“Longtime readers of The Audio Critic know the drill that comes at this point: I repeat, for the nth time, that all amplifiers having high input impedance, low output impedance, flat frequency response, low distortion, and low noise floor sound exactly the same when operated at matched levels and not clipped. (Those who are unable to stomach this simple truth, proved over and over again in double-blind listening tests, should stick with Stereophile.)”
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Tube amplifiers with their typical output impedance of >1 ohm will act as tone controls as they interact with the typical varying impedance of most speakers. Ohm’s Law applies here! Go look it up!
These two statements purvey the idea that its all about frequency response and low distortion. This promotes a falsehood, since frequency response is not the most important issue (meaning that low output impedance isn’t either).
Its all about distortion.
Less expensive amplifiers tend to be designed to look good on paper- i.e to have ’good specs’. More expensive amplifiers are often designed by engineers that understand that the audio industry hasn’t progressed much in the last 50 years as far as spec sheets go, and so look to advances in our understanding of human physiology that have been made in the last 50 years instead.
For example, the human ear/brain system uses higher ordered harmonics in order to sense sound pressure. This is easy to prove with very simple test equipment and this fact has been known for decades, but the spec sheets and what we think of as ’good specs’ still ignore this simple fact!
But many high end designers, including Nelson Pass and John Curl (both giants in the high end designer pantheon) understand that designing the equipment to not make certain types of distortion to which the ear is keenly sensitive will result in a better sounding amplifier, even if other types of distortion (to which the ear isn’t very sensitive at all) are present in higher quantities. It is this fact that is why tubes are still commonplace in high end audio.
A further fact about how the ear/brain system perceives sound is that all forms of distortion are converted into some form of tonality. The 2nd harmonic contributes to ’warmth’; the 7th harmonic (in much lower quantities!!) contributes to a harsh metallic quality. Both are colorations, and the ear has tipping points where these colorations predominate over frequency response; IOW you can have flat frequency response yet the system won’t sound flat at all due to the kind of distortion the amp makes.
The above quoted statements don’t take this into account.
What is needed is a weighting system, so that the distortions that the ear cares about are given more weight than those it does not. Spec sheets would look a lot different if that were the case!
Anyway, a well-designed amp that sounds good to the ears probably won’t have "good" distortion specs as it will likely have more lower ordered harmonics, but it will **sound** better and **more neutral**, if the designer was careful in the design. You won’t see that in cheaper gear- its all designed to look good on paper.
So yes, there can be an appreciable difference between high end and mid-fi gear.
