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Old 23rd November 2001, 09:30 AM   #1
pkgum is offline pkgum  Australia
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what does power bandwidth mean in this webpage? If it is not frequency response then what is it?
http://www.classic-audio.com/marantz/0250.html
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Old 23rd November 2001, 10:03 AM   #2
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Power Bandwidth - frequency response over which the amp can produce at or near rated power .........
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Old 23rd November 2001, 11:31 AM   #3
pkgum is offline pkgum  Australia
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thx

another question

if the power goes down in the amp...does the frequnecy response spread out more?

e.g
power bandwidth at max power = 20Hz - 20Khz
Frequency response at a lesser power = 10Hz - 40KHz
Frequency response at an even lesser power = 5Hz - 60KHz
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Old 23rd November 2001, 11:48 AM   #4
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yes this is usually the case but you have to severely reduce the output power to get such an effect and you will find that the low end stops going any lower at about 10Hz as the high pass filter of the amp really starts to kick in and stop it from trying to amplify infra-sound which is not only potentially damaging, it can be deadly if loud enough.

[Edited by AudioFreak on 11-23-2001 at 06:56 AM]
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Old 23rd November 2001, 12:18 PM   #5
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Conventionally, power bandwidth refers to the frequency response of the amplifier at -3db output power ie., half the rated power.

Note that in general, Voltage Feedback amplifiers have a rather low frequency response in open loop and the response gets extended when the loop is closed. On the contrary, Current Feedback amplifiers have a higher open loop bandwidth, often higher than the audio band which gets extended further on applying feedback.

In Voltage Feedback amplifiers, very high open loop gain and very low open loop bandwith, operated with a high Negative Feedback factor CAN lead to high levels of Transient Intermodulation Distortion. Power bandwidth does reflect a lot about how an amp might sound, although it is not the only parameter.
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Old 23rd November 2001, 07:05 PM   #6
pkgum is offline pkgum  Australia
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then what is the average power bandwidth for a good power amp?
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Old 24th November 2001, 01:00 PM   #7
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From experience, it seems the lower cut off frequency should be <10Hz and the higher cut off frequency about 100KHz or more is fine.

If the lower cut off frequency is higher than this, it causes a significant phase shift in the low frequency spectrum.

Generally amplifiers that have a higher cut off around 20KHz, dont't sound "airy" as compared to amplifiers that have a higher bandwidth. I repeat, generally...

Then there are cases where you have to deliberately lower the hf cutoff, to prevent TIM and RF interference.

If I am not mistaken, the Alephs have a bandwidth extending from near DC to about 100KHz. That should about give you an idea.
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Old 25th November 2001, 03:08 AM   #8
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I measured my Aleph 2s out to about 130-140kHz (I think--I'm quoting from memory) at low power. My tube amps are good to about 135kHz, again at low power.
At high power, the response will draw in, sometimes dramatically. Go look up a Bode plot to help visualize this effect.

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