Absolute Sound

L E T T E R S
hearing with any “digital” system for
one all-overruling reason, which is the
fact that “any” digital system is locked
by a steady clock frequency, resulting
effectively in a steady “refresh” of the
presented information, independent of
frequency; whereas the hearing uses NO
clock and every “nerve” action is totally
individual, therefore we have many,
many random moments of reception,
and at one given moment in time our
hearing system is receiving and processing
multiple stimuli. This makes our
hearing essentially “continuous.”
Secondly, briefly regarding even/
odd/lower/higher order harmonics:
Omitted in this first discussion is the fact
that most distortions of solid-state gear
are lower than those of tube gear by a factor
of 100 or more. This difference must
be incorporated in the reasoning of the
influence of distortions on our perception
of musical information. Otherwise it will
be a hollow argument.
I myself would argue that two other
phenomena play the dominant role in the
differences between tubes and solid-state:
One is the fact that electrons (and
holes) travel 10 times faster in a vacuum
than in doped silicon, and it takes
another order of magnitude of time for
the electrons to get moving in the first
place (avalanche effect; at least in bipolar
transistors, FETs are faster), which
adds up to a difference in propagation
delay of 100. Tube amps therefore have
100 times (not really because of the
transformers but for the sake of the
argument) higher transition speed and
hence a 100 times lower negative influence
of the always-too-late negative
feedback. In my view this is the single
most dominant factor of detail-masking
in solid-state amplifiers. Feedback that
is too late is in fact truncating low-level
information instead of reducing
“dynamic” distortion products. In tube
amps this feedback is thus 100 times
more effective, dynamically. So in fact
to reach “solid-state levels” of negative
“NFB artifacts,” you can apply 100
times more feedback in a tube amplifier.
When you do that I bet that they
don’t sound very different from each
other anymore.
Secondly I would say that the output
impedance in conjunction with NFB
also plays a major role here: tube amps
with damping factors of 8...80 do not do
a good job in eliminating ringing of the
moving mass (cone, motor, air) in loudspeaker
systems.
This is bad and good. Dynamic
loudspeakers have their most problematic
nonlinearities just around the center
position of the movement, i.e., in its
physical crossover region.
When a low/mid unit is still moving
somewhat after a bass burst, then lowlevel
information is more present because
it “rides” on the “ringing” of the loudspeaker.
So it is more audible, although
maybe a little bit distorted because of
mild IM—or Doppler effects, as it is not
“swallowed” by the problematic lowlevel
linearity of a cone unit. (This is why
E’stats and M’stats are far more revealing.)
However low-level detail also suffers
from the same mechanism because of
masking, when the cone is still recovering
from the bass pulse. But since the
concerned frequencies differ from each
other this will be a mild effect.
Hope this adds a little bit to the discussion,
which I find in fact an essential
one. You are literally raising fundamental
questions. This can only be done
properly in TAS.
Marcel Croese, Creato Audio
Hidden Factor in Tubed Sound?
Editor:
Your TAS Roundtable on “Tubes vs.
Solid-State” [Issue 147] was fascinating
and insightful. Several of the roundtable
members commented on the significant
differences in midrange reproduction
between solid-state and tubes. While the
members explored many facets of this
timeless question, one was overlooked. I
believe the quality of low- and high-frequency
reproduction has a profound effect
on our perception of midrange accuracy. I
submit that the midrange will sound different
in systems with identical midrange
10 THE ABSOLUTE SOUND ■ JUNE/JULY 2004