
There are, today,
many solid-state power amplifiers that are highly accurate. They replicate the
input signal with extremely low error, so it’s virtually impossible to separate
such amplifiers by merely listening; they’ll simply sound identical.
Distinguishing differences generally involve power output capability, load impedance
compatibility, basic circuit design (and choice of active components), intended
reliability, and target market. One needs to push deeper into the technical
detail to make sensible decisions about benefit-versus-cost aspects; listening
isn’t enough.
Given this state of
modern amplifier excellence, it’s unrealistic to expect equivalent accuracy
from vacuum tube dependent design. The archaic limitations of the triode tube
(Lee DeForest, 1906) are not consistent with contemporary medians. Ruler-flat
power response, near-zero (< 0.1%)
total harmonic distortion (THD) at full rated power, and ultra-low output
impedance (~ 1/10th the Zout of a typical tube amp) is now routine in the case
of most solid-state power amplifiers. Identical measurements made on the very
best vacuum tube models show that they can’t approach the same readouts. For
example, consider THD: Typical “high-end” tube-type audio power amplifier THD
limits are ~ 16X to 50X worse than as specified for a popular “mid-market”
solid-state power amplifier.* (They’re 1% to 3% THD instead of 0.06% max.) That’s
undeniable regression. Of course, tube boosters assert that this shortcoming is
actually beneficial. They claim that vacuum tube amps will thereby render a
warmer, more euphonic (?) sound. Given this Zen-infused perception, tube power
amplifiers can seemingly transcend their intended role and become creative (but
arbitrary) signal processors. This uncontrolled mutation is not consistent with
the initial (accuracy) objective.

Apply that “euphonic
polishing” later, at the loudspeaker stage. The speakers’ performance will be
inseparably linked to the acoustic characteristics of your listening room, so
it’s sensible to address both of those issues together—without the need to
compensate for anomalous amplifier sound.
*Parasound’s Halo
A23+ power amplifier ($1,495 list) versus the best from PrimaLuna, VTL, and
VAC.
BG (February 2019)
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