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'burst' power for torroidal amps?

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darkmatter View Drop Down
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    Posted: 08 May 2009 at 3:20pm
something i was wondering about the other day - in class D amps the burst specs can differ wildly from the long term rated output power. in torroidal supplies can the same thing happen?

i.e. if a torroidal amp is rated at 150 watts, could it put out 300w for brief periods of time by emptying it's caps? or would limiting mechanisms usually kick in first?

cheersSmile
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Timebomb Quote  Post ReplyReply Direct Link To This Post Posted: 08 May 2009 at 3:28pm
Depends on the amp and how it was specced but yes.   EP2500s will do there 1200W burst into 2 ohms, but long term is about 750W per channel before it trips the 8A breaker.  Will do the same thing at 8 ohms and 4 ohms, but to a lesser extent.   
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Post Options Post Options   Thanks (0) Thanks(0)   Quote darkmatter Quote  Post ReplyReply Direct Link To This Post Posted: 08 May 2009 at 3:34pm
Cheers man. So as long as I don't overdrive it a well made amp using over-specced parts in the right topology could well be enough to drive comps, even if the specs don't suggest it has the '4 x the rated power' that some people would recommend using. Fingers crossed anywaysLOL
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Timebomb Quote  Post ReplyReply Direct Link To This Post Posted: 08 May 2009 at 3:41pm
Matrix UKP500 sounds bang on for driving compression drivers, i have a little mosfet amp of similar power and ive never blown a compression driver with it.  Above 25KHz theres not much constant power in most music, its all transiants, so your never really feeding the driver 150W long term.  Clipping is the thing that tends to kill compression drivers. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote levyte357 Quote  Post ReplyReply Direct Link To This Post Posted: 08 May 2009 at 3:50pm
Originally posted by darkmatter darkmatter wrote:

Cheers man. So as long as I don't overdrive it a well made amp using over-specced parts in the right topology could well be enough to drive comps, even if the specs don't suggest it has the '4 x the rated power' that some people would recommend using. Fingers crossed anywaysLOL


The Cmark 2650 will easily power any 3x compression drivers per channel @ 1k-16k.

However some amps are better 1k-16K, than 30-100Hz.Wink
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Elliot Thompson Quote  Post ReplyReply Direct Link To This Post Posted: 08 May 2009 at 4:13pm

Originally posted by Timebomb Timebomb wrote:

Depends on the amp and how it was specced but yes.   EP2500s will
do there 1200W burst into 2 ohms, but long term is about 750W per
channel before it trips the 8A breaker.  Will do the same thing at
8 ohms and 4 ohms, but to a lesser extent.   


Are you sure that is correct?

As far as I know Peak is half the RMS. So, if an amplifier delivers 700 watts RMS continuous @ 4 ohms, it will give 1400 watts Peak or burst. The limiting factor would be the power supply if those numbers cannot be met in a 2-ohm load.

52.9 volts (699 watts) RMS is 74.8 volts (1398 watts) Peak under a 4-ohm load.


I've seen a bench test result on the EP 2500 stating it offers 1000 watts per channel @ 2 ohms. That is not using burst signals either. While it is 200 watts short of 1200 watts @ 2 ohms, it meets its stated specs in 4 and 8-ohm loads.

The biggest issue when benching 2-ohm loads is having the proper current to feed the amplifier providing, the power supply is strong enough to do it.

Best Regards,
Elliot Thompson
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Timebomb Quote  Post ReplyReply Direct Link To This Post Posted: 08 May 2009 at 8:34pm
I assume that was a typo, you mean peak is twice the RMS , "peak" genrally means calculateing power from the peak voltage. "burst power" is genrally means the RMS power (from RMS voltage not peak) that can be sustaind for short transiants, genrally 10ms - 1s.   Burst and peak are not the same thing.

Yeah the reason it cant sustain its output in 2 ohms for very long is the supply cant handle it it trys to draw too much current, 1000w sustained per channel is good going, is that both channels driven? 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Elliot Thompson Quote  Post ReplyReply Direct Link To This Post Posted: 08 May 2009 at 10:39pm


Originally posted by Timebomb Timebomb wrote:

I assume that was a typo, you mean peak is twice the RMS , "peak"
genrally means calculateing power from the peak voltage. "burst power"
is genrally means the RMS power (from RMS voltage not peak) that can be
sustaind for short transiants, genrally 10ms - 1s.   Burst
and peak are not the same thing.


My apologies!

That is what I meant.

Originally posted by Timebomb Timebomb wrote:


Yeah the reason it cant sustain its output in 2 ohms for very long is
the supply cant handle it it trys to draw too much current, 1000w
sustained per channel is good going, is that both channels driven? 



I am more than certain it was not both channels driven for that would be 44 amperes @ 2 ohms. The only amplifiers I would say that could do both channels driven @ 2 ohms using sine waves are the old amplifiers that many cry about because they are too heavy.

However, each channel did manage to reach over 1000 watts @ 2 ohms. Distortion rating is under 1%. I would imagine he is a traditionalist and don’t fancy 1% THD measurements that is common when measuring professional amplifiers @ 2 ohms using a 1 kHz sine wave.







Quote
I found heat and the circuit breaker located in the amplifier to be the 2 items that caused the amplifiers to fail the tests and not meet the published specs. I almost opened up the 2500 and bypassed the circuit breaker just to see if it would go on or go up in smoke. If I had a room that was temperature controlled to about 70 degrees with heavy duty air handling capabilities (and a duct pointed right at the intake of the amp), the amp would not have gotten so hot, so quick. Even with all that these amplifiers will not run with a sine wave at full power at 1 KHz for more than 5 minutes under any load, 2, 4, 8, or bridged! They are just not made to run like that. On the other hand, if you were to derate the power of the units, they could run all day at rated specs.


http://www.avsforum.com/avs-vb/showthread.php?p=10755537#post10755537


Best Regards,


Edited by Elliot Thompson - 08 May 2009 at 10:40pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Timebomb Quote  Post ReplyReply Direct Link To This Post Posted: 09 May 2009 at 12:45am
Interesting, i see the tests done at 120V from a variac, id guess thats US voltage, does the US behringer have a 16A breaker on it?  We get 230V and a 8A breaker on an EP2500 so that accounts for a some of the difference.

Also i think it dependes on what you consider to be long term RMS output,  10 seconds might not trip the breaker, but 60 seconds might.

I vaguly remember reading this avsforum tread before, does it say anywhere how long the test signal lasted for?  

    
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Post Options Post Options   Thanks (0) Thanks(0)   Quote fredos666 Quote  Post ReplyReply Direct Link To This Post Posted: 09 May 2009 at 3:34pm

I think that nobody really understand what's a burst signal.....This is not just a peak or a ''shot'' that you send to the amplifier...A burst signal is a continuous sine wave with determined ''on'' and ''off'' period. The burst power is always the same as RMS power IF the power source is regulated. Under unregulated source, the burst power could be a bit more than the RMS value. The only reason why you see so many burst power rated amplifier is about their thermal ability to dissipate the heat. The burst power is nearly an image of a normal music program when it have a period of 1/8 of the time. At 1/3 of the time, it's like a heavy compressed near clipping program.

 

About peak power, it's normaly the power you get with hard clipping and it equal the power supply rail. Many cheap manufacturer rate their amp as peak power, 1Ch driven, at nominal power source with only 1 burst (shot) of 1-2 cycle of a sine wave....Be award!

In ''résumé'' (I spaek french!):

 

-Burst power is nearly the same value of RMS power

-Peak power is the maximum continuous power when you dont take care about distortion, and is normaly used to determine the headroom of and amplifier, ie some amplifier rated at 100W 8ohms use a +/- 40V power supply, that's mean 200W into 8 ohms peak power. Another 100W amp use +/- 50V power supply, but with less capacity. It will reach 300W peak. First amp have 3db headroom and second 4.5db. Personaly, I will prefered second amp....

-1000W peak power stated on a 200$ amp is bullsh*t...But maybe the EP2500 is the exception...
 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote darkmatter Quote  Post ReplyReply Direct Link To This Post Posted: 09 May 2009 at 3:54pm
Thanks for clarifying fredos, really helpful!

It sounds like I'm using the wrong term then. What I was asking is whether the amplifier would put out well over it's rated power for an instant if it's using energy stored in the capacitors on the output rails. i.e. before it's trying to draw any more from the power supply. The question applies specifically to amplifying frequencies above 1khz I guess, just wondering whether transients can be accurately reproduced in this way.

In English we'd say "to recap" in case you were wonderingWink
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Elliot Thompson Quote  Post ReplyReply Direct Link To This Post Posted: 09 May 2009 at 5:38pm
Originally posted by Timebomb Timebomb wrote:

Interesting, i see the tests done at 120V from a variac, id guess thats US voltage, does the US behringer have a 16A breaker on it?  We get 230V and a 8A breaker on an EP2500 so that accounts for a some of the difference.

Also i think it dependes on what you consider to be long term RMS output,  10 seconds might not trip the breaker, but 60 seconds might.

I vaguly remember reading this avsforum tread before, does it say anywhere how long the test signal lasted for?  

    


I would need to check my EP 2500 to make sure but I do believe the breaker is 15 amperes. The 120-volt standard in the States is precisely the reason why I configured my MA 5000vzs to 240 volts.

 

They have many inexperienced guys trying to operate medium to large amplifiers (3000 watts and up) on 15 (1800 watt) or 20-A (2400 watt) wall receptacles.

 

For me, long-term is until I shut the amplifier off. I have an old Crest 5000 that offers two 2 KVA Transformers. It is rated using continuous average sine wave over a bandwidth from 10 – 20 kHz in 8, 4 and, 2-ohms. However it weighs 36 kg and house 4 rack spaces. Amplifiers of that calibre would always deliver their advertised watts until you shut it off.

 

Today, things are different. Many want lightweight, smaller rack space units. For such requirements compromise (in the power supply) is in order.

 

If you go to the beginning of the topic, you will notice that amplifier is one out of many amplifiers tested. You will need to read it all it to find out how long each one was tested.

Best Regards,


Elliot Thompson
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