The
transistor has been around for 50 years now (as of 1997), and solid state
technology must be considered mature. Further developments are
likely to be evolutionary in nature, such as size reduction, rather than
revolutionary. This is just the nature of innovation, a point of
diminishing returns for a given technology. Radically new ideas for
solid state amplifier circuits are unlikely.
The
triode vacuum tube has been around for 90 years and the beam power tube
for 61 years. So, vacuum tube technology and circuit design is
also quite mature. Further major developments are unlikely. In
fact, the improvement of modern vacuum tube amplifier performance over
units from the 1950's is due primarily to changes in other components,
such as capacitors and resistors, and attention to detail.
So, today when we compare a solid state audio
amplifier with one using vacuum tubes we are observing a showdown between
two very mature technologies. All of the improvements in auxiliary
parts are available in both types of amplifiers. And, lo and behold,
the vacuum tube still produces superior sonic performance.
What
accounts for the tube's ability to survive and dominate the modern high
end audio world? Many would say that it is because the tube produces
a pleasant distortion. However this is just not the case. A
well designed tube amplifier can produce vanishingly low levels of
measured distortion (.01% and less is easily obtainable in preamplifiers)
and extremely wide frequency response. The small amount of
distortion produced in a tube circuit is mostly second harmonic, which is
the type most easily disregarded by the ear.
For those who feel that the transistor represents
better objective science, consider this. Both the tube and the
transistor have parameters known as stray capacitance. That is, just
by physically existing there is unwanted capacitive coupling between
various elements of the devices (ex: plate to grid, collector to base).
These can not be avoided. In essence there are several small
capacitors contained in each tube or transistor.
In the vacuum tube the dielectric for the stray
capacitances is nothing, a vacuum. This is the finest dielectric
known, having far and away the lowest losses and least dielectric
absorption (the way in which capacitors color the sound by reradiating
stored energy).
In the transistor the dielectric is silicon,
germanium, etc. In other words, using each transistor is essentially
as bad as sprinkling a few ceramic capacitors in the circuit. Given
a choice, no audiophile would allow even polyester caps in the audio
signal path, let alone ceramics. Add to this the fact that
transistor design typically uses 200% to 500% more active devices than
tube circuits do and it becomes readily apparent why transistor amplifiers
display strange subjective characteristics, particularly at mid and high
frequencies.
There are many other technical ways in which the tube
is scientifically superior to the transistor. They are sonically
superior as well.
Isn't it time you listened to tubes?