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In Reply to: Re: interesting posted by Henry Pasternack on April 13, 2004 at 16:11:56:
Henry wrote:::::(2) Symmetry is a pretty clearly defined concept. Either a circuit is symmetrical or it isn't.::::
Well, that certainly clarifies the concept with precision. In other words your saying it's 100% or nothing.
so that, if we have balanced output windings on a transformer... it's only balanced if it's 100% symmmetrical btwn the two halves from dc to light (frequency)... the cmrr would have to be, what? Infinity?
::::With balanced drive, the unadorned Compact's output stage is symmetrical. Without balanced drive, the question becomes how much imbalance we are willing to tolerate (as a consequence of finite tail resistance) before we say the thing is asymmetrical.:::::
Hello, Henry.... are you there.... no one has been talking about the "unadorned" compact (as published fifty years ago) as the archetype of high performance.... earth to Henry...
and... if we want to be more exact... who determines at what degree of imbalance a circuit is said to be "unbalanced"? Is this the best precision we can get?
are all interstage phase splitting transformers achieve perfect balance on the outputs? at what degree of error or what percentage of error do we then label it as "unbalanced"?
::::(3) With a constant current source in the tail, the amplifier should have reasonably good balance and performance. There are some second-order effects that will impact the balance, but theory and practice say the amplifier should perform acceptably this way.::::thank-you. so there MIGHT be hope for the patient. I sort of thought so myself...
::::In my opinion, this is a sufficiently evolved version of the circuit that it's no longer fair to call it the "Compact" (especially if you stick to the technology of the era and build the current source with tubes).::::henry.... how long ago were current sources and/or regulators used or developed? what about chokes? we could put a choke in the cathodes to increase the impedance as well.... chokes been around before 1961.... so does that keep the design authentic to the era?
your opinion as presented is laughable. so we shouldn't call any transformer made past the first or second decade of twentieth century a "transformer" since they evolved quite a bit over the next several decades in terms of design, materials, and winding practices...and a modern dry film teflon capacitor... since it is very different than the bathtub capacitors made in the twenties and thirties.... then the teflon ________ (blank) should not be called a "capacitor"....
and speakers of course to be true speakers would have to look like them cute projected trumpet speakers that pre-date the permament magnet type of drivers made several decades later.... so even an altec 802 cannot or should not be called a "speaker" or "driver" since it is an evolution of an earlier Lansing field coil type device.
nonsense....
::::(4) What you call "hypothesizing" is actually extrapolation from extensive practical experience. I have the confidence to say that theoretical predictions will closely match real-world performance as measured on the test bench. And I have some sense, within very broad limits, of what is likely to sound good, and what probably won't.:::::well, Henry.... if we're speaking of "confidences in our predictions" then perhaps I too could toot my horn just a little bit... but that gets into ungentlemenly public displays of self-affection...
but suffice it to say in this context.... that I had recommended to John Tucker the "compact" circuit initially and showed him where to get the schematic... and I showed this to John because the very first time I looked at it.... I realized that with the work that John has done in active loads, current regs, current sources, shunt regs and etc... I knew that John could bring this guy to life.... and I was right... John intuitively knew what was needed and saw also the beauty and elegance of the "compact" as an architecture and then set about building it and refining it.... to the point that one of the premiere recording studios in the US now has a pair in their studios....
::::(5) Poindexter's amplifier avoids the symmetry and performance problems of the "Compact" with the addition of one tube stage,::::nope.. has the exact same challenges... the circuit values will be different because they are different tubes and etc... but the level of refinement is no more or no less to make the phase splitter work at the front door than at the output stage....
:::which I would hardly call "much" more complex -- certainly not compared to the complexity of a constant current source.:::::
think outside your box, Henry. OK.... don't like a current source use a choke.... performs the same function in the sense of provides a high ac impedance....
what we need is a certain amount of impedance in the cathode circuit.... different devices will generate differing amounts of ac impedance.... one might use a resistor, a choke, or a current source... you pick the guy that best performs the function you need.
the rest is prostylsizing and religious dogma...
::::Thinking about the two solutions, we might want to reconsider our priorities. If the goal is true simplicity and all-tube design, then Poindexter's circuit comes out ahead.:::::
OK... Henry... we'll make the "ultra compact" all-tube... use another el-84 for your current source... siple enough....
again, you pick the right tool for the right job... and leave religion for your day off on sunday....
as much as I like Poindexter's.... it is more complex than the "compact" not less....
:::::If we can deal, conceptually, with lumping the constant current source into a black box, then maybe the modified "Compact" is more appealing.:::::Ok... this is a bit of what I have been aiming at in this discourse...
think of your "black box" as your "tool box".... we need to figure out which tools might work... a tube, a resistor, a ss current source, a choke, etc...
you keep on presenting one or two choices as though it exhausts the possibiity of outfitting our toolbox....
:::::I think we all agree that the basic "Compact" amplifier sucks.::::
well... how much imbalance does the stock compact have? what is our criteria on technical grounds for adjudicating a design as "sucks" because the phase inversion is not sufficiently good?
since you have never heard even the stock amp which you condemn then it must be on technical grounds that you have reached your "sucks" conclusion.... I'm just curious as to the obective criterion applied so that we might know when an amplifier does or does not suck...
::::The only way to make it work properly is to complicate it. And then it boils down to choosing between several more advanced circuit possibilities. There is no one right answer. Personally, if I'm going to bother with solid-state current sources, I'd rather go all the way and adopt Allen's solution.:::::go for it... it's an option available.... as is Lynn and Gary[s work... the compact is just another alternative...
and, again, you have blinders on.... you can only see in front of your nose.... how 'complex' is a choke for instance? what about a tube based current source? what.... throw gary Pimm's work out the window as to complex?
:::(6) This is not just semantic posturing. The technical issues are straightforward.;;;I believe I have addressed this contention already.
::::(5) With respect to Norman Crowhurst, frankly, many of his articles are less than lucid. I can do as good or better a job of explaining any of these subjects as Mr. Crowhurst, no offense intended to the memory of the dear old fellow. Obviously you feel my comments have been unclear or inaccurate, but reading your replies I don't find anything I want to revise, aside from my initial confusion (now resolved) due to your linking to the wrong schematic on Yeo's website.::::
first off... I did not link to the "wrong" schematic on Yeo's site.... the link provided was the starting point.... not hte ending point.... on the very same page whose url I posted were links to and an invitation to explore the 'refinements' that Yeo and Co. had experimented with.... so don't try to blame me that you could not have been bothered to read or simply peruse the whole page which I referenced....
regarding crowhurst... and your favorable alignment with the late crowhurst.... sorry, henry, as much as I like you... in terms of writing style and clarity your no crowhurst...
we haven't even gotten a good definition of "balanced" or "symmetry" yet... just some vague supreme court like enunciations like "I know pornography when I see it"....
:::If I've actually made any other mistakes, I will gladly correct them if someone will point them out to me. But, of course, just because someone says I'm mistaken, it doesn't mean I actually am.::::
good evening Henry.
-Mike
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Follow Ups
- Re: interesting - MQracing 18:04:41 04/13/04 (2)
- Re: interesting - Henry Pasternack 20:37:06 04/13/04 (1)
- Re: interesting - arend-jan 00:42:18 04/14/04 (0)
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