pmt (08/12/82)
I'm not sure exactly what you are calling "high end" equipment, but based
on the distortion figure you gave, it sounds like what Pioneer, Harmon-Kardon,
and the like are coming out with as the top of their line; i.e. claiming
incredibly low distortion levels. In regards to these distortion levels, it
is true that .00001 percent distortion is not going to sound any better than
.001 percent distortion. However, the former amplifier may sound better than
the later! This is because the distortion figures that the companies give do
not begin to tell the whole story. There are a multitude of distortions
inherent in audio equipment, many of which only show up in reproducing comp-
licated waveforms, not nice clean sine and square waves. For example, when
transistor amplifiers first came on the market, large amounts of gain were
suddenly available, which allowed the manufacturers to use incredible amounts
of negative feedback. Negative feedback is the process of feeding the output
of a stage (or stages) of an amplifier back to the input 180 degrees out of
phase. This effectively cancels out most of the signal, and has many advan-
tages: Most types of distortion (especially InterModulation) are SIGNIFIGANTLY
reduced, the loading of the stage on the previous is reduced, and the capability
of the stage to drive low impedance loads is increased. However, many people
did not like the "sound" of the new amplifiers, and it became obvious that
some type of distortion must exist at rather high levels (10%?) that was not
being measured. Several years ago, a new type indeed was measured, named
TIM (Transient intermodulation distortion) It was found that on large tran-
sients (like a drum beat) the signal would propagate through the stage with
such an abrupt change that the negative feedback simply could not get back to
the input and cancel it out in time; thus the transient was magnified many
(perhaps thousands!) of times from what it should have been. Design of better
feedback systems as well as using less negative feedback has improved this
problem considerably, to the point where I believe the best solid-state amps
are better sounding than the best tube amps. (Although there are people who
will differ with these views!) Nevertheless, I must emphasize that by no means
are manufaturers accurately describing how a piece of equipment will sound by
their specifications - I suspect that the price would be equally accurate!
There are companies which manufauture "true" (at least in my opinion)
high-end gear. These companies do not put much emphasis on distortion
specifications; they know that people interested in their equipment will
let thier ears decide what is best. A few companies with such equipment
are Threshold, Mark Levenson, Sun, Planar, Hafler, etc. etc.
This grade of equipment sometimes is no more expensive than the
"name brand" stuff, and the difference is noticeable. I would suggest
that anyone interested in getting a nice system look into the non-
name-brand stuff; better audio stores carry quite a large variety of equipment.
I don't claim to be an expert on stereo, but I have learned quite a bit since
I bought my first Pioneer SX-1250 couple-hundred watt reciever, and shortly
gave it up in favor of some Dynaco tube amplifiers... If anyone is interested
in my opinions about anything, I'd be happy to ramble for hours! In the mean
time, this article is getting rather long.......
Paul M. Thompson
Electrical Engineering Senior
University of Minnesota