NuForce: Interesting new digital/switching amp

[Rivendell61]

For those interested in the new 'digital' amps--NuForce are doing something not Tripath, TI, etc. They claim various advantages over current D class products.

http://www.nphysics.com/products.htm

The current amps are 100WRMS monoblocks. >4000 damping. $800 each.

Reviews seem to be very good-- But obviously a work in progress.

These guys are shooting at Bel Canto Evo etc,--not SI.

Go to 'products' on this link:

http://www.nuforce.com/faq/faq-switching-amp.htm

Lots of discussion here (including a lot of manufacturer response):

http://www.audiocircle.com/circles/viewtopic.php?t=17913

(their 5lb, 2000WRMS amp will be out next year....)

Mark

[Deang]

I would stay away from them. The fact that they are charging $20 for a RCA/XLR connector, and $480 for a power cord is reason enough for me.

[dodger]

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On 5/2/2005 6:54:01 AM DeanG wrote:

I would stay away from them. The fact that they are charging $20 for a RCA/XLR connector, and $480 for a power cord is reason enough for me.

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That's roughly about 497 reasons.

[minn_male42]

i have some problems with the power ratings and their "explanantion"

http://www.nuforce.com/products.htm

and then to try to "explain" why only a 100 watts no matter what the impedance.....

Is NuForce's 140W amplifier less or more powerful than a linear solid state or tube amplifier rated for 140W?

In terms of reproducing the dynamics and headrooms of music, the more power the better. The commonly accepted measurement is to rate the output power when the amplifier clips with a 1% THD. Now, what is clipping? Clipping occurs in a linear amplifier when its output signal tries to exceed the limits of its power supply voltage. In a linear amplifier using transistors and bulky a transformer/rectifier, the storage capacitor is recharged only once every 8.33 milliseconds, and its voltage is only slightly above the maximum output voltage, so it could clip rather easily. To put it simply, it has very little headroom. With tube amplifiers, the supply voltage is very high, typically 300 to 600V. Therefore even though tube amplifiers have higher overall distortion, perceptively, they sound more 'powerful'. NuForce's amplifier is a switching amplifier designed with lots of headroom, so that there is no clipping at its rated 140W. Its 140W is perceptively better sounding than a 140W linear amplifier.

b.s.

it is a 100 watt amplifier.... notice how they keep referring to it as a 140 watt amp

[Rivendell61]

Dean,

I agree about the power cord--it is a bit of an eyebrow raiser. But keep in mind they do provide a free power cord with the amp. That Stealth cord is someone elses product.

Regarding the power questions. I can guess the 140WRMS is a residual typo--they originally issued a 70 watt amp and I think intended the next to be 140--but did a 100 instead. Like I said these guys are a work in progress.

See if this quotation answers the impedence question:

"The amp is designed to be an ideal voltage source, and unlike Tripath, we are impervious to speaker load (explain more later). While we can argue about the doubling of power when impedance drops to 2-ohm, we are still talking about measurement using a big load resistor and compare raw voltages. Much like comparing Horsepower without the right context (a 500HP Caterpillar may not run like a 100HP Honda Civic).

For example, without a constant switching frequency and a robust closed-loop response, the Tripath technology will have variable conditions at different frequencies, plus the interaction of impedance at different frequencies, thus resulted in a bit of mess (The Q is all over the place). In NuForce design, the closed-loop response makes sure that at the end of every cycle, the net error is nulled out at a speed of 1Mhz, practically nulls the variance at the speaker terminal, so we behaves closer to ideal voltage source at much higher frequency without running into instability. In conventional Class-D design, you'll notice that many of them open-loop, and have severe phase shift so it has to be strongly filtered at 20Khz to prevent instability.

For more detail, please examine the comparison between various technologies posted in nuforce.com

In the raw power department, we simply put in an off-the-shelf SMPS that is current limited to 100W. So regardless of 8, 4 or 2 ohm, the SMPS will supply 100W of current juice before the current limit kicks in and shuts down the supply. But during the instantaneous peak, we can swing a doubling of power when the speaker impedance halves. If we have a limitless power supply obviously, we can doubling up the power all the way (up to 1152W@2 ohm peak). In fact, one of our OEM application we are driving a pure capacitive load (which is why NuForce amp works exceptionally well with ribbon, and ESL). With our reference speaker, we have been playing music without clipping, with peaks of 300W+ from the 100W amp."

And how come my links do not click??

I have only curiosity about these new amps--by all makers. And have no real interest (or ability) to defend anything. I'll e-mail them and point out the questions--maybe they will respond.

Mark

[minn_male42]

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On 5/2/2005 2:59:08 PM Rivendell61 wrote:

And how come my links do not click??

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you need to be in "rich text" to post links that click.... when you are in the posting screen - click on the the button that says "Use Rich Text"

then when you post a link that you copied from a browser address bar - it will "click" directly from your post on the forum

as for their "explanations"..... it sounds almost like a cable company describing how their power cables sound so much better than a generic power cable....

lots of fluff - but no real substance

and the bit about their "140 watts will sound better than a linear amplifier's 140 watts" is just total b.s.

it might be a great little 100 watt amp..... but they are trying to push it as being much more..... i don't buy it

[Spkrdctr]

Minn Male, there are some serious questions about the concept they explain. I'm not even going to go into this black hole discussion, needless to say, you are on top of it!

Oh heck with it, I can't resist. They say it is two ohm stable until the current limiter kicks in. This is usually not understood well. ANY and ALL amps/recievers can easily drive a two ohm load, including your Aiwa boom box. You control the current with the volume knob. If you do not turn it up, then it will play fine. If you turn it up, you create massive heat and the protection circuits kick in. This is all standard stuff. They may have a novel approach that they have not explained well. But. I'm too lazy and indifferent (apathetic too!) to read through it all.... I'd rather just turn on my Klipsch set up and enjoy......