Power supply VA rating and how much is really needed

In theory at least, the sound quality doesn’t degrade until you reach the limits of the amp.

Are you going to run into those limits? :)

I mean, the argument can be made that overkill is the best kind of kill when it comes to engineering, but there is more to the sound quality than merely capacity. Noise filtering, storage capacity, decoupling and signal routing of the power supply matter a great deal as well.
It’s not really a spec that a lot of people should use. Fortunately the one thing that’s pretty well defined in terms of measurements are how you rate an amplifier, which is in steady state after a warmup at 1/3rd power. So assuming an amp meets its specs it will deliver as promised and leave the details of the power supply to the engineers.
It is important to note the power, impedance and number of channels driven at that specification.

Again, not sure overkill is something you can hear. A well designed small amp that is never used outside of it’s design envelope could sound fantastic.

But... let’s say you have some troublesome speakers like an ESL, or one that dips to 2-3 ohms in the bass. That will require more current. An amplifier needs to have 3 things to not wilt on a difficult speaker:

1 - Adequate power supply (VA) for the output desired
2 - Appropriate driver and output stages
3 - Low output impedance.
So, imagine a perfect amplifier with no output impedance and a limitless power supply. No matter the speaker, the Voltage will not change.

On the other end are high output impedance amps. Typically tubes. Their output is a little dependent on the speaker’s impedance itself.
You can see this in Stereophile review of tube amps with the simulated speaker load.

Is that bad? Well, it’s not precise, but you might like how it sounds.

Best,
E

Kind of on this theme, Nelson Pass has written a great deal about how we test, measure and evaluate amps. He makes the convincing argument that the 1st watt is the most important one.

What the distortion or noise is at 250W is irrelevant because no one uses it. You want an amp that is low noise, low distortion and performs beautifully in the first few watts, and has power to not compress.

And one thing I find VERY true is that a lot of amp makers rate the S/N at full output. It tells you nothing about the relative noise. The most careful makers rate Signal to noise at 1 watt. That tells you whether a 50 W amp is noisier than a 500 W amp much more reliably.

@erik_squires 

Thanks I will read up on what Nelson Pass has written.

Based on what you have stated. And your knowledge base - 

given a budget of approx max $2k-$3k... 

all things being equal ... which do you think is a better amp based on specs? And which do you think would be a good fit for B&W speakers?

monoprice 1800/2007 ati clone?
odyssey stratos 2 or 3 ch or khartago version
rotel rmb-1585
emotiva xpa5 
outlaw 7700



I realize that how things sound is the end game -- and these are not top tier products - as they are all midfi at best... but I don't have the budget for the likes of Pass, Levinson, etc... 

Am I missing any contenders in the amplifier space that I should consider?


 

Used, ATI and NAD's multichannel amps with Hypex class D stages.

Otherwise Rotel.

I have not heard Outlaw and Emotiva amps, but I have tried the top of the line, mail order HT processors and they were crap. I mean, worked well, looked fine, sounded like crap. Really really thin, gutless. No noise, but also no depth or credibility so I have never gone back that route. 

Sorry, I've been on somewhat of a hiatas from some frustrating audio testing and then thanksgiving and then getting sick. 


Generally speaking, I would not pay too much attention to how many amps output.  The specifications that say "40A output" are pretty meaningless.  The "output watts" is a specification that will indicate the overall size of the power supply.  A 500 watt monoblock amp is going to have a rather large transformer and a large power supply capacitor bank.  Obviously, you are not going to use all 500 watts for a single speaker, but the benefit is going to be much smoother sound, fuller midrange, and much stronger and fuller bass.  It also depends on how hard your speakers are to drive.  A smaller 150 watt amp would probably be fine on a more efficient high impedance speaker - such as a flat 8 ohm speaker that is 91db efficient.  Once you start going down in impedance and efficiency, you really want a beefier power supply - which translates to a larger power amp.

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Another part is the sonic signature - do you want a very fast responding "Class B" type of amp, or do you want a very warm sounding "Class A" type - or something "neutral" in the middle.  It all comes down to personal taste.  I just finished my own evaluation of different amps and have heard a whole lot of different electronics when I went to RMAF.  In my testing, I would say that the Parasound was the best in fullness and natural sound, but it was too warm for my tastes.  Bryston cubed amps were very nice and very high resolution, but were too thin/fast for me (they are just about the closest to a Class B amp you can get).  The Classe Audio monoblocks I tested sounded very clinical and sterile in my system, but they did have good resolution. 

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So, in my frustration, I just went back to Emotiva and purchased a pair of their 2-channel fully differential amps (the XPA-DR2 models).  I have one amp powering the front left / surround left.  And the second powering the front right / surround right.  Obviously, I'm balancing the power supplies in the amps so that they are used most efficiently, but at a rating of 550 watts per channel, it is totally fine.  I will say that after hearing gobs of ultra expensive electronics and a variety of different sonic signature, the new Emotiva differential amps are PRETTY DAMN GOOD!  I originally had Emotiva XPR-1 amps (1000 watt monoblocks) for my left/right which I sold earlier this year and regret that.  The new amps are only 4 days old and still burning in so I won't have a final judgment for another week or so.  It's very difficult to tell if these are going to be better than my original XPR-1 amps or not.  I will say my system sounds the best with Emotiva monoblocks (whether they are the old XPR-1 or the new XPA-DR2).  The Emotiva are very neutral amps, but they have excellent resolution.  The sounds/vocals are very realistic and they are extremely engaging with my B&W D3 speakers (which none of the other amps really gave me).  At this point, the amps do not quite have the amount of bass/midbass that I would like, but they are still burning in.  They are a slightly different amp board and the power supply is the switching power supply instead of a massive transformer and capacitor bank.  That may translate into how much bass strength I have.  I will know more in about 4-5 days.