Frank, the split supply logic is with me since 1978, when I made the first model of that German LAS amp, mentioned here some time ago (with schematic).
In some ways, it was years ahead of its time.
Electronically regulated VAS power supply lines make the imaging rock stead no matter at which volume level you push it. It helps with imaging, although it in itself doesn't make any amp great, meaing that it's still you as the designer who has to make it image well in the first place.
The other great benefit to my mind is that it allows you to actually lower the supply lines for the output stage because the inevitable losses of the VAS are taken care of. But your output stage works at lower voltages and is thus more within the SOAR curve of the output devices. However, if you do lower them, make sure you have some stiff power supplies.
As an example, my 100W amp uses +/-58V regulated for the VAS and +/- 51V for the power stages. Under low power demands, the power stage voltages will rise by 3% or so (I use custom made toroids).
In some ways, it was years ahead of its time.
Electronically regulated VAS power supply lines make the imaging rock stead no matter at which volume level you push it. It helps with imaging, although it in itself doesn't make any amp great, meaing that it's still you as the designer who has to make it image well in the first place.
The other great benefit to my mind is that it allows you to actually lower the supply lines for the output stage because the inevitable losses of the VAS are taken care of. But your output stage works at lower voltages and is thus more within the SOAR curve of the output devices. However, if you do lower them, make sure you have some stiff power supplies.
As an example, my 100W amp uses +/-58V regulated for the VAS and +/- 51V for the power stages. Under low power demands, the power stage voltages will rise by 3% or so (I use custom made toroids).
Many years ago I was having an argument with my boss . He had trained for many years as an engineer and could speak 21 languages , 7 fluently . This last fact gained the JET project for the UK as he worked as a translator with engineering background . My argument was we often could make better things using our ears with measuring backup . He was always dubious . I think he realized I made better designs than he . His one statement was that tyres supported my argument . Every tyre company had an expert who knew mostly what the expert in the rival company knew . That didn't stop the gifted expert from better understanding the requirements . His master statement was the science then guarantees the exact reproduction of the design in every tyre made . He insisted that only a fool would see wrong in that .
I often felt he he knew too much and understood too little . However he very accurately defined how science ideally works . His famous question to me was " does it have the discerning capability " . That was his tongue in cheek way of giving the discerning to the amplifier rather than us . It was a good way to say it . Does the amplifier or whatever allow us to hear with ease ?
I often felt he he knew too much and understood too little . However he very accurately defined how science ideally works . His famous question to me was " does it have the discerning capability " . That was his tongue in cheek way of giving the discerning to the amplifier rather than us . It was a good way to say it . Does the amplifier or whatever allow us to hear with ease ?
As a side note, consider what I will call the Glenn Gould factor. Someone is playing a real piano at the far end of your home, you're at the other end. You can hear the piano is 'real', and is being played with consummate skill. You then start to walk towards the piano, walk into the room where it is, and sit down next to the the pianist - all the time the pianist continues to perform. You lean towards him, you can hear every breath he takes, the squeaking of the peddle, the rubbing of parts of his clothing on the stool, the clacking of the edges of his finger nails ...
While you hear these things, is the piano sound an irritating, overloud, overwhelming, distorted mess? Why not, at this moment it's hugely loud, dynamic, compared to those subtle sounds you're hearing of the mechanical aspects of the person playing? Well, if not, perhaps it's because the ear/brain has a remarkable ability to separate sounds when each is "correct", not overlaid with meaningless, unconnected noise/distortion ...
For me, that's what an audio system needs to do, to create the convincing illusion, to sound "real" ... something a high percentage of them fail to do ...
While you hear these things, is the piano sound an irritating, overloud, overwhelming, distorted mess? Why not, at this moment it's hugely loud, dynamic, compared to those subtle sounds you're hearing of the mechanical aspects of the person playing? Well, if not, perhaps it's because the ear/brain has a remarkable ability to separate sounds when each is "correct", not overlaid with meaningless, unconnected noise/distortion ...
For me, that's what an audio system needs to do, to create the convincing illusion, to sound "real" ... something a high percentage of them fail to do ...
But in the situation you describe you also have the ability to move around the sound sources, hearing subtle cues due to their relative locations, with your outer ears contributing other directional filtering effects, and so on. I think we're deluding ourselves if we think we can achieve anything like this from a recording made with two fixed microphones (or worse an arbitrary multi-mic mix) and reproduced from just two speakers, except in very special, limited circumstances (girl and guitar maybe!). Audio holography is a wonderful idea, but it's not going to come from two ordinary speakers and ordinary recordings. The pursuit of this Invisible Speaker trick seems like a blind alley to me. It's another example of the common audiophile myth that somewhere out there is a perfection where everything falls into place and the Invisible Speaker emerges, if only they can remove all the distortions through ultimate minimalism.
Not perfection, but sufficient to create an effect which is very satisfying: it's pretty obvious that a number of people have got there via a number of techniques, which all essentially involve getting a complete system in a sweet spot of behaviour. I guess if one has never experienced such, it could be quite frustrating hearing it being discussed as a 'gold at the end of the rainbow' thing, but that shouldn't stop it continuing as an achievable goal.
For me, getting better sound and the invisible speaker go together; I can get to a certain point of quality or "transparency", and the sense that the speakers could disappear becomes stronger. Overall, the benefits of getting a system to a high degree of tune are just too great, to chuck the idea in the bin because it all seems too hard ...
A question . Douglas Self says mostly something described one way will always show up in simple harmonic and IM distortion traits . Settling time ?
Bob Stewart said realistically hi fi stops at one voice and one guitar . I do notice when most convinced it is always vinyl or live FM . Quad ESL 63's ice the cake . My friend had a pair with no covers . His daughter of 5 was always near them ! Eyes closed and they do disappear . strangely even 78's seem to work . The brain quickly synthesizes the lost malformation it the timing correct .
I listened to some old video called Jazz 625 ( BBC 2 1964 ) . My eyes tell me the very best mics used . The sound a total disaster . Most 78's would be far better . Somewhere along the line someone didn't finish the job . I don't buy the idea of TV sound . That should be done in the transmission studio . This is the best example of close the eyes and have no illusion , it is rubbish . So sad as history flushed down the pan .
Bob Stewart said realistically hi fi stops at one voice and one guitar . I do notice when most convinced it is always vinyl or live FM . Quad ESL 63's ice the cake . My friend had a pair with no covers . His daughter of 5 was always near them ! Eyes closed and they do disappear . strangely even 78's seem to work . The brain quickly synthesizes the lost malformation it the timing correct .
I listened to some old video called Jazz 625 ( BBC 2 1964 ) . My eyes tell me the very best mics used . The sound a total disaster . Most 78's would be far better . Somewhere along the line someone didn't finish the job . I don't buy the idea of TV sound . That should be done in the transmission studio . This is the best example of close the eyes and have no illusion , it is rubbish . So sad as history flushed down the pan .
I have the other belief ... enough times I have heard "impossible" recordings come together to create an enjoyable listening experience, to say, "never say never". Even when severely mangled, it seems that enough sound information has been preserved so that if it's handled well enough by a very high quality playback mechanism, then the ear/brain can compensate for all the inadequacies, and the musical event still retains its integrity.
I've also heard people swear that they had achieved a gambling system that worked, had premonitions that turned out to be true, achieved out-of-body experiences, seen ghosts. Strangely, I don't find it frustrating that I have never (convinced myself that I have) experienced them too.
I am, in fact, being very positive about non-holographic audio. I find the sound of two conventional but active, time-aligned speakers that aren't pretending to produce the Invisible Speaker trick, glorious. That's all I expect of them because that's all stereo is really designed to do. They sound fabulous from the nominal listening position, and they don't sound ridiculous from anywhere in the room.
No pretending involved, it just happens! It sounds like they're in an excellent shape already, it's just another step they could go to, with a touch more refinement in some area of the playback chain.
As mentioned elsewhere, the clues of where attention would be rewarded is careful listening to your "worst" recording. Why, in what way is it bad ? ... Consider that it may be telling you, giving you clues as to where the remaining weaknesses are in the system ...
I didn't imply "pretending", merely delusion.
A while ago I thought I had discovered the secret to a kind of audio perfection when I first went beyond using text book crossover filters, and tried phase-correcting some two way active speakers. What I heard was possibly something like your Invisible Speakers: on orchestral music the sound stage seemed to spread far beyond the speakers, and there was the most wonderful holographic 'ambience' and I fancied I could hear the timpani at the back and strings in the front etc. The narrative I came up with was that I had never heard truly correct speakers before, and that this must be what it was like when everything lined up. I think I even wrote a post announcing my enlightenment. It was only later that I noticed that recordings that should sound 'dry' were also exhibiting a subtle ambience that hadn't been there before. At first I thought it was that the processing had corrected genuine components that had previously been cancelled out, but I eventually discovered that my code was completely wrong, and far from correcting the phase I was adding arbitrary delay effects.
Technically wrong, but this had not stopped me from believing that I had finally discovered a kind of holographic perfection. It was only because I listen very critically to a wide range of music that I noticed my error. In my case it was my religious belief that maybe there was a path to audio perfection through DSP, but for others it is through the elimination of components in the signal path, or reducing distortion, noise and interference by changing cables or taking the backs off their speakers. (No measurements to point to as evidence, of course; merely anecdote.) A narrative can be spun for any and all of these things, but they must be taken with a pinch of salt, in my opinion.
That is what I thought. There may be a 'large signal' contribution at first for a large step input, but that will quickly fade away unless the circuit is sticking to a supply rail (for example). What is left is small signal. Fast settling means wide (closed-loop) bandwidth and no ringing caused by peaks just above the passband i.e. well-behaved HF phase response.Barleywater said:
This is an old but pretty good review: http://www.analog.com/library/analogDialogue/bestof/pdf/04_1.pdf
Where did he say that? I'd like to read it.
I'd also still like to know how he managed to wind up with so much noise. As well, based on JA's experience, the very pretty heatsinks are evidently inadequate for the JA traditional preconditioning regimen. It is a beautiful industrial design though, and I'm sure under normal circumstances the thing won't overheat.
Before he left Teledyne Philbrick, Pease wrote a couple of pieces on settling time and in particular settling time measurement. The historical context was a fierce rivalry between TP and ADI, and I suppose perhaps Burr Brown as well, which was probably stoked by the Demrow AD article --- Wurcer probably knows the details. I have the Pease material somewhere buried in old files, but I recall he had a circuit for a very fast bounded amplifier for measurement of the settling point (see the Demrow article). And as well there was a circuit for cleaning up the generator signals. Even better, I recall he shows a technique with floating power supplies for measuring the settling time of a voltage follower, remarking that it actually does work
I designed, built, and used a lot of custom fixtures circa 1975 when I was concerned about this stuff and could only spend small amounts of money per day without getting approvals and going through UCLA Purchasing. Good thing management was indulgent, or at least barely knew what I was doing!
Note that the focus on settling time in opamps was/is for data acquisition and not audio. Exactly how the amp settled --- the shape of the slewing and overshoot etc. waveform, its symmetry or lack of it --- was of very much less importance than knowing that after a sufficient delay, you could sample and hold (or stop tracking and hold) and convert. A controversial issue is how much of the generally-ignored behavior in the slewing-settling interval might be audible. As far as I know this has not been rigorously tested.
I doubt that it is a huge effect compared to things like momentary hard overloads with highly asymmetrical program material, but it's a potential area for investigation. At some point, despite the usual grumbling that amplifier effects are negligible compared to loudspeaker aberrations yada yada, someone like Olive ought to get round to it.
Of course sensible bandlimiting ahead of the amplifier is one strategy, but some insist this is deleterious.
CopperTop:
Pre-echo and post-echo artifacts are stock and trade issues that must be dealt with using appropriate smoothing windows both on IR measurement and on candidate inverse filter. Easy check is close inspection of tails resulting from convolution of inverse filter with measurement IR.
Brad, thats where we separate the hobby and intellectual pursuit of higher and higher objective performance, from the real need for such performance. I strive for performance in my source and amp builds that is likely far more than needed, but I recognize, for me, that the hobby part needs to be intellectually rewarding of the time sunk into it, in addition to the pleasure of listening to and playing at producing music.
I think high slewrate and bandwidth is useful to a point, but I do bandlimit the audio input. with so much RFI and EMI spilling all over the place, massive slewrate and bandwidth for the sake of it, starts to become a hindrance and all round PITA
I think high slewrate and bandwidth is useful to a point, but I do bandlimit the audio input. with so much RFI and EMI spilling all over the place, massive slewrate and bandwidth for the sake of it, starts to become a hindrance and all round PITA
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