The imperfect amp: Pass or Ayre?
Specs don’t mean crap, it’s all in what you hear and like. A lot of audiophiles feel that way. However as I see it specs (and measurements) can often provide a lot of value in two ways: 1) By allowing one to identify and RULE OUT from consideration candidates for purchase that would be poor matches to either the surrounding components or to the user’s requirements. An example of the latter would be how much power is needed to support desired peak volumes. Examples of the former would be incompatibilities due to impedance issues, gain and sensitivity mismatches, and various issues which can result in amplifier/speaker mismatches. One way in which specs and measurements can sometimes serve that purpose is by providing insight into the priorities of the designer, and in doing so making it possible to identify misplaced priorities. Such as specs that may be TOO good and thus may signify undesirable design tradeoffs. A classic example of the latter would be an amplifier having unusually good Total Harmonic Distortion numbers relative to other comparable kinds of designs, which can signify heavy-handed application of feedback in the design, with the downsides that have been mentioned. If specs are disregarded and/or are not properly understood the randomness of the process of assembling a satisfactory system, and the likelihood of expensive mistakes, are significantly increased IMO. 2) Specs and measurements are also often useful in troubleshooting problems and diagnosing sonic issues. I couldn’t begin to count the number of times I and many others have referred to John Atkinson’s measurements in Stereophile in addressing such issues in discussions here. @Nrenter, thank you kindly for the nice words. Regards, -- Al |
To add to @almarg 's comments above, specs *are* important; perhaps the one that can be the most counter-intuitive is THD, as a very low THD spec is often an amp that doesn't sound nearly as good as one with a higher THD spec. I've already explained why above. But bandwidth is real, output impedance is important (which isn't to say that the lowest output impedance is the best). Some speakers **require** that the amp have a higher output impedance, such as ESLs, horns and single-driver full range loudspeakers. Or any speaker where the designer has sorted out that he doesn't like brightness and harshness and so has designed the speaker for amps designed with intention to not have these properties (and often that means no feedback, so a higher output impedance). For more on this topic see:http://www.atma-sphere.com/Resources/Paradigms_in_Amplifier_Design.php Now I discovered back in the 1970s that feedback wasn't all it was cracked up to be; that it could cause the amp to have a smaller soundstage (unlike the original recording; I know that from the use of master tapes) and be brighter than the actual recording as well. Since then I learned there is far more to it than just that simple concept- the use of feedback introduces about 7 different variables that the designer has to weigh out. FWIW the feedback formula doesn't offer a lot of guidance in that regard: in a nutshell most amps with feedback have a rather cursory application and ignore some factors (like RFI leaking into the amp via the speaker cables) entirely. So of the specs that are suspect as to how much they contribute to good sound in an amplifier, IMO/IME the two top suspects appear to be THD and output impedance (IOW a better sounding amp might be one where these specs have higher rather than lower numbers). Alternatively we also know that IMD is highly audible so low IMD specs are a very good sign but IMD is more pervasive than most audiophiles like to think about. In addition to the normal interactions between two tones, IMD also is a major issue in digital audio, but because the intermodulations are having to do with the scan frequency and the Nyquist Theorem, its called 'aliasing'. But as far as the ear is concerned, aliasing (the digital industry does not like to refer to it as a distortion, but that's exactly what it is) is an intermodulation (sometimes called 'inharmonic distortion' in the analog world) and so highly audible (the ear treats it as a brightness or 'crispness' and its still there if you turn down the treble, because the brightness is caused by distortion rather than frequency response). Of course if you look at the specs of a digital product, this form of distortion isn't listed. Again- the Emperor's New Clothes. Fortunately the digital world has been getting a better handle on this in later years; the more they do so the more natural digital is able to sound. |
I think specs and measurements are for the most part stuck in the 1970s when it comes to amplifiers and electronics, despite better tools. Yes, we can measure THD 100x better and cheaper. But have we added any meaningful measurements? Anything new that helps describe a listener, room, speaker, amp interaction with a particular amp? A lot of what I think I'm circling around is bemoaning that we don't have better. While some speaker makers have gone to great lengths to connect measurements to listener preference, if amp makers are doing this, for the most part I haven't heard of them. Pass, to his credit, makes some of what he's trying to do transparent. It would be nice to me if I could go from my preferred amps to specs and go "aha! This is what I like!" and therefore, buy the cheapest that fits. :D :D :D |
