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Old 9th January 2004, 02:00 AM   #11
jwb is offline jwb  United States
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The short explanation is this: the amplifier's power is limited by two curves: Irms^2*R and Vrms^2/R. If you plot these two curves, the amplifier must be operating in the area under the curves. Where the curves intersect is the maximum power.

Here is the plot for my Aleph-X amps with 14V rails and 1.54A idle current per side. The blue line is the current limit, the red line is the voltage limit. If you can replicate this plot, you will have a good understanding of amplifier power and load impedance.

PS: I consider this a 40W amplifier.
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Old 9th January 2004, 04:31 PM   #12
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Thanks to panelhead and to jwb for the explanations. It is a tough row to hoe, but some of this stuff is beginning to make sense to me! As Harry Connick, Jr. (and maybe Bobby Darin before him) sang: "I'm beginning to see the light". From jwb's graph I infer that any given amp/setting has a well defined operating area, if that's what you call it. Panelheads arithmetic leads me to conclude that amps designed to stay tough into low impedances must have prodigious bias current (current capability?). I am reminded of a statement that Nelson made in the A-75 article, something like: 'we know that about a hundred of you will write in and ask how to bias the amplifier for class A in 1 ohm'.

Larry Wright
Seattle area
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Old 9th January 2004, 05:20 PM   #13
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Quote:
Originally posted by Zapped
Thanks to panelhead and to jwb for the explanations. It is a tough row to hoe, but some of this stuff is beginning to make sense to me! As Harry Connick, Jr. (and maybe Bobby Darin before him) sang: "I'm beginning to see the light". From jwb's graph I infer that any given amp/setting has a well defined operating area, if that's what you call it. Panelheads arithmetic leads me to conclude that amps designed to stay tough into low impedances must have prodigious bias current (current capability?). I am reminded of a statement that Nelson made in the A-75 article, something like: 'we know that about a hundred of you will write in and ask how to bias the amplifier for class A in 1 ohm'.

Larry Wright
Seattle area

There is an even bigger issue here also. A 4 ohm rated speaker usually has the impedance vary from 2.8 ohms to 20 ohms or so across the audio spectrum.
Plugging all those real impedances into the equations make the math worse than my confusing examples.

George
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Old 9th January 2004, 05:27 PM   #14
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For me, its easier. I have one set of Maggie MG II-A's with 6 ohm purely resistive impedance, and one set of Maggie MG-12's, with 4 ohm purely resistive impedance. So your equations have made things much easier for me to figure out which way to go. ( Both systems are bi-amped with a subwoofer, so power in the deep base regions is not a big issue either. )

Larry Wright
Seattle area
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Old 9th January 2004, 06:10 PM   #15
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In many systems, the lowest impedances are found in areas
where the audio power is likely to be quite low, for example
below 20 Hz and above 10 KHz, and so this is not usually a
real problem.
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Old 10th January 2004, 02:03 PM   #16
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Ok, thank you all for your help. Now I'll try to make a schematic.

AudioAngel
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