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Old 27th November 2012, 06:51 AM   #7671
dvv is offline dvv  Serbia
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Originally Posted by abraxalito View Post
Curious - which one did Dan design for B&W?
I honestly don't know. I got that info from an interview with Dan d'Agostino, in the section mentioning his external consultant design work, and was obviously surprised enough to remember that bit of info.

And I got the interview as reprinted material from Krell Industries which I contacted some years ago, and they appearently mistook me for a customer and sent me their tutta forza promo pack.

And I'm not a Krell freak, so I read it, and then threw it away.

So sorry.
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Old 27th November 2012, 07:06 AM   #7672
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Odd that B&W hasn't used his name then in their marketing materials (to my knowledge). After all it would be hard to come up with a better known name in beefy amps than his and I don't doubt his fee would be a substantial one... How long ago was this?
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Last edited by abraxalito; 27th November 2012 at 07:08 AM.
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Old 27th November 2012, 08:34 AM   #7673
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[QUOTE=dvv;3257928]Nige, you might try using a Burr-Brown 604 op amp, which is rated up to +/- 24V, if memory serves. Throw in a predriver, say MPSA 06/56, a driver pair, say MJE 15030/15031 and finish it with a pair of MJ 21193/21194.]

It was something like that . They can be arranged in Darlington or Complimentary feedback pairs . I seem to remember that at higher voltages the output stops at the +/- 18 V level with identical distortion . I suspect it has some built in regulation ?

This is all I can find of that project . Hope it is of some interest ? Note that the feedback cap can be shorted because the input is JFET , 14 mV offset is fine . The best capacitor is no capacitor . Try it with to be certain , sometimes against logic it is better . 10 uF is a bit small . The circuit was for my notes and not for showing to the world .

If anyone tries it you may want to enhance the output stability . Also an unregulated supply to the transistors and simple regulated supply to the op-amp .

The output cap was to be part of a crossover . 10 uF feedback cap OK if so .

BTW . From memory this version will already show very low distortion if reconnecting the feedback to OPA 604 output . Doubtless on simulations which I never do you will see a difference ? On my spectrum analyzer I didn't if memory is correct ? I set the base line at - 70 dB 2W . The bias was work in progress . I think 2 x 1N4007 and 5R4 almost was good enough to replace the Vbe ? It drifted a bit , not enough to matter ( 0.3 A ? ) ! I call this wrongly class AB 2 . The class B more like class G except no extra devices . The very low Vbe of the bias shows how close to acting like a single transistor a feedback pair is . An obvious way to do it , seldom seen .

The bass was driven by a Tripath class D amp ( not my choice ) . Using class A above 150 Hz is a nice touch and allows a simplified PSU . In my own system I would not use an output cap . For my friend it was a precaution , he had the choice . In the end we did it with KT 88 valves .


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Last edited by nigel pearson; 27th November 2012 at 08:57 AM.
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Old 27th November 2012, 09:15 AM   #7674
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Just going out now to try to fix my friend Renault heater !

Very likely some parts reversed labeled or the like in my dia . As said just my notes .

The 10 K Vbe current is low as it suited 2 x 1N4007 . Above that too much bias . I would try 4K7 or less if using this Vbe bias . This project progressed a bit from here , alas the notes are filed under some mysterious name I suspect . Good news is that this is a great launch point . Do try 2 x 1N4007 fixed directly to the outputs with epoxy . The resistor to set bias will be below 10 R from memory . The Vbe is mostly so as to have more current , measurements do not seem to indicate that it is required .
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Old 27th November 2012, 10:45 AM   #7675
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Odd that B&W hasn't used his name then in their marketing materials (to my knowledge). After all it would be hard to come up with a better known name in beefy amps than his and I don't doubt his fee would be a substantial one... How long ago was this?
I think that was one of the terms of trade. Aragon made no mention of it either.

I believe, but cannot prove, that it was d'Agostino who didn't want any mention made, lest some forelorn soul should deduce from it that Krell is not doing too well, so he has to moonshine work elsewhere.
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Old 27th November 2012, 10:53 AM   #7676
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....


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Well, I wouldn't do it quite like that. Darlington output sections have a nasty way of oscillating, and they are not as fast as emitter follower.

So, as I said, I'd use an MPSA trannie to drive an MJE1503x trannie, to drive whatever is at the output.

Also, I'd get the supply lines to run at say +/- 25...30V, and then use zeners to cut that down to say +/- 22V for the opa. That way, we have no effective voltage drop across the output stage (well, we do, but it doesn't matter), which would allow us to use the opa's full voltage output.

BTW, what the hell is that capacitor doing in the output line? Wouldn't it be better to use the usual trim pot to null the circuit's offset?
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Old 27th November 2012, 11:19 AM   #7677
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Well, well, ... this looks very promising indeed.

http://products.semelab-tt.com/pdf/b...20MG6331-R.pdf
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Old 27th November 2012, 01:35 PM   #7678
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Originally Posted by dvv View Post
Well, well, ... this looks very promising indeed.

http://products.semelab-tt.com/pdf/b...20MG6331-R.pdf
That does look interesting. The lumpy Ft curve looks like it could be based on real measurements too!

Comparable bandwidth to the old Sanken devices, better SOA I think. And based in merrie olde England
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Old 28th November 2012, 06:43 AM   #7679
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That does look interesting. The lumpy Ft curve looks like it could be based on real measurements too!

Comparable bandwidth to the old Sanken devices, better SOA I think. And based in merrie olde England
Agreed, Brad.

I compared them to MJL 3281/1302 curves and they look very similar, including the Ft curve.

Based on the graphs and specs, this trannie definitely has a lower output capacitance, which is almost identical to the new generation of Toshiba's transistors which replaced the old 2SC3281/2SA1302, the 2SC5200/2SA1943.

The fact that it is British was a surprise, even if a very pleasant one - I don't know what took them so long, but better now than never. Despite the fact that my personal views differ significantly from the British norms, so to speak, it was about damn time they rejoined the fray.

All I need to do now is to find out what do they cost, and then get my hands on a few samples, they seem too good to pass up.
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Old 28th November 2012, 10:01 AM   #7680
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Originally Posted by dvv View Post
Well, I wouldn't do it quite like that. Darlington output sections have a nasty way of oscillating, and they are not as fast as emitter follower.

So, as I said, I'd use an MPSA trannie to drive an MJE1503x trannie, to drive whatever is at the output.

Also, I'd get the supply lines to run at say +/- 25...30V, and then use zeners to cut that down to say +/- 22V for the opa. That way, we have no effective voltage drop across the output stage (well, we do, but it doesn't matter), which would allow us to use the opa's full voltage output.

BTW, what the hell is that capacitor doing in the output line? Wouldn't it be better to use the usual trim pot to null the circuit's offset?

As I said the output cap was to reassure my friend and was part of his crossover . As to output offset . No one has tested if it might be beneficial . I doubt if it is large enough to be so in typical examples . The idea being either to slightly reposition a voice coil or just to have slightly lower distortion . Having the cone very slightly held away from centre might do good ?

We make our houses too clean and help create immunity problems . Could low offsets being doing the same ? My instinct tells me it will do some good .

The stability is important . My conjecture is we can make the feedback pair become a super transistor . It has gain and linearity to rival any single device . We can even change Cob a little to make it even more obliging . The instability of this set up I believe to by mythical . I never saw it do anything one couldn't cope with . Millions of amps used it when Quasi Complimentary was popular . The extend it to an all complementary arrangement of 4 devices is no great leap . It also does make the two halves virtually identical and cheaply .

Also with Vbe bias it is possible to change this to boosted op amp use . I guess about 1.1 V required ?

If you calculate my use of power the critical question is how high to place the DC . I reckon +/ 18 V op amp and +/- 20 V outputs . As said the OPA 604 hits a brick wall at +/- 18 V from memory . The heat difference is not subtle when running even a low 1 amp standing current .

My research showed 4.5 W to be a critical class A requirement . I would hasten to say at 2 R is not daft . I would then say to convert to class G with 5 Watts A and 100 W G is perfect .

BTW . Like those transistors .
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