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Old 16th January 2006, 11:36 AM   #11
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Quote:
Originally posted by quasi
The power supply capability holds some of the answer. A power supply sized for home use will collapse sufficiently to offer some self-protection. A power supply in a PA amp is usually stronger and likely to hold voltage better, good for the sound but bad for the FETs.

Cheers

The Present Trend of PA amp Power Supply isn't stronger one..
The PA amp manufactures uses under powered supplies...In the event of 8 ohm load for a typical 1200@2ohm amp the rails are at +-110..gradually upon loading with 4 ohms these sag to +-85V then again to +-70V at 2 ohms load..this type of setup has an advantage of 2 times the peak power for a given rms watts for short periods of time brusts you can say..and close spacing of power amp wattage at different load impedances..
lets say in present day scenario in PA amps..
1200W--2ohms
850W--4ohms
600W--8ohms...
not like 1200W--2 ohms, 600W at 4ohms...350W --8 ohms...with stiff power supplies...time has changed...less weight of amps..highest peak power of music signal brust...close power specs with impedance variations...alike
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Old 16th January 2006, 11:48 AM   #12
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Quote:
Originally posted by quasi
As a perspective, most domestic amplifiers I've seen to date would fail the SOAR calculations I have used here.
Quasi Aussi One,
what do you reckon is the slack because of square wave testing the SOA ?
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Old 16th January 2006, 11:51 AM   #13
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Default 10-9 Jacco V 1?

I'm not sure what you mean by slack?
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Old 16th January 2006, 11:58 AM   #14
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Q, slack as in reserve.
How much more favorable would the SOA curve be if not square waves would have been used but sinus waves ?
Who will test a domestic amplifier with a square wave input and a 2 ohms dummy load ?
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Old 16th January 2006, 12:04 PM   #15
quasi is offline quasi  Australia
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Quote:
Originally posted by jacco vermeulen
Q, slack as in reserve.
How much more favorable would the SOA curve be if not square waves would have been used but sinus waves ?
Who will test a domestic amplifier with a square wave input and a 2 ohms dummy load ?

Hmm...I don't know.

I suspect a manufacturer would rather test into a 2 ohm resistive load with a square wave than a sine wave...
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Old 16th January 2006, 12:05 PM   #16
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Quote:
Originally posted by jacco vermeulen
Q, slack as in reserve.
How much more favorable would the SOA curve be if not square waves would have been used but sinus waves ?
Who will test a domestic amplifier with a square wave input and a 2 ohms dummy load ?

Hi Jacco ,

Square wave testing would not let you to test the sustainance of amp in 2 ohms load..its a very light load...
For Real Hardcore Testing Use a Highly Reactive 2 ohms load and drive the amp with Sinewaves....
A 1mH in series and 22MFD in shunt with 2 ohms resistor will do the fine job....

K a n w a r
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Old 16th January 2006, 12:05 PM   #17
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Hey Kanwar ...where did your post go ???

aaaahh there it is .....foiled by the edit button again.
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Old 16th January 2006, 12:10 PM   #18
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Quote:
Originally posted by Workhorse
For Real Hardcore Testing Use a Highly Reactive 2 ohms load and drive the amp with Sinewaves
Kanwar,
have you done that and how does it relate to the SOA curve ?
1 on 1 ?
Device number is corrected for low resistance load, and for reactance.
But the correction is placed on the datasheet SOA curve, which is a square wave measure.
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Old 16th January 2006, 12:35 PM   #19
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Hi Jacco...
Yes I have done these test...on my NVMOS amps..

There is a Story behind it....
In my early explorations..When I first designed an amp with 500WRMS@4ohms...Set the current trip shutdown threshold at 22amps peak...Then we took it in a DJ party.. when operating in a program with the usual heavy BASS & Treble CD music ..there wasnot any tripping ..suddenly the main singer came to the stage and started singing...and within few seconds the amp was tripping due to excess current..demand because of a vocal singer voice in live arena.....Everything was out of my understanding...what was happened...Then i remove the trip sensor and the amp functions effortlessly till after 1 hour it gets somked...into fire...due to this singer's voice ...

next day i invited the singer into my place and again repeated the program excatly but with intruments attached for monitoring what was happened....
I was amazed that the peak current demand into typical 2 X 15"4 ohms speaker was 35amperes peak..much greater than what i thought during the vocal sessions....then dismantles the speaker,,a normal crossover was found which poses the highly reactive load when only the mid frequency were fed during the singer singing the vocal....

The amp was observing both Highly peak current drive and highly reactive drive simuntaneously ..the reactive load forces the OFF FET to pass as much as 10 amperes at its max VCC which was 70V ...instant dissipation was 10X70=700W....which insist that paralleling must be done inorder to sustain the operation....
Then to check this validity I run the same procedure on the another amp which was Studiomaster 2000E....upon encountering that load this amp limits it current heavily and distorts the sound very much..... hwereas our prototype does the job fine with more parallelled output fets..

From That Day I constructed a Reference Reactive load which was to be used as a testing measure for my amps.....
During Highly reactive loads...The SOA must be observed with FULL VCC accross the FET Drain to Source and its ability to pass the max current at that point must be considered when driving it with reactive loads....I choose the value of max reactive current equals One Third of Peak current into pure resistive load...per FET at Given VCC....
Lets say if peak current capability is 10 amperes then reactive current capability of the output stage must be at least 3.33 amperes...or it would not survive...Some users prefer VI limiting...I dont like it because it heavily distorts the sound....


K a n w a r
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Old 16th January 2006, 02:42 PM   #20
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Hi, Kanwar,

Quote:
.. when operating in a program with the usual heavy BASS & Treble CD music ..there wasnot any tripping ..suddenly the main singer came to the stage and started singing...and within few seconds the amp was tripping due to excess current..demand because of a vocal singer voice in live arena.....Everything was out of my understanding...what was happened...
I experienced the same thing here in my workdesk. I've noticed it for a long-long time, but I'm not sure what is happening until you write that. I think it has to do with resonance with passive Xover or/and the speaker, but I haven't research it.

I notice that when I play Disco music with full bass, the whole system is not sucking current as much as if the music played is only a female voice.

Female voice is much more a "sucker" than bass tones
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