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Old 29th June 2012, 11:12 AM   #6511
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Hi F like football it isn't a matter of life and death , it's far more important than that ( a football quote of who I don't remember ) . Football is an example , glad to say I didn't watch one game ( I pretended I did ) .

Dvv , what's Dubrovnik like ( and food ) ?
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Old 29th June 2012, 11:29 AM   #6512
dvv is offline dvv  Serbia
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Quote:
Originally Posted by nigel pearson View Post
Hi F like football it isn't a matter of life and death , it's far more important than that ( a football quote of who I don't remember ) . Football is an example , glad to say I didn't watch one game ( I pretended I did ) .

Dvv , what's Dubrovnik like ( and food ) ?
Dubrovnik is also called the Pearl of the Adriatic. Beautiful, unjustifiebly expensive, short of great beaches, but surround by extremely clear water. Also, good street music groups. Some very good hotels.

All in all, not a bad deal at all.
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Old 29th June 2012, 02:20 PM   #6513
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DVV

On the series pass regulators to the driver sections be sure to put a reverse diode across the pass transistors. If the output section capacitors discharge first there will be reverse voltage across them!

ES
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Old 29th June 2012, 04:04 PM   #6514
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Quote:
Originally Posted by simon7000 View Post
DVV

On the series pass regulators to the driver sections be sure to put a reverse diode across the pass transistors. If the output section capacitors discharge first there will be reverse voltage across them!
Only if something before pass transistors are bleeding such current that can damage them.
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Old 29th June 2012, 04:24 PM   #6515
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Quote:
Originally Posted by nigel pearson View Post
I used to spend a lot of time reading the archived Wireless World magazines at what is now Oxford Brooks University .

The test they did although primitive was interesting . A small wire touching a metal strip on a bass unit . They found a damping factor of 3 to work as a minimum . This was I think 1955 . The suspension of the speaker I suspect would have been much stiffer than now . The testing was done with a full understanding of the problem and not by some armature .

When the British Hi Fi press looked at this many years ago I seem to remember 16 was held to be where cables mattered more . The use of a series resistor on a normal amp ( damping factor > 100 ) will tell you much of what you want to know . Sid Smith of Marantz though some of the sound of tube amps was down to that alone . Some say it helps the negative feedback work better in the amp . Seems very likely it would . I think a resistor preferable to the usual choke if the amp allows . Big resistor small choke perhaps ideal ? 1 ohms seems OK to me . For choke 5 turns 1 mm x 10 mm air cored . Try earthing your speaker metal work also . It costs you nothing to try . Perhaps 2 x 1K non inductive to RF " hum-buck" it ( speaker +/- to ground , or caps ) ?

Slightly under damped is usually nice . Especially if the speakers are correctly damped ( what your computer said was correct ) . 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 ?

BTW , please don't tell me WW were wrong . They weren't as at least they were trying to test the reality of the concept .
A very useful information.

Thanks a lot, Nigel !
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Old 29th June 2012, 06:27 PM   #6516
dvv is offline dvv  Serbia
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Quote:
Originally Posted by simon7000 View Post
DVV

On the series pass regulators to the driver sections be sure to put a reverse diode across the pass transistors. If the output section capacitors discharge first there will be reverse voltage across them!

ES
Thank you for the heads up, rest assured that I've been putting reverse diodes for like 20 years, ever since I fried to a crisp one such regulator because I was "saving" on the parts.

These days, my regulators are all discrete, and hence more complex and more expensive, so caution is necessary all the more so.
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Old 29th June 2012, 06:37 PM   #6517
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Originally Posted by Wavebourn View Post
Only if something before pass transistors are bleeding such current that can damage them.
Anyway, Wave. In the total cost of it, a few diodes are meaningless. Anyway, a 1N4004 diode costs like a little more than nothing.

Besides, I am an out and out freak for safety. You've seen the not insignificant effort, money and PCB real estate I normally dedicate to all sorts of protection circuits. And you haven't seen all of it yet.

You would be too if you just saw all the EU electrical safety regulations I must satisfy to be able to sell in the EU. That is literally thousands of pages of text, mostly legalese, but some of it actually technical.

And then thers's the question of conscience. It it should ever happen, God forbid, that any one of my customers should get shocked, never mind the law, I would never forgive myself. That makes you think the darkest shade of black, because there is no end to human stupidity.
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Old 29th June 2012, 06:44 PM   #6518
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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 ?
The design was supposed to be 'adequate'. BBC's words.

Last edited by Pano; 29th June 2012 at 07:30 PM. Reason: fixed quote
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Old 29th June 2012, 06:45 PM   #6519
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Very very true, in the end it's all about doing what we do safely. Don't take any shortcuts, ever.... Now back on topic
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Old 29th June 2012, 06:52 PM   #6520
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In loudspeaker test specifications damping factor was only added in the latest revision. I think now, the driving equipment must have a source impedance of 5% of the loudspeaker's rated impedance.

The result is that many loudspeakers have been designed with test setups much above this. The prior idea was that you measure the voltage at the loudspeakers terminals and keep the voltage constant so the results should be good.

The change went through as fast as it could be typed out!

So if you are looking to the future more manufacturers will be voicing their systems with real damping factor of 20 or higher.

Of course for backward compatibility you can place a very small inductor/resistor combination in series with your loudspeaker line.
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