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Old 25th June 2012, 02:11 PM   #511
Waly is offline Waly  United Kingdom
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Quote:
Originally Posted by Edmond Stuart View Post
Anyhow, I refuse to design 'Wilson WATT friendly' amps.
Your call to do so. What would then be the maximum load current target for designing a 4 ohm friendly amp, say of 200W nominal (into 4ohm resistive)?

The whole topic was raised by the claim about the capacity of three pairs of lateral mosfets driving 4 ohm speaker loads (and not necessary Wilson PUPPY), with +/-60V rails, while keeping the distortions near clipping anywhere close to acceptable.
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Old 25th June 2012, 03:35 PM   #512
wahab is offline wahab  Algeria
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Originally Posted by Edmond Stuart View Post
Hi Wahab,

>high output Z amplifiers
That's another story.
I mean, if the LS impedance is flat and resistive, instead of 100A, just 10A will do.
Wouldn't that be far more economical?

Cheers,
E.
Hi Edmond

The problem surely arise with 4R speakers , but i doubt that 8R siblings
could manifest such low impedances as 2R at some frequencies unless
the design is badly misguided , be it electricaly or acousticaly.

This is unfortunately a general trend that speakers manufacturers
dont bother about providing stable loads to the amplifiers.

Perhaps that impedance curves should be provided along
with frequency responses curves , as it would allow the consumer
to choose more accurately a given pair of speaker , but this , i doubt
that it s in the manufacturer s interest...

Cheers,
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Old 25th June 2012, 07:19 PM   #513
AndrewT is offline AndrewT  Scotland
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One of the audio magazines fairly recently carried out this load current test. The report is linked in this Forum.
They used real music signals fed to three different speakers, specially chosen to be of severe reactance reputation, moderate reactance and a fairly gentle to amplifers.
As far as my reading of the report I came to the conclusion that all three speakers can demand upto five times as much current as the nominal speaker impedance would draw if it were simply a resistance.
That report of 5times made me change my design method of determining temperature de-rated SOAR so that the output stage could cope with 3times for a 100ms period instead of my previous 2times.
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Old 25th June 2012, 07:25 PM   #514
wahab is offline wahab  Algeria
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If 5 times the current is needed then the manufacturer s claim
about his products impedance is a fraud.

I wouldnt brand a speaker that goes down to 1.6R as a 8R product.

Some are stretching the meaning of "nominal" well beyond any
scientific acceptance.
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Old 25th June 2012, 07:27 PM   #515
AndrewT is offline AndrewT  Scotland
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The impedance as seen when fed with a swept sinewave could still be in the 6ohms to 50ohms range for an 8ohms speaker.

It's the reactance to sudden changes in current that create the demand, not fraud.
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Old 25th June 2012, 08:02 PM   #516
KSTR is offline KSTR  Germany
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Quote:
Originally Posted by Edmond Stuart View Post
And finally, I wonder how much amperes you will need to drive 'difficult' speakers with 'difficult' music as well? Maybe 100 A?
Some of the "difficult" speakers may just plainly suffer from inductors going into saturation under rated but worst-case conditions (the most evil signal). We just had a case of that in the lab where a new speaker design with a slightly underspec'd prototype xover kicked a 1.2kW@2R (and 1R capable) amp into current limit (at about 40 amps), at not extemely large SPL (I didn't even need ear protection). Small signal impedance never dipped below 3.2Ohms, though. Best practice is to overspec max inductor current (if not aircore) by a factor of two which regularily leads to 100A figures. Not every product manager is willing to spend the extra expense for that...
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Old 25th June 2012, 08:10 PM   #517
wahab is offline wahab  Algeria
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Originally Posted by KSTR View Post
We just had a case of that in the lab where a new speaker design with a slightly underspec'd prototype xover kicked a 1.2kW@2R (and 1R capable) amp into current limit (at about 40 amps), at not extemely large SPL (I didn't even need ear protection).
Makes you wonder if there wasnt a short on a filter board ,
something like 0.1mm large lost flux solder between two tracks ,
with the amp bursting this local low power low resistance...

40A should do it quite well.....
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Old 25th June 2012, 08:11 PM   #518
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Default fakes

/OT
As for fakes, what about this moron, advertising with 2SJ201/2SK1530 in a TO-220 package.
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Een volk dat voor tirannen zwicht, zal meer dan lijf en
goed verliezen dan dooft het licht…(H.M. van Randwijk)
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Old 25th June 2012, 08:32 PM   #519
KSTR is offline KSTR  Germany
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Quote:
Originally Posted by wahab View Post
Makes you wonder if there wasnt a short on a filter board ,
something like 0.1mm large lost flux solder between two tracks ,
with the amp bursting this local low power low resistance...

40A should do it quite well.....
We checked that and there was no sign of things like that as the speaker behaved exactly as simulated at lower power levels, also the 'scope shots (of speaker current) showed a reproducible sharp increase once the peak current was above 20 amps or so, with a sinewave signal.... now we're building the mass production xo with the best inductors we can find and we'll see... the main culprit was an inductor in a parallel path (to smooth out the 2nd woofer impedance peak to make the xo work at all).
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Old 25th June 2012, 08:38 PM   #520
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Originally Posted by AndrewT View Post
One of the audio magazines fairly recently carried out this load current test. The report is linked in this Forum.
Where please?
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