argue that no amp should be used with such speakers since the last thing you want to do is make any amp work hard for a living- it will make more distortion which is audible). So no amp can really work with all speakers.
jasonbourne52's avatar
jasonbourne52
2,863 posts
 
Because a current drive amp is only useful with a speaker that has a flat impedance. Otherwise the amp will act as a tone control and follow the dips and peaks of the speaker's impedance curve. This can hardly be called "accurate"!
jasonbourne52's avatar
jasonbourne52
2,863 posts
 
Look up Ohm's Law!
jasonbourne52's avatar
jasonbourne52
2,863 posts
 
Julius Futterman solved the tube amp feedback problem by eliminating the output transformer. His OTL amps can have 60 db feedback with low output impedance and low harmonic/IM distortion. Yet remain 100% stabile into complex loads! The drawback is that they are best used with speakers that are 8 ohms and up due to the fact that power/watts declines into low impedances - but rises with impedance increase!
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