"High Current"

Sean...To achieve the "doubling down" at clipping which you describe requires a substantial increase in the power supply cost. It is not a characteristic that is particularly useful in the home audio situation, where amps are not driven to clipping. (Pro sound is a different situation). While you are technically correct, I think that the law of diminishing returns comes into play here.

Again from my military electronics experience...when I went to work in 1961 "built to mil specs" really meant "overdesigned", and the poor taxpayer paid the bill. Recently we have built even the most complex military systems (such as a Fire Control System to prepare and lauch 24 ICBM) by assembling Commercial Off The Shelf (COTS) hardware. That old custom designed stuff was interesting work for the engineers, but common sense prevails.

Two equations tell the entire story. Watts=VoltagexCurrent, and Watts=Current(squared)x Resistance.

So as has been stated earlier an amp that is not current limited will double its power as the impedence is halved. So if an amp is rated at 200 watts into 8 ohms it must produce 400 watts into 4 ohms and 800 watts into 2 ohms.

But that really is only half of the story. To answer the question about how this impacts the sound you have to know what the impedance curve is for the speakers you have. I used to own Thiel 3.6s. They are nominally 4 ohm speakers but there is a point in the lower midrange where they dip to about 2 ohms as I recall. That means if you are driving a current limited amp (say 100 watt into 4 ohms rated amp) close to its limit, the speakers will be demanding 200 watts in this midbass region. If the 100 watt amp is only rated at 150watts into 2 ohms you could be running into clipping and a clear audio distortion. So high current designs are not necessarily required for many well behaved speakers. There are lots of high end speakers some cause trouble other wont.

Gregm,

The Krell Class A "Full Power Balanced" cx-series "double-down"
all the way to 2 ohms.

Take the "baby" of that line-the FPB-300cx: 300 wpc at 8 ohms,
600 wpc at 4 ohms, and 1200 wpc at 2 ohms. See:

http://www.krellonline.com/html/m_ClassA_p_FPBs_300cx.html

Dr. Gregory Greenman
Physicist

Morbius: Those are typical factory specs, nothing like what we are discussing here. On top of that, the voltage swing on that specific Krell is pretty low at their rated 138 v peak to peak. My Perreaux PMF-3150, which is also rated at 300 wpc @ 8 ohms, is rated at 180 v peak to peak. I would like to see what the Krell REALLY clips at into various loads. I have NO doubt that it is a sturdy amp, but exactly how sturdy, i don't know.

As a general rule, so long as current levels are reasonably up to snuff, the amp with the highest rail voltages will typically sound the cleanest and least compressed when driven hard. This is why tubes, with their very high plate voltages, can work quite well. This is true even though they are typically quite current limited in comparison to a "big brute" SS amp. The reason? So long as they have "enough" current to deal with the speaker load at hand, they've always got gobs of headroom due to the high rail voltages. Sean
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The reason current is the issue is that high rail voltages collapse under demand and low impedences. Hi voltage measured with high impedence has nothing to do with an amps performance.