"Current feedback" suffered from a change of meaning at the beginning of eighties. The new meaning describes an input built with a push-pull of transistors instead of a single one but works in the same way. In a CFA, the control of the amplifier is just controlled by the voltage beetween base and emitter of two transistors instead of one.
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It's 99% moot, though. All else being equal, let's say that 100 years ago, engineers developing amplifiers with cutting edge tubes / valves, flipped a coin. If it landed 'heads', they built voltage amplifiers. If it landed tails, they built current amplifiers (or ones with a "current drive" output stage, to be clear).
The ones building current amplifiers would have a much higher rate of going out of business, simply from angry customers returning broken hi-fi sets and claiming that everything was fine and suddenly the bad amplifier broke their speaker. Another mystery solved! 😉
The ones building current amplifiers would have a much higher rate of going out of business, simply from angry customers returning broken hi-fi sets and claiming that everything was fine and suddenly the bad amplifier broke their speaker. Another mystery solved! 😉
^^
That's not to detract from your tech point, @newvirus2008 as I'm sure the switching scheme could be repurposed in some interesting ways.
Nope. Still not getting suckered in. Nearly all of the world's speakers suffer from same problem of inductance modulation, with only stop-gap solutions like passive chokes occasionally used in the "high end" niche, and these guys come up with ultra-advanced resonant blah switching solutions for 0.0001% distortion, yet still force the actual speakers to run at 1% HD and high IMD and hysteresis.
Even their own reviewers are like, "brah, this better-than-ever voltage drive is making my ears bleed. Throw me a bone this century!"
That's not to detract from your tech point, @newvirus2008 as I'm sure the switching scheme could be repurposed in some interesting ways.
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Yeah amplifiers are very uninteresting, almost as ideal as possible. Manipulating circuit impedance is where the all fun is, and in better drivers, and in loudspeaker system design in general. Amplifier is there in the chain but one of the least problematic things, just use the best one you like and that's it. Still, the performance can be manipulated further as it is not the amplifier electrical output we listen to but sound pressure waves in air in some room.
Still, amplifier is part of system, and if some particular amplifier gives better performance with the rest of the system then that's it.
Still, amplifier is part of system, and if some particular amplifier gives better performance with the rest of the system then that's it.
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Well, here's some help. A simple simulation using hysteresis switching, unconditionally stable all the way. The opamp has a voltage swing capability of +/-100V. The current pushed is 5A peak. Simulation step time is 100ns. Enjoy !....I have to get off my beach bum *** to re-learn LTspice ....
Come on, man, people have kids to feed and they need to sell something to be able to do that.
Yes, almost any amp will do as long as it has the volts and the amperes for it. Now, if it does all that very well then congrats, that's it.
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Agreed, Novak's still good -sadly overlooked after Thiele & especially Small emerged, although in most respects they were simply extending what he had previously done (which was loosly associated with Beranek, & in turn a major step forward from Thuras's foundations). I can't say I've ever found anything wrong with Beranek or Thuras's work within the framework of their respective eras though -we can find issues today, obviously, but they didn't have the advantage of hindsight & were heavily pushing the then-state-of-the-art. Ted was a very good theortician; I gather from some who worked with him that the practical engineering side wasn't his preferred field though & he tended to heavily lean on the production engineering teams to actually implement what he was working on on paper, so as is usually the case it didn't always chime perfectlyMy work was based on another guy(s?) whose name I can't remember. Peter Fryer told me that Novak probably had the correct maths and I spent 2 days proving that his sums were the same as mine .. a Herculiean task as I neber wen 2 skul and kunt reed en rite
Beranek, Jordan & Thuras were red herrings. I wasted a LOT of time trying to make sense of Jordan as he seemed to be on the right track.
Absolutely -no subsitute for hard data.
Hi kgrlee,
thank you for the answer.
Kindest regards,
M
thank you for the answer.
As I understand it, you are looking for a universal amplifier, not one designed for a specific driver.
Kindest regards,
M
Current drive isn't particularly desirable at low frequencies because of distortion due to variations in BL with excursion - which voltage drive mitigates by automatically varying drive current to oppose the variations in motive force (using back-emf). Also, there's the problem of impedance peak at primary resonance, fs.
If fs and system Q are known, then it's possible to compensate for the resonant peak when current-driven - but they would need to be very stable for this to work (so, suspension compliance would need to be very stable over time).
As for BL variation with excursion, this would have to be minimised for a driver intended for current drive.
If fs and system Q are known, then it's possible to compensate for the resonant peak when current-driven - but they would need to be very stable for this to work (so, suspension compliance would need to be very stable over time).
As for BL variation with excursion, this would have to be minimised for a driver intended for current drive.
Have you built this beast?
If not, can you post the LTspice ASC file with all the device models please?
There's loadsa stuff which looks good in theory but getting something to work in real life is often (always?) a MUCH longer process.
I've been trying, on and off, for a Current Drive amp over at least 4 decades and not come up with anything that I consider good & easy to build.
Novak had the right equation but didn't use it to get useful design procedures. No insights
Neither presented or even hinted at sensible procedures to design ported boxes.
I beg to differ. I was a disciple and took a long time to see his maths was wonky. He certainly had insights. But you should check his 'maths' very carefully
But these are ported boxes. Closed boxes are much simpler. The first accurate theory I saw was Great Guru Baxandall in 1968
https://keith-snook.info/wireless-world-articles/Wireless-World-1968/Low-cost High-quality Loudspeaker.pdf from bottom of page 317
Ported boxes had to wait for Thiele though I think his first paper (in Australia) was around the same time.
We developed our maths for vented boxes in the 70s but it took some time to realise they were equivalent to Thiele ... and that Jordan was wonky
Apologies to yus Current Drive aficianados as all the above is about Evil Voltage Drive
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Offering an extreme example with outrageous resistance relativity really does little to prove a point
And then, 'manipulate' means going straight back to crossover design or line level DSP.
Here is some info.
It is worth noting that 'flat impedance' does not necessarily equate to flat frequency response.
https://www.stereophile.com/content/magnepan-lrs-loudspeaker-measurements
Use both if needed in the application: passive parts to manipulate impedance to reduce distortion and DSP to have independent control over frequency response. Of the shelf drivers and amps while reducing acoustic distortion with same mechanism current drive amplifier would do it, you could use a resistor in series, or cheap long cabling, opposite to traditional hifi myth and marketing tactic. It would be more elegant to use inductor though.
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One possible solution could be that the excursion be kept below 50% of Xmax, where the BL product is likely to be more linear. However, this would require an oversized driver.
Maybe an adaptive system that calibrates itself every few days to keep up with the drift / ageing of the components will do ? However, all these complications make the 'current drive amplifier' look like a very simple exercise !!!
I haven't built it but it should work, as the technique (called hysteretic current control in textbooks) is already being used in many SMPSes and motor drive systems. Although I don't use LTSpice, all my parts are generic and are therefore easily available within any of the SPICE(s) that exist.
Well, that makes you an old timer with very strong fundamentals and significant experience, which is usually a good advantage while trying something new.
Think 1V / 1 ohms in place of 1kV / 1kohm, if that proves the point.Offering an extreme example with outrageous resistance relativity really does little to prove a point
I really cannot follow all the discussion concerning a worse sound with current drive in the bass in comparison with voltage drive. This is all theoretical discussion I cannot find in my auditions.
I listened to five loudspeakers in closed and open boxes with current drive and it sounds always better in the bass, too. More articulate, only more correct. Even systems in small reflex boxes show better impulse response in the bass.
Current drive helps my crossoverless fullrange speakers to sound several classes better - a leap forward in sound - than I could imagine an amplifier can do that to boxes.
I listened to five loudspeakers in closed and open boxes with current drive and it sounds always better in the bass, too. More articulate, only more correct. Even systems in small reflex boxes show better impulse response in the bass.
Current drive helps my crossoverless fullrange speakers to sound several classes better - a leap forward in sound - than I could imagine an amplifier can do that to boxes.
^ Room can easily make +-10db variation in response at listening spot. If there is peak in system Q due to lack of electrical damping, it likely doesn't differ in anyway what the room already does. However, if you want to have it even better then you might have some method to mitigate some of the room effects in which case the Q could be more audible. In which case you might have to do something about it as well. One could also say that multiway speaker sounds better than fulrange.
Have you tried measuring any speaker with current drive amp? Take the frequency response, then use voltage amp and match system response with DSP. Still better sound? As long as frequency responses differ it's hard to say what makes a difference. In theory the current drive, or reduced distortion, ought to give better sound, especially on small drivers in wide bandwidth application.
Have you tried measuring any speaker with current drive amp? Take the frequency response, then use voltage amp and match system response with DSP. Still better sound? As long as frequency responses differ it's hard to say what makes a difference. In theory the current drive, or reduced distortion, ought to give better sound, especially on small drivers in wide bandwidth application.
Replace with 'consistent'.
And yes, current drive suits the smaller units like compression drivers, as already mentioned by Cask05 (#22). Excursions are inherently very small, and there should be no variation in the Bl product. The sensitivity being high and the impedance being less peaky greatly simplifies amplifier voltage and current requirements, even when EQ is used.
Please note that the thing above regarding compression drivers was not meant to discourage you. The amplifier would be the least of your concerns, as you may have already guessed.
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