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Amp limiters... why cant i...?

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JonB67 View Drop Down
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    Posted: 28 December 2018 at 9:41am
Im wondering why people calculate their limiter settings.  

Im not particularly electronics or amp savvy. (Guess i wouldn't need to ask if i was)

Why can't you just unplug the speakers and measure the voltage with the amp set to 11 and dial the limiters down until its acceptable?

Its clearly not this simple as i can't find anyone suggesting this. What am i missing? 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Timebomb Quote  Post ReplyReply Direct Link To This Post Posted: 28 December 2018 at 9:52am
You can and its not a bad way to do it,  worth noting that some amps will drop there output under load more than other amps, ideally its better to do it with the speakers connected, even if its just for a quick check. 

Voltage gain / input sensitivity on amps is normally given at 8 ohms, and can change at 4 ohms and more so at 2 ohms, so calculating limiter settings has its draw backs too...   
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Earplug Quote  Post ReplyReply Direct Link To This Post Posted: 28 December 2018 at 1:06pm
The main problem is that your speaker impedence is a moving target. It will change with frequency, so checking with speakers connected is pretty important. Calculations with a nominal 4 or 8 ohm is just guesswork. And as noted above, most amps will drop a few volts under load.



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Post Options Post Options   Thanks (0) Thanks(0)   Quote Tonskulus Quote  Post ReplyReply Direct Link To This Post Posted: 28 December 2018 at 1:33pm
Having some Tamp TA1400's, they have decent built-in limiters. Great behaviour in stereo (8ohm/ch) mode, limiting output voltage to somewhere around 64Volts/channel. However there is problems when driving low impedance loads / bridge mode @ 8ohm.  Severe clipping may occur as amplifier is unable to give 2x64V=128Volts.  Clipping starts at around 105Volts, long way before limiters will activate..

But as mentioned, speakers has moving impedance with frequency etc so limiting only input voltage is just guessing what happens in output stage..

 





Edited by Tonskulus - 28 December 2018 at 1:46pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote efinque Quote  Post ReplyReply Direct Link To This Post Posted: 28 December 2018 at 2:12pm
I think the problem with limiters is that in addition to catching peaks they flatten the signal as well, which isn't a good thing in the long run... imagine applying a continuous, constant sine wave (or in worst cases near DC) for a prolonged period into a driver..

EDIT : an "ideal" DSP limiter is different of course


Edited by efinque - 28 December 2018 at 2:13pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote kedwardsleisure Quote  Post ReplyReply Direct Link To This Post Posted: 28 December 2018 at 2:25pm
some amp owners manuals do recommend setting limiters up as you say. But I would advise that limiters are no substitute for a proper gain structure as part of a well-matched system which should be done first, then the limiters added as a last resort.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JonB67 Quote  Post ReplyReply Direct Link To This Post Posted: 28 December 2018 at 5:18pm
Originally posted by efinque efinque wrote:

I think the problem with limiters is that in addition to catching peaks they flatten the signal as well, which isn't a good thing in the long run... imagine applying a continuous, constant sine wave (or in worst cases near DC) for a prolonged period into a driver..

EDIT : an "ideal" DSP limiter is different of course

Did you even read my question? 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JonB67 Quote  Post ReplyReply Direct Link To This Post Posted: 28 December 2018 at 5:19pm
Ok. I'm up for trying this. 

Is there a guide or how to anywhere?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote efinque Quote  Post ReplyReply Direct Link To This Post Posted: 28 December 2018 at 6:10pm
Originally posted by JonB67 JonB67 wrote:

Did you even read my question?

You'd probably need a very accurate multimeter or an oscilloscope... I remember we had those old analog meters in school for the purpose of measuring peaks/other anomalies because they can sometimes show things DMMs don't.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JonB67 Quote  Post ReplyReply Direct Link To This Post Posted: 28 December 2018 at 6:47pm
Why would it have to be super accurate?

Ive got a fluke multimeter which will probably be sufficient,  but i wonder why you think it needs to be particularly accurate. Can you show me your workings?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote efinque Quote  Post ReplyReply Direct Link To This Post Posted: 28 December 2018 at 7:08pm
Originally posted by JonB67 JonB67 wrote:

Why would it have to be super accurate?

Ive got a fluke multimeter which will probably be sufficient,  but i wonder why you think it needs to be particularly accurate. Can you show me your workings?

I think the logic board/LCD in handheld DMMs is too slow to react to sudden changes in voltages.

It also took me some time to realise the fact that program material and test tones are two different things (I've ran 100, 1k and 10kHz tones through a filter and measured the outputs with a DMM.. haven't done the same with a limiter, with the one I built for a crossover I just checked the emitter output whether it bleeds the operating voltage so I don't break things like headphones)


Edited by efinque - 28 December 2018 at 7:10pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JonB67 Quote  Post ReplyReply Direct Link To This Post Posted: 28 December 2018 at 8:53pm
Originally posted by efinque efinque wrote:

Originally posted by JonB67 JonB67 wrote:

Why would it have to be super accurate?

Ive got a fluke multimeter which will probably be sufficient,  but i wonder why you think it needs to be particularly accurate. Can you show me your workings?

I think the logic board/LCD in handheld DMMs is too slow to react to sudden changes in voltages.

You think, or it is? Show me facts not guesswork.
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