XPA-2 or two XPA 100

[garbulky]

Fwiw b-stock is slightly different from used gear on the forum.

[bootman]

Jun 29, 2013 3:12:12 GMT -5 audiosanity said:

...the XPA-100s each have a measly 360VA transformer. The XPA-2 packs a 1,200 VA monster. The only thing going for the monoblocks is the cool/bragging factor.

So I take it you also don't like class D designs with no transformers?

The transformer alone does not a power supply make.
Please do some research before spreading FUD like that.

The current line of Emotiva amps run off the secondary capacitance which in turn is fed by the transformer.
The design is fully capable of outputting the rated watts.
It is also a more power efficient design. (from a running cost point of view)

[audiosanity]

Jul 2, 2013 22:03:13 GMT -5 bootman said:

Jun 29, 2013 3:12:12 GMT -5 audiosanity said:

...the XPA-100s each have a measly 360VA transformer. The XPA-2 packs a 1,200 VA monster. The only thing going for the monoblocks is the cool/bragging factor.

So I take it you also don't like class D designs with no transformers?

The transformer alone does not a power supply make.
Please do some research before spreading FUD like that.

The current line of Emotiva amps run off the secondary capacitance which in turn is fed by the transformer.
The design is fully capable of outputting the rated watts.
It is also a more power efficient design. (from a running cost point of view)

Don't all A/B amps "run off" the capacitors, which are fed by the transformer? Which line of Emotiva amps has not done that? Why are we even talking about class D amps?

One reasonable way to compare the amps is to look at the ratio of the capacitor energy to transformer size. The XPA-2 has an "effective capacitance" rating of 45,000uf, however, the energy stored is proportional to the 180,000uf of capacitor banks. The XPA-100 has 60,000uf of capacitors.

- XPA-2: 180,000uf / 1,200VA = 150
- XPA-100: 60,000uf / 360VA = 167

So these ratios are quite similar.

We then look at output watts over transformer rating:

XPA-2: 600W(2 chan) / 1,200VA = 0.5
XPA-100: 250W / 360VA = 0.69

Now that is a significant difference. It means the XPA-2 should have been able to pump out 2x300W with only a 864VA transformer. So we have to ask ourselves what is going on here? Did the ability to put out so much power result in some compromises in efficiency? Or does the XPA-2 have some capabilities not reflected in the specs, such as higher headroom, significantly higher peak current ability, etc.? Your answer seems to be that the XPA-100 is simply a far more efficient design. But the implication is that the XPA-2 is a horrible design from the point of view of efficiency. But audio amp design is not rocket science, and I can't imagine such a huge disparity in efficiency.

So there must be a simpler answer. And I think this is it:

The power ratings we get are essentially rounded off numbers, or they are obtained differently. The first thing that jumped at me is that the XPA-2 is rated at 0.1%THD, while the XPA-100 is rated at 1%THD. Fortunately, Emotiva makes measurement data available, and when you look at page 6 for the 8 ohm measurements of the XPA-100, it is obvious that at 0.1%THD, the XPA-100 produces about 200W. So for the XPA-100 to be scaled up to the XPA-2 level, it would need a 2*360*(300/200) = 1080VA transformer. That's not far from the XPA-2's 1,200VA. Now if the XPA-2 is slightly underrated at 8ohms, say it can really output 310-320wpc at 0.1%THD, then, they are even more similar.

[audiosanity]

So the bottom line is that at 0.1%THD, the XPA-100 is really just a 200Watt amp, while the XPA-2 is 300wpc. So there is no efficiency magic going on. Power output and transformer size do scale similarly for the XPA-2 and XPA-100. It's just that the XPA-2 is indeed a more powerful amp. So you can use your money for two chassis or 50% more power.

[deltadube]

get some XPA 1s and dont worry about it!

cheers