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Old 29th June 2012, 07:12 PM   #6521
dvv is offline dvv  Serbia
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Quote:
Originally Posted by nigel pearson View Post
The BBC used to say LS3/5A was critically under damped . Some who think the LS3/5A to be the world most accurate speaker might be surprised by that ?
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Originally Posted by spladski View Post
The design was supposed to be 'adequate'. BBC's words.
And "adequate" says it all perfectly.

People like to forget that the LS3/5A was initially developed for ENG purposes, so it had to fit in a report van, where space is at an ultra premium. When taken that way, it was a rather good solution.

Taken as a home speaker, it was a joke.

Last edited by Pano; 29th June 2012 at 07:32 PM. Reason: fixed quote
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Old 29th June 2012, 07:23 PM   #6522
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Originally Posted by dvv View Post
Anyway, Wave. In the total cost of it, a few diodes are meaningless. Anyway, a 1N4004 diode costs like a little more than nothing.
If you mean sudden shorting of filter caps by a screwdriver 1N4007 may not survive. Base-collector junction of pass regulator can be more robust than it.
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Old 29th June 2012, 07:33 PM   #6523
Pano is offline Pano  United States
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Please use the quote function correctly. Misuse leads to misquoting, which is against the rules. Thanks.
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Old 29th June 2012, 07:41 PM   #6524
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Originally Posted by simon7000 View Post
In loudspeaker test specifications damping factor was only added in the latest revision.
Whose's specifications? I would like to know. This whole arena has been so devoid of reference standards its silly. Even the FTC is not very aware of its own rules.

Designing speakers to agreed upon standards would be great. The only thing close is THX, who tries to keep their standards a secret.
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Old 29th June 2012, 07:48 PM   #6525
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Originally Posted by 1audio View Post
Whose's specifications? I would like to know. This whole arena has been so devoid of reference standards its silly. Even the FTC is not very aware of its own rules.

Designing speakers to agreed upon standards would be great. The only thing close is THX, who tries to keep their standards a secret.
AES has a standard for loudspeakers, drivers not systems. The method is often applied to entire systems and is being expanded to cover them.

see SC-04-03 meeting report, Budapest, 2012-04
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Old 29th June 2012, 07:54 PM   #6526
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Originally Posted by Wavebourn View Post
If you mean sudden shorting of filter caps by a screwdriver 1N4007 may not survive. Base-collector junction of pass regulator can be more robust than it.
Wavey,

The main capacitor bank will be 10,000 uf or more. That powers the output stage. The driver section is fed from a regulator.

There is a different supply for the driver stages. If the primary capacitor of the regulator circuit drops before any capacitors on the output discharge, then the regulator transistor is going to breakdown above 6-9 volts of reverse voltage.

If the regulator section input capacitor discharges before the output stage, under some conditions this can place a reverse voltage on the outputs and drivers, very bad news. But that is unlikely to happen.

If you short the main capacitor bank it will not cause any load on the reverse protection diode.

Now I know why those glass case transistors you use glow so red!

ES
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Old 30th June 2012, 06:41 AM   #6527
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Originally Posted by Wavebourn View Post
If you mean sudden shorting of filter caps by a screwdriver 1N4007 may not survive. Base-collector junction of pass regulator can be more robust than it.
That, and throwing a stick of TNT into the device, with a lit short fuse.

Come on, Wave, how many users are likely to do that? We're talking about standard ops, not about acts of terrorism and/or vandalism.

But, since I generally use just three types of diodes (1N4148, 1N400x and 1N5406), I guess I could use the 1N5406 instead.
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Old 30th June 2012, 07:00 AM   #6528
dvv is offline dvv  Serbia
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Originally Posted by 1audio View Post
Whose's specifications? I would like to know. This whole arena has been so devoid of reference standards its silly. Even the FTC is not very aware of its own rules.

Designing speakers to agreed upon standards would be great. The only thing close is THX, who tries to keep their standards a secret.
Hear, hear!

That's what I have been lamenting for two decades now. In the 80ies, there was a move away from practically all standards or attempts at standards. Some standards, like DIN 45500, were hopelessly behind the times as the German industry moved from manufacturnig to buying in, and as it was run over by the Japanese and the Americans (who also purchased their share of German quality companies), leaving only small, specialist companies to go on. IHF standards were never really adopted in Europe in general, which is a pity, because even poor standards are still way better than no standards.

The first en masse standards renegades were the Brits. Look over their ad material form the period and you will see about as many ways to declare power output as there are manufcaturers. Try </titlehifi> <link rel="shortcut icon" type="image/x-icon" href="http://wegavision.pytalhost.com/favicon.ico"> <title>HiFi Archiv

Then the Scandinavians joined in, and the Chinese were the last to join the fray. In their earnestness to make and sell, sell, sell, I find that in many instances they simply threw the standards out of the window, their sole concern being that it's cheap and that it looks more expensive than it really is - some call it "bling".

And very soon, this becomes dangerous. On a different forum (duyaudio.sr), there's a discussion about Chinese made Schuko sockets, which are dirt cheap, but some were found to melt after a while - and that's 230 VAC/50 Hz they are supplying, perfect for a nice home fire. You can use your smouldering house to bake some marshmellows.

However, as I said there, this could not be possible if our goverment authorities did their job. Random testing, find something to be below current official standards, and simply ban it. Of course, that means actually working for their pay, and it might pi*s off the Chinese, and no VAT and/or local taxes, so nobody seems to give a damn.
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Old 30th June 2012, 09:32 AM   #6529
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Originally Posted by spladski View Post
The design was supposed to be 'adequate'. BBC's words.
As a Brit ( well Brit flag , sorry to assume , living here anyway ) you should understand understatement , the BBC are masters of it . The reference to " perfect " was about devotees and not the BBC . I knew Robin Marshal who I suspect understated his part in it ( Audio Master ) . I think I could call Spencer Hugues a friend ( Spendor ) .

The one thing people never get excited about in LS3/5A is the auto-transformer to the tweeter . I was baffled by it ( no pun ) . Big money and added distortion . Even though I do not know the exact reason it was done I take it to be the better way . My speculation is that it allows better control of the tweeter by the amplifier ( yes and level ) . If that is true an op amp like 5534 ( or better ) as a buffer might drive a tweeter ( 60 mA in close to class A ) . It could be fed from the main amp if better was not available . Now that's something to do when it rains ( always Dvv where I live ) . Remember 5534 is not happy at unity gain so measure first on scope . Sorry everybody I have about 50 x 5534 which get used first . Something posh later . MC 33079 , that's 80 mA if used in paralell . They are happier at unity gain . We could use the inverting input as driving a low impedance is not a problem for a power amp . Also the current limiting action might protect the tweeter ? In the unlikely event there is not enough voltage drive use in bridge ."Something better " would be a matched branch form the preamp . This would automatically match the power amp . This would use the positive input and could be configured as a filter also .

The critical under damping is also applicable to amplifiers . Impedance matching between stages matters greatly , be brave and try what is said to be wrong . If it is you will soon know . As the amplifier almost invariably has a global feedback loop it is sometimes difficult to know what has been acheived by any modification . The ears are surprisingly good at helping here ! Sorry to put it that way . Seems to me too many amplifiers are designed by the great ears of Mr L T Spice . I never met the man so must be careful not to assume his ears to be inferior to mine .

All joking aside . Damping is very important . Trans-conductance an ideal for power stations more than hi fi .

Last edited by nigel pearson; 30th June 2012 at 09:35 AM.
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Old 30th June 2012, 11:42 AM   #6530
dvv is offline dvv  Serbia
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Nige, in the end, the sound of any audio product is determined by the hearing of its creator(s). Getting a circuit to work proprely in purely electrical terms is not too hard, but making it sound RIGHT is a whole new ball game.

I'm fairly certain that you have met up with products which measure out of this world, yet sound dull, boring or even wrong. And others which don't measure too well at all, yet somehow sound divine.

This is, in my view, the greatest problem with industrial fare, the fact that there's a team of engineers, each with a different hearing, voicing the product, which ends up as a compromise acceptable to most of them, if not all.

Whereas you and I are much luckier in that respect, because we have only our own hearing to satisfy. If it sounds right to you, what do you care what other people may think, if you're doing it just for you (i.e. non-commercially)?
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