I should note that this discussion is about consumer grade home=20
entertainment amplifiers. Public address and musical instrument =
amplifiers=20
require much higher power levels and must have the capability to =
sustain=20
high output levels for long periods of time without being dammaged. =
In=20
short, they are a horse of a different color.=20
The question of how much power is enough is one that can be =
kicked back=20
and forth and never really solved. Perhaps a little history might =
be of=20
help. =20
Some of the first amplifiers that called themselves high fidelity =
used=20
6V6s, 6L6s, or other comparable tubes that delivered 10 to 25 watts. =
This=20
was before the popularity of stereo so the qualifier "per channel" =
is=20
unnecessary. When tube technology was at its pinnacle, stereo was =
becoming =20
quite popular, and transistors were just beginning to be heard from, =
The=20
amplifier many audiophiles aspired to was a 50 watt per channel =
using EL34s.=20
=20
Most equipment reviewers agreed, at the time, that the Heathkit =
AR-15 was=20
the breakthrough product for solid state amplifiers/receivers. For =
those=20
too young to remember and who think of the AR-15 as a gun, The =
AR-15, and=20
later the integrated amplifier version AA-15, gave 50 watts per =
channel and=20
previously unheard of low distortion figures. =20
The sound seemed good but something sent the serious listener in =
search=20
of higher and higher power levels. That something was transient =
distortion.=20
It can't be measured and quantified in the laboratory so the only =
way to=20
test for it is to listen. Listening tests are so subjective that =
you would=20
be hard put to find two people who can arrive at the same conclusion =
about a=20
given amplifier.=20
In the section titled "Overall Feedback, Pros and Cons" I =
describe in=20
detail what is wrong with solid state amplifiers. A brief summary =
is that=20
the solid state amplifiers used too much feedback. The attitude of =
most=20
design engineers is "if it can be done, let's do it." The =
elimination of=20
the output transformer with its large inductance and magnetic =
non-linearity=20
opened up the possibility of almost limitless amounts of negative =
feedback. =20
So, they pored it on. The result was very low steady state =
distortion=20
values but in listening test most agreed that the amplifier had a =
somewhat=20
harsh sound as if it were being driven very close to clipping. The=20
statement was often heard that "tubes overload more gracefully than=20
transistors." =20
Fans of tubes stayed with them while fans of transistors, myself =
included=20
in those years, sought higher power. For me it culminated in a =
200 watt=20
per channel amplifier of my own design. Its sound was effortless =
but I was=20
only using about 1% of its capability. Unfortunately my method of=20
construction has proven to be unreliable and it no longer works. =20
My next step was to pickup a basket case Harman-Kardon A-300 on =
ebay and=20
restore it to operation. I was quite surprised by the sound. After =
all it=20
had been 35 years since I had heard a tube amplifier. The H-K A-300 =
gives=20
about 10 or `12 watts per channel. I don't have any of the original =
literature on it but it uses a ruggedized version of the 6V6 so it =
can't be=20
much more than that. It has the same effortless sound as the 200 =
watt per=20
channel solid state had. =20
My Conclusion.
At the peak of tube technology 50 watts per =
channel=20
was plenty for most listeners. In the solid state age listeners =
pushed=20
manufacturers to higher and higher power in an attempt to get away =
from the=20
transient distortion that plagued those amplifiers. Evidently they =
succeeded somewhere above 200 watts per channel. The inherent =
cleanliness=20
of the tube sound makes it possible to return to sanity when it =
comes to=20
power levels.=20
It is true that there have been some super power tube amplifiers =
built=20
and sold but frankly I don't see the need for them unless some very=20
inefficient speaker systems are being used.=20
Speaker Efficiency.
The statement is often made that if =
you are=20
using air suspension speakers, once known as infinite baffle, you =
need a=20
higher power amplifier. I think this case is overstated. While =
there may=20
be one or two models of speaker systems that need a proverbial =
sledge hammer=20
to drive them most are not all that less efficient than a ducted =
port=20
system. I am using a pair of SPL 99 air suspension speakers with my =
A-300=20
and it sounds just fine at normal living room levels. I have run =
into some=20
clipping when listening to CDs at high volume. I will likely go up =
to 50=20
watts per channel and be happy with that.=20
Next;=20
A Low Distortion Gain Block.=20
Home=
=20
Or use your "Back" button to return to where you were.=20