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
United States Patent Office. 2,773,136. Patented Dec. 4, 1956. 2,773,136. AMPLIFIER. Julius Futterman, New York, N. Y.
Thanks!
One of my business partners at the time had West Sound Lab monsters and used, of course, my amps. Sounded terrific (all speakers are, of course, to someone’s taste). no issues whatsoever. Just sayin’
Edit, after some coffee, do remember back (oh, 300 posts ago, i get it :-)) that my designs are not zero output impedance. Since they do not use global feedback, there is always *some* meaningful output impedance, but also, pretty much zero chance of instability. Both often issues with large 'stats.
I forgot that the Sound Lab has adjustments on the back to allow for more bass and less treble. Anytime you see that sort of thing on the back of the speaker, its an indication that the speaker does not conform to the voltage rules. It has the adjustments to allow the unknown output impedance of the amplifier to work with the speaker (IOW they are not there to adjust the speaker to the room). So that was not the best example on my part.

Running zero feedback is a nice way to insure stability. What is the output impedance of your amp?
Tony - I can fund transcription and or digital copy of the RM/Futterman tapes. i believe those would be important historical context. Advise please.
best
Jim
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.

Of course it means bias stability demands attention, but i solved that decades ago.
:)

@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?