"High Current"

Sean, IS it possible to manufacture an amp for home use that doubles down at clipping to, say, 2ohms??
I'm not sure, but i think it's theoretically very dificult?
Cheers

The Sunfire amps can do this with enough AC and the right internal fusing. I've got test results from an old magazine review on one of the original Sunfire's that verifies this. I'm not saying that i consider the Sunfire's to be the "best built" ( NOT by a longshot ), "built like a tank" ( they aren't ) or "the best sounding" ( no way ). What i am saying is that if Bob Carver could do this 10 years ago, i don't see any reason why others can't now. Especially "big name" amps that cost WAY more money and weigh two or three times as much.

One should bare in mind that this is NOT a "little" amp either. We are talking about a product rated at 300 wpc @ 8 & 600 wpc @ 4. For the record, this amp EASILY beat the factory ratings too, producing well over 700 wpc at clipping into 4 ohms and almost 1500 wpc into 2 ohms. I can provide the specific figures if someone is really interested, but i'll have to dig them up.

How much easier should it be to achieve similar results when starting off with a much smaller amp that needs less current, not as much of an output stage and even less heatsinking? There really is NO excuse for something like this other than cut-corner production and less than optimal design. Sean
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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