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Old 3rd May 2009, 10:52 AM   #1
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Default amplifier protection

here we go .....

i often stated my opinion that many of the amps presented in the forum might be wonderfull audiofile ( he he ) amplifiers but if the use is not casual listenig but small PA application or in a few words 100% power for quiet long time many of these amps will not make it

HOW DO YOU PROTECT AN AMPLIFIER FROM ABUSE ?????

---- there is a post i made about VI limmiters but it doenst seem to get anywhere since VI limmiters are well known sonic killers but then the question comes does it worth to loose some of your sonics to gain more safety ?????

---- then underdesign the power supply so at full power rails dive doesnt sound like a solution since that will distort like hell

----- overdesign of the all amp when you need 3 pairs of outs to actualy use 5 to be on the safe side might works but there you get a cost issue

------ use optocoupler circuit to reduce or compress input signal ( seen it working very well in ACoustica amps but sound is not that perfect )


so whats the catch here ???? how can you moove in the midle ???? what is the golden solution ????

be aware now people ..... one way or another in some time in its life every amp will be abused either on purpus or accident

in this case abuse is a fact ....

all input is very welcome

thanks for your time
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Old 3rd May 2009, 11:09 AM   #2
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I think the first decision to make is: can you accept that the amp shuts down once in a while when overloaded? Or do you want the amp to absolutely continue playing in overload case?

If the latter is required, then you will always have a system that distorts because you want the amp to continue to play when the protection activates, whatever that protection is.

If you can accept momentary shut off, then the protection can be absolutely inaudible (until it shuts down of course).

Generally, in PA, you wouldn't accept shut-down. On the other hand, in PA, you probably don't require the absolute transparancy either.

Jan Didden
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Old 4th May 2009, 07:37 AM   #3
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Default interessting comment

Quote:
Originally posted by janneman
I think the first decision to make is: can you accept that the amp shuts down once in a while when overloaded? Or do you want the amp to absolutely continue playing in overload case?

If the latter is required, then you will always have a system that distorts because you want the amp to continue to play when the protection activates, whatever that protection is.

If you can accept momentary shut off, then the protection can be absolutely inaudible (until it shuts down of course).

Generally, in PA, you wouldn't accept shut-down. On the other hand, in PA, you probably don't require the absolute transparancy either.

Jan Didden
but NO .....shut down is not an option .....
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Old 4th May 2009, 08:32 AM   #4
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Default Re: interessting comment

Quote:
Originally posted by sakis


but NO .....shut down is not an option .....

OK, fair enough. But then you have to be prepared to accept some non-linearity in case the protection activates. But with a good design it will hardly be audible, also because it will be at very high levels anyway where speaker distortion will already be horrible probably.

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Old 4th May 2009, 08:39 AM   #5
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Default well not exactly

jan ..... it doesnt mean that all pA application have dirty sound ..... ha ha ha

then yes if protection of any form is activated you expect to have some sound effect also

i thing that all this starts to lean on VI limmiters but they have to be kinda sophisticated
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Old 4th May 2009, 09:09 AM   #6
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Default Re: well not exactly

Quote:
Originally posted by sakis
jan ..... it doesnt mean that all pA application have dirty sound ..... ha ha ha

then yes if protection of any form is activated you expect to have some sound effect also

i thing that all this starts to lean on VI limmiters but they have to be kinda sophisticated

Oh no, I don't mean PA sound is always bad. It's just that the some of the subleties we worry about in home hifi probably don't play a role in PA, that's all.

BTW Did you read Mike K's EW article on VI limiting?

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Old 4th May 2009, 10:16 AM   #7
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Default haven't find

this article yet ....hopefully somebody will point me a link

also ithe post i ve made i was expecting to see some optocoupler made with schematic but nothing so far ....

regards sakis
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Old 4th May 2009, 10:20 AM   #8
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The technology (optocoupler or something else) is secondary. The important issue is at what point you want the protection to activate, how sharp or smooth, that kind of thing. Do you want the protection to be faster at low freq and allow more hi-freq?
You can always scale it with the number of output devices and use your favorite technology.

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Old 4th May 2009, 10:33 AM   #9
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Default jan .....

that is very interesting ....

i think that i ve never seen VI limmiters that are frequency depenting ....

to specify this i thing that it can be sumarized in a few points

-----DC protection ...i find it most of the times not needed i think that crow bar will be the best since if outputs are gone there is no problem to blow the fuse

-----then VI limiters have to be there but if possible not to effect sonics up to some point

-----finally i think that input compression of any form will require overdesign since if the input is compressed means that amp will work at 100% at all times ( classic abuse form )
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Old 4th May 2009, 10:48 AM   #10
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Input limiters/compressors are mandatory for PA. In case of clipping, output current limiting, too high average output power (also for speaker protection) or overheating, they are activated to progressively attenuate input signal until the problem is solved.

Only other more severe faults like mains overvoltage or undervoltage, RF on the input or output, DC on the output or persistent current limiting (a short circuit load) should cause a PA amplifier to shut down.
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