Are all amps being built wrong?
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"! How useful would a current drive amp be with a 1 ohm speaker that has a flat impedance? |
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!This statement is false. No Futterman amp ever had anything like 60dB of feedback!! The most any had was more like 20dB, and because the amp had very wide bandwidth, oscillation (caused by its phase margin being exceeded by the feedback) was sometimes an issue. So to your closing comment here- they are well-known to **not** be stable into complex loads. If you doubt any of what I'm saying, just for the record I've been manufacturing OTLs longer than anyone else on the planet (over 46 years); I'm not being hyperbolic. |
This is an interesting article on the subject, © 2019, Rod Elliott (ESP) https://sound-au.com/articles/current-drive.htm#s1 One of the conclusions (scroll to the bottom of the long article): "There have been many claims over the years that current drive is the best, and some may claim it's the only) way to drive loudspeakers, as it reduces distortion and allows the speaker to work the "way it was intended". While there is some discussion of this on the Net (see [ 2 ] as an example), there is little real evidence that the benefits are anywhere near as great as claimed. Tests I've run have shown little improvement, and this is expected given that loudspeaker systems and the drivers used therein are designed specifically with the understanding that they will be driven with a voltage amplifier. By definition, that means the output impedance is low, always below 0.2Ω, and often much less." |
This is an interesting statement: " Tests I’ve run have shown little improvement, and this is expected given that loudspeaker systems and the drivers used therein are designed specifically with the understanding that they will be driven with a voltage amplifier." However small, apparently there is an inprovement with current drive. Which could grow larger when speakers would be specifically designed for current drive. One can wonder why it is not used more often ... any improvement is good, even more so knowing people are willing to spend thousands on their (power, speaker, interconnect) cables alone to gain just a very minute improvement. |
