NAIM Poweramp power output

I am sure someone more technically astute can give a better answer. The 500 is a “bridged design” which apparently boosts the power available. The NAP 300 swings about +/-25 amps which also helps with difficult speaker loads.

One bit of "hidden magic" may be down to their regulated design - OK, not so hidden if the cover's off the amp!  A regulated power amp is a very rare thing - essentially you have two power amps in one case where one "amp" regulates the other - and the NAP250, NAP300 and NAP500 are some of the only such amps available.  A fully regulated amp remains very "stiff" even when the demands placed upon it would have an unregulated amp on the slide.  It means that within its operating envelope you get very consistent high performance.  Regulated amps are very tricky to get right and that may explain why they are so rare.  However, they are something of a Naim speciality, the regulated NAP250 (nee 200) having been a key Naim product from the very beginning.

Of course, the best way to fully appreciate the "hidden magic" of a Naim amp is to not pay too much attention to the numbers and just listen for yourself.

Richard is right, there's a lot more to an amp than sustained power / current output: particularly the transient performance and tolerance to load phase characteristics (aided by the 'stiff' design); and the best way for most people (amplifier designers excepted) to appreciate the nuances of transient performance and the other less obvious aspects of amp design...

is to listen.

On a Nap 500, the  bridge design was done to eliminate the return currents from the speaker on the negative terminal polluting the signal earth.

On a NAP 300 vs 250 , the transformer emits a very strong magnetic field which affects the audio circuits. The 300 has a separate PSU, and the delicate audio circuits including those mighty custom designed high current 007 and 009 transistors and kept in a separate chassis and box.

the NAP 250 has everything in one box, but hey I still love my Nap250 Dr very much as it sounds fantastic to my ears, and do not plan to upgrade..... I don't like messing around with Burndy cables.... 

I suspect there is an engineering answer to the question.  I don't know what it is, but I suspect it's to do with max current delivery as the load impedance approaches zero (impossible, but "in the limit").  The 500 has a higher continuous power output into 8 ohms than the 250 but something common to both amps appears to be limiting the maximum current as the load impedance approaches zero (OK, 1 ohm).

Anybody know what this is?

Yes I do know what it is: it's the dynamic (i.e. transient) capabilities of the amp, combined with the ability to react to very small changes in a amongst much larger signal.

As Richard says - listen to them.

All NAIM power amps are "capable" of much more then their specification on paper.

Douglas.

Douglas - this is specifically what I am trying to understand... capable of what?

Background is that I am currently running a NAC272 + XPS DR driving a Bryston 4BSST2 - which puts out 360W/570W into 8/4 OHM and under dynamic conditions it delivers 480W/900W/1595W/2160W into 8/4/2/1 OHM... or max current of 46.5A.

I am considering the next upgrade and since there is currently no follow-on to the NAC 272, I am considering upgrading the streaming side to a NDX2 (when it becomes available) - but that will mean that I will need to buy a pre-amp - something like a NAC 252 - which will needs a power supply and 'different' connections if I wanted to drive a non-NAIM power amp. So I am looking at the NAIM power amps as well - and I was considering the NAP300 or potentially a NAP500 (but that would mean looking a 2nd hand version due to the costs)... but the NAP 300 does not look that powerful (on paper at least) vs what I currently have...

Hence why I am looking at the Poweramp side of things and trying to understand why/if NAIM poweramps are more powerful than they may first appear.

My speakers are rated at 4 OHM and I know that their min impedance can drop down to below 2 OHMs... curretly my Bryston has no trouble driving these speakers at all - even driving the speakers  hard, the Bryston only get slightly warm... but I believe that the NDX2 will (or potentially a 2nd user or ex-demo NDS) will give me a better sound - but this opens up the whole question  of pre-amps and associated power amps.... or do I wait for the yet announced follow-on for the N272 (maybe there will never be one...!!!)

I am looking to see if I can find a dealer who has my speakers, a NAP300/NAC252 and a NAC272 with XPS and a Bryston 4BSST to try ad listen for myself - but this is becoming difficult....

I think you are missing the point. In my early days the Naim amps were nothing more than a shoe box with 15 or 20 watts output. I turn up for a demo of a more muscular 50watt  amp, and end up buying the so called “little guy” in a shoe box, because it sounded great. Nothing has really changed........listen, then buy.

Fernar, according to your profile you are running some quite demanding speakers, but first, it is not essential to run a Naim power amp with a Naim source. Second, if you do, find a good Naim dealer, take their advice, and listen for yourself before deciding. The source upgrade you are planning should bring big improvements, too. 

The size of the transformer makes the difference. Larger transfos have more torque, just like displacement in a car engine. 

With a linear power supply amplifier, Naim or others, the weight of the amplifier tells a lot about it's driving ability.

douglas posted:

All NAIM power amps are "capable" of much more then their specification on paper.

 

Douglas.

If by capable you mean power capability, I think that in absolute terms that is a fallacy - apart from anything else, Naim wouldn’t sell themselves short, and for the 140 at least, for which I’ve seen an independent review, it is not borne out in testi measurements.. However, I suspect the belief stems from what I have seen in Naim specs regarding their peak (transient) power capacity, typically around 5x the rated RMS power - whereas the majority of other amps whose specs I have seen typically maximum peak is just double RMS. So the maximum transient power from a 250, at 400W into 8Ω, is much the same as that of many other amps with an RMS rating of 200W - 2½ times the RMS power of the 250. And, significantly, for music with a good dynamic range peak power is likely to be the limiting factor, with RMS limit not reached (different with heavily compressed music).

In other words, if my assessment is correct, Naim power amps actually are not more powerful than their specs - but they effectively are capable of more relative to the majority of other makes than the RMS power might suggest, relative to other amps. (Of course, if by ‘their specification’ you purely mean one part of their specification taken in isolation, namely RMS power output not all declared power power information, then your meaning is correct - and I suppose that in many instances that is all people consider - but specs are there to tell anyone wishing to know what an amp will do.

The 18.7 and 18.6 amp is the maximum Naim allow the output transistors to pass. Presumably when this figure is reached the amp will shut down, it’s a safety feature (for the transistors).

I’m no amplifier designer, but couln’t the increase in W with the same value of A, be down to an increase in V.

It's complex (literally, as in it's a function of complex arithmetic).  The difference as I said is how transients are reproduced.  Many amps try to deal with this by just increasing the RMS power.  But the RMS power of an amplifier is both measured and calculated for the steady state conditions when driving a simple sine wave into a fixed resistor.  This represents neither a real speaker, as:
Real speakers present complex impedances that vary with frequency (both the impedance and the phase angle vary with frequency)
Music isn't a set of steady state sine waves

Analysing and designing for wide frequency bandwidth at high power when reproducing steady state sine waves doesn't represent music very well, hence the power output specification on paper tells you nothing about the sound quality of an amplifier (unless you only listen to test tones rather than music!).

I know, in the past I've designed audio power amps (although admittedly my audio design work wasn't done commercially).

Huge posted:

Yes I do know what it is: it's the dynamic (i.e. transient) capabilities of the amp, 

Well, this isn't supported by the data:  The NAP250 RMS and transient power capabilities are tested as 92W and 93W, respectively while the NAP500 is tested as 144W and 142W, respectively - exactly what is expected with a regulated amp (with a "stiff" power supply).

Huge posted:

As Richard says - listen to them.

Well, that's not answering the question the OP was asking.

sktn77a posted:

Huge posted:

Yes I do know what it is: it's the dynamic (i.e. transient) capabilities of the amp, 

Well, this isn't supported by the data:  The NAP250 RMS and transient power capabilities are tested as 92W and 93W, respectively while the NAP500 is tested as 144W and 142W, respectively - exactly what is expected with a regulated amp (with a "stiff" power supply).

I wrote transient capabilities not transient power.

There's a lot more to amp design than power output.

Amongst other things, you need to start to understand how the the dynamics of feedback networks interact with the forward gain, the use of bypass capacitors and the pulse characteristics of different types of capacitors, to name but three.

(Actually when you truly understand it you'll realise that, for an audio amplifier, power output isn't a particularly significant measurement, static or transient.)

What are "transient capabilities"?  Please explain.

Look at the waveform of a sine wave, compare that to a real music signal; the one is predictable, the other essentially isn't.

Transient capabilities are those aspects of an amplifier that allow it to amplify and simultaneously reproduce large and small, unpredictable short term changes in the signal, accurately and faithfully, both in the amplitude domain and in the time domain.