In this small article for the Sound Advocate, I offer a summary of the role of power amplifiers today: tubes vs. solid state designs. (* see below)

As most audio enthusiasts know, there are a plethora of many well-designed solid-state power amplifiers that are highly accurate and wonderfully satisfying when mated with the proper loudspeakers. They replicate the input signal with extremely low error, and I have found, in many double-blind listening tests, nearly impossible to separate them.

The Parasound A23 solid state amplifier
Parasound A23 amplifier

Their most notable design differences are often related to power output capability, load impedance compatibility, and intended reliability (MTBF) so, one needs to push deeper into an examination of the technical side to properly decide on benefit-versus-cost concerns. Listening may not be enough.

In fact, the power amplifier needs to accurately amplify the input signal, and transfer that signal, fully intact, to a low impedance load. A well-designed power amplifier, in theory, is not supposed to reshape the input in any unintended or involuntary manner, so I support the concept that accuracy improves when the potential for error and distortion is minimized.

Given the current state of amplifier excellence, it is my firm opinion that it is unrealistic to expect equivalent accuracy from most vacuum tube designs. The archaic limitations of vacuum tube circuitry, in most circumstances, are just not consistent with modern quality medians.

Ruler-flat frequency response, near-zero (< 0.1%) total harmonic distortion (THD) at full rated power, and ultra-low impedance output coupling is now common with many of the finest solid-state power amps. However, similarly related measurements made on the very best vacuum tube models show that they cannot approach the same results.

For example, many of the current “high-end” tube amplifiers THD limits are ~ 16X to 50X worse than as specified for a popular “mid-market” solid-state power amp* (1% to 3% THD instead of 0.06% max.). Most people would agree that this is serious regression.

Mastersound evolution 845 tube amplifier
mastersound evolution 845

Tube amplifier ‘devotees’ assert that this shortcoming is actually beneficial, and that vacuum tube circuits thereby render warmer, more euphonic, more satisfying sound. In many instances, with certain loudspeaker designs, this may well be true! However, given this Zen-infused perception, tube power amplifiers seemingly transcend their assigned role and become creative (but arbitrary) signal processors—which is precisely not the kind of amp that I personally can trust.

I prefer performance that’s pure, accurate, and error free, with some +2 or +3 dB more unclipped power than my speakers are rated to handle, as well as a good probability of long MTBF.  I’ll do my own “euphonic polishing” later, when I address my loudspeaker stage, which is where that subtle nuance belongs anyway

Comments and opinions are always welcome; after all, these are the areas where enthusiasts opinions on sound reproduction and technology in the world of high-end audio reproduction always cross!

*E.g. Parasound’s Halo A23 ($995 new) versus the best from PrimaLuna, VTL, & VAC.

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