Tab Electronics Guide to Understanding Electricity ... - Sciences Club

236 Chapter Eight
(same beta value, base-emitter forward voltage drop, voltage ratings,
etc.). Generally speaking, most audiophiles consider this to be the best
type of output driver design. Transistor manufacturers offer a large
variety of matched pair, or complementary pair, transistor sets designed
for this purpose.
Another common type of output design is called the quasi-complementary
symmetry configuration. It requires a complementary symmetry
“predriver” set, but the actual output transistors are of the same type
(either both NPN, or both PNP; NPN outputs are vastly more popular).
This type of output design used to be a lot more popular than it is now.
The current availability of a large variety of high-power, high-quality
complementary transistor pairs has overshadowed this older design.
However, it produces good-quality sound with only slightly higher-distortion
characteristics than complementary symmetry.
Audio Amplifier Definitions
The field of audio electronics is an entertainment-oriented field. The
close association between audio systems and the arts has led to a kind of
semiartistic aura surrounding the electronic and electromechanical systems
themselves. As with any artform, personal preference and taste play
a major role. This is the reason why there are so many disputes among
audiophiles regarding amplifier and speaker design. My advice is to simply
accept what sounds good to you, without falling prey to current
trends and fads.
Unfortunately, there have been many scams and sly stigmas perpetrated
by unethical, get-rich-quick manufacturers over the years. This has
led to much misunderstanding and confusion regarding the various
terms used to define audio amplifier performance.
The most heavily abused characteristic of amplifier performance is
“power.” Power, of course, is measured in watts. The only standardized
method of designating AC wattage, for comparison purposes, is by using
the rms value. Any other method of rating an amplifier’s power output
should be subject to suspicion.
Output power is also rated according to the speaker load. For example,
an amplifier specification might rate the output power as being 120
watts rms into a 4-ohm load, and 80 watts rms into an 8-ohm load. You
might expect the power output to double when going from an 8-ohm
load to a 4-ohm load, but there are certain physical reasons why this will
not happen. However, when comparing amplifiers, be sure to compare