It's not that there's no possible way; there are infinite ways to screw things up. It's that if they're well designed to do a particular function, then you should consider that it's likely they would actually do that function.
CAN two different but
well-designed power amps sound different? The knowledgeable and respected EE's seem to always say "No!" Many musicians say "Yes!" I'd like to approach this question in a
completely different way. It may turn out that both can be right. (What??
) Here are the assumptions I'm proceeding with for comparing the two amps:
1. The amps being compared are being tested
within their linear region, and
within their headroom.
2. Frequency response is reasonably flat within the audible range, say +/- 0.1dB 20 - 20K Hz.
3. THD is reasonably low; say 0.1% into the same nominal load, i.e., 4 ohms, at the same wattage.
4. The ear is not able to discern distortion or change of sound at 0.1% THD.
At this point it appears as though Brand A and Brand B
should sound identical. I'm sure the EE's would say they will...
But there may be one
very important aspect that has not been considered when comparing the sound of two power amps: that of the effects of a reactive load presented to the amps in real world conditions. (Hold on EE's, don't start getting steamed up - YET! "Wait - there's more!"
) Let's now say we're talking about the load presented by a real, reactive 4 ohm speaker. We know that the nominal impedance is 4 ohms, but the actual impedance is frequency dependent. "Frequency dependent." That's key in my hypothesis. While amp Brand A and B are putting out the same wattage at 4 ohms, they are NOT putting out that wattage as the impedance changes with regard to frequency, due to the impedance curve of the speaker. Because of the speaker's reactive nature, as the impedance drops at one frequency, the speaker draws more power; as the impedance rises at another frequency, the speaker draws less power. This results in a change in SPL inversely proportional to load impedance. OK, so far, so good - everyone already knows this too.
But here's the problem: THD and frequency response measurements are generally done with a sine wave into a nominal non-reactive load! But a single bass guitar note consists of
several frequencies simultaneously: its fundamental frequency and its harmonic frequencies. "Tone" itself is defined as the relative proportion of the amplitude (or, in real world conditions, "SPL") of the fundamental frequency to the amplitude (SPL) of its harmonic overtones. For example, a low E on the bass consists of a fundamental of 41.2Hz, with overtones of 82.4Hz, 123.6Hz, 164.8Hz, 206Hz, 247.2Hz, 329.6Hz, etc. Now here's the "ohm my god" question:
What would be the result if Brand A and Brand B amps both put out the same power at exactly 8 ohms, BUT DID NOT PUT OUT EXACTLY THE SAME POWER AS EACH OTHER AT THE SUB-NOMINAL OR HYPER-NOMINAL IMPEDANCES PRESENTED BY THE REACTIVE SPEAKER? The answer seems simple to me: the
actual SPL of certain frequencies would be
different in the two amps! This would result in a
change in TONE since tone is completely dependent upon the relative strength (SPL) of the harmonics to the fundamental! It is well known that the power put out by two different amps at 8 ohms will not have an identical 4 ohm rating. Depending on design or efficiency, the 4 ohm rating of one amp might be 45% greater than that of its 8 ohm rating, whereas the 4 ohm rating of another amp might be 90% greater than its 8 ohm rating. We also know that some amps rated down to 4 ohms have more trouble putting out power at sub-nominal impedances. Therefore, I'm suggesting that unless each of two different amps puts out exactly the same power at a given load impedance, it doesn't seem possible that they could sound absolutely identical when presented with
simultaneous multi-frequency content such as that coming from a bass guitar note with its fundamental and various overtones!
Obviously if the speaker had a constant, non-reactive impedance both amps would sound identical. But it doesn't! IMO, you can talk about the specs or response of a given amplifier academically forever, but you can't actually talk about it's "sound" without it being a function of the reactive speaker load it's driving. Of course, the real question is whether this difference IS actually audible, or how much so. But enough people here have posted their opinions of how they hear different (excellent) power amps sounding different to make me really wonder. EE's, hit me with your best shot on this idea of mine. If I've missed something or am totally off the mark with all of this, I'd rather be set straight than suggest and pass along any misinformation like the one about clipping destroying speakers.
) responsible for why some people are hearing differences between power amps. I'm not an EE, so I need someone mightier than me in this field to answer this. I'm only hopefully smart enough to merely ask the question. 
