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Old 4th December 2012, 07:19 AM   #7751
dvv is offline dvv  Serbia
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Oops! Was it something I said?
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Old 4th December 2012, 09:21 AM   #7752
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No , I think you and I are always in the crows nest .

I caught the tail end of discussion about DNA today whilst shaving . I suspect the gentleman talking would rank higher than any of us even allowing for different disciplines etc . He made an interesting statement . He was the one who discovered that a Chimpanzee is 95% the same DNA as us . He had thought 60% as a guess ( how many here would admit to guessing ) . He then went on to say having been asked why people differ between lets say Africa and the so called West he said it can not be in the DNA as that is more or less identical . Thus it must be food and encountering different animals plus farming that makes us different . My instinct is to say if we get everything that describes us from 5% of our DNA then how small does small need to be? My bet is Einstein wasn't so different in DNA ? Hi fi I know for a fact is very small differences with large outcomes . It is very complicated . I do accept that sometimes making a circuit more complex actually reduces the problems . That is the focus .

I think in 1971 Peter Blomley sent a letter to Wireless world about a novel approach to amplifier design . Alas I can not find a reference to it worth showing ( Perhaps D Self ) . From memory it split the amplifier earlier than usual to create more stable class B operation . I think it said the two halves working independently ? The signal was feed if I am correct into a double common base stage fed by two current sources ( current mirrors ) . I think it's virtue was it could not be set up incorrectly as long as set to the standard recipe . Again from memory Mullard used the circuit for their budget priced modules , Even future in my memory that he worked for them ? Anyone ever tried it ?
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Old 4th December 2012, 01:18 PM   #7753
dvv is offline dvv  Serbia
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I make a lot of guessess. Not my fault that a fair number of them turns out to pretty correct.

But guessing is invariably linked to personal experience. For example, I'm willing to bet that John's guess would be much more accurate than mine and most of us here simply because he's been at it much longer and much deeper than most of us. He's seen more than most of us, tried more also, all of which served to build his experience to a point where his guess will most often turn out to be right, or very near right.

I think that's quite normal and only to be expected. I have the same thing with my good wife - she's been teaching medicine and doing basic research in her lab for 33 years, she's practically breathing her field (pharmacology). So if you ask her why do you react to a drug in a certain way, chances are 99% that she will give you the right answer, after she asks a few questions. And she may well astound you with a claim or two, which may appear to be totally crazy, but listen to her, try it out and it won't be crazy at all. After 28 years of marriage, I have long stopped wondering or being amazed.

As for DNA, much as we have learnt about it, we are still just scratching the surface. But at least we're on our way.

What you said about the unnamed gentleman, sound awfully like a balanced topology, where you have two standalone amps working in parallel, after a common input stage, usually a dual FET. One side drives the plus side of the load, the other the minus side.

If that's it, then I can send you some Sansui schematics, they were big on it with their Double Diamond DC topology.

Sony's approach is rather interesting. In one of their models from high up on their range list (I forgot the model number, but I should have its Service Diagram, so if anyone wants a peek, just let know), they start out just like a common, regualr amp regarding the voltage gain stage, but then switch to fully balanced for the current gain stage, qwith lots and lots of power transistors.

Not knocking it, but so far, I am quite happy with a classic fully complementary layout. thank you.
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Old 4th December 2012, 01:54 PM   #7754
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This looks a little bit like the Blomley design . I think it was A new approach to class B amplifiers Wireless World 1971 Peter Blomley ?

http://www-f9.ijs.si/~margan/Articles/Class_B_Dist.pdf
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Old 4th December 2012, 07:51 PM   #7755
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looked at the link a.wayne posted earlier with Steven Guttenberg and the two other guys (sorry, not a names person).
I frankly believe now that Steve has no clue. he brings absolutely nothing new to the discussion and simply keeps repeating flawed arguments. why they needed to have an 1 hour long talk to reach the surprising conclusion that a FR plot doesn't tell everything, beats me...
well, based on that I conjecture that 500 years from now they'll have similar discussions about why certain brain implants sound better.
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Old 5th December 2012, 06:48 AM   #7756
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Sometimes, it takes a long discussion to arrive at well known conclusion.

Here, for example, we had a discussion on why should we use FETs for our input stages. It took like 20 pages for someone to put forth the somewhat obvious argument that two BJTs in differential mode, when given enough bias current and when their gain has been degenerated by emitter resistors to something below 10:1 actually starts to act more like a FET than your typical BJT.

While still not quite the same thing, it's getting awful near to it. And no voltage issues, either.

But it was still fun.
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Old 5th December 2012, 09:05 AM   #7757
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Hi Mr Push Pull . It took myself and Dvv weeks to assert that maybe medium speed output transistors sound better . That is a radical concept as it sits between the only thing wrong with 2N3055 is it's lack of voltage and go as fast as you like it never will be fast enough . I countered that by saying perhaps we should use complimentary feedback pairs ( CmfbP ) of virtually anything you please but slug them a little bit to mimic the conditions of the slower device .

Douglas Self says the EF output has the advantage if done correctly to empty the output devices of minority carrier charges . MOSFET's do not have them so the problem goes away . I fancy that the Blomley amplifier can better use the CmfbP ?

There is a very primitive kit sold by Velleman . The output devices ( TIP 142 /7 perhaps ) are slugged with a capacitor each . One critic said obviously a bad design to need that . We don't say that of the VAS cap usually do we ? In fact Self says get Cob as low as you can and make the VAS cap as high quality as you can . As he says the external cap is bound to be better than what a BD139 gives you gratis . Some say that single input transistor stages are more stable . Can't say I noticed that given a low Cob VAS .

Einsteins brain was 1.2 Kg , most are 1.4 . There is a daft body to brain mass ratio to express something ? Glad in Audio we are not that badly unknowing .

I see DVV and me as two salty old sea dogs out in all weathers keeping this ship going . OK we will never be Captain , our scares and weathered faces say we might be experts in the trade of the sea . Sometimes it gets like the Tale of the ancient mariner , is the Albatross class D , or what I call cake mix amplifiers ( you buy a packet and say you baked a cake ) ? Dvv I hope you did that poem when in Somerset ?
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Old 5th December 2012, 01:19 PM   #7758
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Which poem? I did a lot of poems in those days, English Lit was choking on them, both on O and A levels.

I still fondly keep my Jackdaw collection of folders.

And of course, the cider was a heavenly nectar!
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Old 5th December 2012, 01:57 PM   #7759
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Quote:
Originally Posted by nigel pearson View Post
Hi Mr Push Pull . It took myself and Dvv weeks to assert that maybe medium speed output transistors sound better . That is a radical concept as it sits between the only thing wrong with 2N3055 is it's lack of voltage and go as fast as you like it never will be fast enough . I countered that by saying perhaps we should use complimentary feedback pairs ( CmfbP ) of virtually anything you please but slug them a little bit to mimic the conditions of the slower device .

Douglas Self says the EF output has the advantage if done correctly to empty the output devices of minority carrier charges . MOSFET's do not have them so the problem goes away . I fancy that the Blomley amplifier can better use the CmfbP ?

There is a very primitive kit sold by Velleman . The output devices ( TIP 142 /7 perhaps ) are slugged with a capacitor each . One critic said obviously a bad design to need that . We don't say that of the VAS cap usually do we ? In fact Self says get Cob as low as you can and make the VAS cap as high quality as you can . As he says the external cap is bound to be better than what a BD139 gives you gratis . Some say that single input transistor stages are more stable . Can't say I noticed that given a low Cob VAS .

Einsteins brain was 1.2 Kg , most are 1.4 . There is a daft body to brain mass ratio to express something ? Glad in Audio we are not that badly unknowing .

I see DVV and me as two salty old sea dogs out in all weathers keeping this ship going . OK we will never be Captain , our scares and weathered faces say we might be experts in the trade of the sea . Sometimes it gets like the Tale of the ancient mariner , is the Albatross class D , or what I call cake mix amplifiers ( you buy a packet and say you baked a cake ) ? Dvv I hope you did that poem when in Somerset ?
DVV is salty .......
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Old 5th December 2012, 02:05 PM   #7760
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Quote:
Originally Posted by nigel pearson View Post
Hi Mr Push Pull . It took myself and Dvv weeks to assert that maybe medium speed output transistors sound better . That is a radical concept as it sits between the only thing wrong with 2N3055 is it's lack of voltage and go as fast as you like it never will be fast enough .
2N3055... you reminded me of a board collecting dust (clearly visible) in a drawer. I made it in high school, some 17 years ago. the only thing preventing me from binning it are its neat looks, my PCB etching and soldering skills seem to have been superior at 16.
please ignore the two compensation diodes that are obviously supposed to be physically bonded to the output transistors (I only said my soldering skills were good). and the 8-pin device is the poor old 741. based on a 70's Uher amp schematic.
oh and the long cap leads are because original parts were large axial types.
Click the image to open in full size.
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Last edited by mr_push_pull; 5th December 2012 at 02:09 PM.
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