I'm going to chime in with the objectivist point of view here. (And, just to avoid any complaints, I'll say up front that I haven't heard any of the AudioSource amps, although I have heard of the brand.)
As an objectivist, I'll start by saying that it seems pretty obvious that, if the two amps sound different, then there must be an actual difference.... so one must make more distortion, or more noise, or perhaps a different
type of distortion, than the other. Now, from personal experience, I know that the XPA-1 is a pretty neutral sounding amp, and the differences between neutral sounding amps should be pretty small (if audible at all) since, while there are an unlimited possible types of coloration, there is only one neutral. Just like you can make glass in a virtually unlimited number of colors, but there is only one "clear". (In other words, if the two amps sound very different, then at least one of them must be wrong.... although, of course, we must include the possibility than an error in one component may cancel out an error in another component, and give you a more correct
overall result in a particular system.)
Considering that this is an amp with much lower power, and the description of the difference, I do have a theory - which I have seen occur with other low-powered amps (and especially with tube amps).
The XPA-1 has a distortion characteristic which is typical of a modern high-end solid state amplifier; the amount of THD it produces is very low (inaudible to most people, including me) until it reaches its clipping point, at which point it rises quite suddenly. Once you do drive the XPA-1 loudly enough to cause it to clip a significant percentage of the time, it will start sounding bad, but the whole point is that you should have plenty of power to avoid ever reaching that point, so you should always be listening to it operating cleanly.
In contrast, if you use a lower-powered amplifier, you will be more likely to cause it to clip. (In the case of the AudioSource, it also has an optional Peak Limiter - which is a nice way of saying that it compresses the peaks, which prevents it from hard clipping at very loud levels, at the cost of introducing more subtle soft clipping - distortion and alteration of dynamic range - at lower levels.) Considering the difference in overall power, I wouldn't be at all surprised if measurements showed that you
ARE running the AudioSource close enough to its power limit that it is clipping occasionally, or that it's Peak Limiters are "engaging" (if you left them turned on).
So, how could distortion make an amplifier sound "better"?
Well, our human brains are wired to interpret distortion as increased volume (that's why a 1 watt table radio can sound louder than an XPA-1 if you turn it up high enough; it will sound
nasty but it will also sound
louder than it really is).
Let's assume we have two amplifiers:
1) A clean, powerful amplifier that can produce 10 watts at 0.01% THD, and can also produce 100 watts at 0.01% THD.
2) A less powerful amplifier that can produce 10 watts at 0.01% THD, but that can only deliver 100 watts at 10.0% THD.
As long as we play both of those amplifiers quietly (let's say 1 watt average and 10 watts on the peaks) they should sound the same. But what if we play both a little louder (let's say we now run them both at 10 watts average and 100 watts peak)? What's going to happen then is that both will be playing cleanly most of the time, but the weaker amplifier will be producing distortion on the peaks... and this distortion will make the peaks
sound louder on the weaker amplifier. So, if you think about this for a minute, the quiet spots in the music will sound the same loudness on both, but the louder parts of the music will sound "more louder" on the lower powered amp that is making more distortion (because the higher level of distortion will make them seem louder). This means that, on the weaker amp,
the apparent difference in perceived loudness between the quite spots and the loud spots will seem greater.... which is another way of saying that, when played on the weaker, the music will
SOUND LIKE it has more dynamic range. The situation is a bit more complicated because we also find most forms of distortion quite unpleasant in large amounts, so there's a "tradeoff" point where a little extra distortion, and distortion of certain types, can make the amp sound "more dynamic", but too much extra distortion just sounds "loud and nasty".
This is a huge factor with certain specific types of amps - especially "single ended triode" tube amps - which have very high levels of distortion which increase linearly as you increase the power (rather than suddenly). Because many people don't find the second harmonic distortion they produce to be especially annoying as such, their linearly increasing distortion (referred to as a "monotonic distortion curve"), makes then seem more "dynamic" (because it exaggerates the difference in perceived loudness between the quiet and loud spots in the music - just like a dynamic range expander does), and "more powerful than their power rating would indicate" (because the increasing distortion makes them sound louder when you turn them up). However, it can occur with other types of amps as well.... (the key is in having the amplifier produce
enough distortion to make the loud parts of the music sound louder without producing enough distortion to make them sound noticeably bad).
(If you've been playing that AudioSource amp with the Peak Limiter enabled, then this is almost certainly what's happening; and it will be easy enough to tell that by turning it off. if it happens even with the peak limiter off, then I would suspect it was simply due to the lower-powered amp distorting a little bit during peaks, which makes the peaks sound louder. Either way it's something that would be easy enough to see with an oscilloscope or an AP. Honestly, if you're dealing with an amplifier of limited power, it may not a bad compromise, but I'm pretty sure the XPA-1 sounds more accurate, which, as an objectivist, is my goal.)
I'm the owner of XPA1 mono blocks 1st gen. and have be satisfied with them until I ran an experiment and hooked up one of my cheapest amps, an Audiosource Model Amp 2 and low and behold, real music. I thought all this time my speakers were a problem but not to the extent that I was completely dissatisfied but not completely satisfied either. I thought the Audiosource wouldn't have enough power to drive my B&W 802N's so I put off trying it for a long time. Now I here the instrument, air or space around the instruments, just more natural sound. I'm not complaining but I am suprised. I do know the XPA1's have a great deal more power and can drive my speakers more efficiently at higher volumes but something is missing, the music is just not alive as with the Audiosource. Why does this $100.00 amp sound so much better than my XPA1's ?
I try not to beat around the bush. So there are at least two to three reasons why the audiosource sounded better.
The first and probably the least satisfying choice is....the audiosource is a better amp. Just a darn good amp
The other choices are:
- In my experience, electronics sound different from each other and the speakers need to be fine tuned in terms of placement and ESPECIALLY toe in to get it just right. So for instance, the audiosource may just have gelled really well with your speaker placement. Also some older amps have bass boosts or a loudness boost sometimes incorporated as a button which can give a nice punchy presentation basically for quieter volumes
- Most likely, I think the problem may be your pre-amplifier. The big emotiva power amps - according to my *personal (subjective) experience (see below)* simply do much better with a
quality dedicated pre-amplifier. Without it, the sound tends to be weak-ish and the soundstage not quite as encompassing, solid and "real". This may be what your XPA-1's are missing. If you feel like it....audition an XSP-1 with your emo amps and see if it makes a difference. What is your source (and pre-amp) by the way?
*"Subjective": To be sure to stay fair and balanced. The cons of subjective impression go like this....
- "The sky is really blue today"
- "How in the heck can say that? Did you even compare that with another sky side by side with your eyes closed? I didn't think so.
- "No I mean the sky above is this beautiful vibrant shade of blue that warms the cockles of my heart."
- "And what color temperature is this blue sky in Kelvin please? Bet you don't even know what the heck that is do you? Bah humbug on your "blue" sky!
Summary: subjective impressions are subjective!
Pictured below: The correct way to look at a blue sky.