D I O... P A P E R
by Steve Deckert
you're ready to adventure into the mystery of lower
power amplifiers and their appeal, you hope your research
quenches your biggest fear - that less power will be
first concern is; will it get loud enough followed
by what type of bass performance will it have.
After all it's a bit much to think a 50 to 250
watt system could ever be completely replaced by a 5
you don't feel like taking someone's word for it, the
best thing you can do is arm yourself with a better
understanding of what real power and dynamics are.
need to start with understanding the volume control.
In any given system you will slowly raise the volume
control to a certain point and stop. That becomes
your desired listening level. So, what made you stop
rotating at that exact point? Why not a click or two
before that spot, or perhaps a few notches past that
answer is largely about frequency balance and detail.
If you don't turn the volume up high enough, the
music lacks body and weight - it sounds a bit thin,
perhaps dry. Inner detail is also harder to distinguish
as the volume is not high enough to properly project
it. On the other hand if you turn the volume up
too high, the sound starts getting worse, not better.
This is due to distortions in the amplifier, speakers,
and or room acoustics, usually a little of each.
your speakers can handle the power of your amplifier
and your room is half way listenable, the special spot
on your volume control is determined more by the amplifier than
power amplifiers, say anything over 100 watts solid
state or 50 watts tube, will force the magic point on
the volume control higher before there is a nice bloom.
On the other hand lower power tube amplifiers generally
behave in a completely different manor. If you
look at the high power listening experience with
respect to the volume control, you could equate it to
speed limits on the highway where you have a minimum
speed of 45mph and a max speed of 65mph. The lower
power tube amp has no minimum speed limit.
a lower limit determining when the amp will sound good,
you can have fully developed detail, weight and bloom
even at 5mph! This can be (and is) rather
empowering because now you determine what level you
want to listen at, not the amplifier.
now that you understand that lower power tube gear has
more detail and weight at lower volumes than high power
amps lets talk about the other end of the spectrum.
POWER is the point on the volume control where an audiophile
will stop rotating when he or she is interested in playing
the amp as loud as it will go and still sound good.
It is that exact point on the dial when the sound
stops getting better and starts loosing ground. (Often
in high power amps this is the point when the amp shifts
from class A to class AB).
A operation is the least efficient form of amplifier
power, but by far the best sounding. It is a big
player in usable power.
amps have way more usable power than others. For
example, you can have an amplifier that is rated at
50 watts that has less usable power than an amp rated
at 20 watts. In fact when we developed the Torii
Mk II, a 25 watt amplifier, the design goal was to keep
the transparency of our smaller single ended amplifiers
and get as much usable power as possible. At the
same time we built a pair of 80 watt tube mono blocks
and a pair of 120 watt tube mono blocks to compete with
it. While both of the bigger amps would get louder,
it was the 25 watt Torii that we were able to play the
speakers loudest with. It had the most usable
power. When the sound quality isn't there at higher
volumes with a big amp the extra power is worthless.
Add to that the issue that they have to be turned
up a fair amount to get the bloom and you could say
the power on the low end of the scale is also worthless.
how does one get dynamics out of a small 5 watt amplifier?
Start by loosing the assumption that it is somehow
handicapped in that area. Pair it with an efficient
pair of speakers so you can play it loud if you want.
Dynamics are greater on low power tube amps matched
with high efficiency speakers than you'll be able to
get from a high power amp on low efficiency speakers
- aka the hi-fi industry. In a quiet
room with a low power amp and speakers of 94dB
or higher efficiency you can expect around 30 dB of
dynamic range in the first watt. (NOTE: It
takes a doubling of power to increase the volume by
3dB). When you add a second watt of power you
increase the dynamic range by only 3 more dB. If
you double the power again to 4 watts you'll gain
another 3dB and 8 watts gets you 3 more. By the
time you keep doubling your power to get that additional
30db you require 1024 watts. So obviously power
has a steep ramp of diminishing returns. a 100 watt
amp is only 3dB more power than a 50 watt amp, almost
FIRST WATT SUCKS WHY CONTINUE
has been my tag line in the forums for many years. But
consider the fact that many big audiophile loudspeakers
with multiple drivers and complex crossovers have not
the ability to resolve the first watt at a usable volume
level. This is because a portion of the first
watt is lost in the crossover network before it ever
reaches the drivers and because the drivers have too
much moving mass to be heard with what's left. So for
the mainstream hi-fi industry it all starts with the
second watt - meaning that first 30 dB of dynamic range
(music) is largely missing. It's not surprising
many audiophiles build large high power systems up to
1000 watts trying to reach a dynamic range of 30 dB
while at the same time some guy is sitting in his listening
room getting more than 30dB out of a 2 watt amplifier
with the appropriate speakers.
you have music playing at 60dB above the noise floor
in your room you're probably at an SPL of around 100dB.
(40dB noise floor + 60dB music) In that 60 dB
of dynamic range, the first 30 dB or so is all the ambience,
detail, and micro detail in the music.
POWER IS NOT AN AMPLIFIER TYPE
the tendency in this hobby is to put things in categories
let me take this opportunity to mention that not all
low power amps have a high percentage of usable power.
Some have nearly 100% usable power, while others
may have less than 50%. The determining factor is the
design of the amplifier itself. This is very obvious
when you start to evaluate different offerings from
different designers. The good designs will always
have higher ratios of usable power to total power than
the bad ones. There are less good designs than
bad ones in this hobby right now, more than ever in
fact as everyone including China has been jumping on
the "hey let's make a tube amp" bandwagon.
Neverthess when you look at several different
amplifiers and their rated power you will never see
a spec or any disscussion about USABLE POWER so assuming
you only tollerate the best sound and never rotate the
knob past the usable power limit, you really have no
idea how much power each amplifier really has.
POWER INTO LOAD
power can not be measured on a scope using a resistive
load which is how RMS power is measured. Speakers
are horribly complex loads involving varying resistance,
capacitance and inductance - not to mention the voltage
they reflect back to the amplifier. An amplifier's
ability to deal with this varies wildly from design
to design. How much power a given amplifier is able
to put on the voice coil is always different than the
amplifiers rated power. Kind of like engine horsepower
vs. rear wheel horsepower. But it's not just
the amount of power that reaches the voice coil - it's
how much of that power makes the speakers sound good.
(think of it as traction, or lack of tire spin)
It's how loud you can get that speaker to play before
it starts sounding bad.
is why a well built low power tube amp with all usable
power surprises so many audiophiles who try one for
the first time. Once I had a customer with Magnapans
who was on his 3rd 250 watt solid state amp and was
concluding that his maggies simply didn't have any bass.
I sent him home with a 2 watt Zen amp and while
we both knew it wouldn't get real loud, he was stunned
that his speakers now had convincing weight and bass
for the very first time since he's owned them. This
is an example of an amplifier being able to couple it's
power to a complex load.
usable power is largely enhanced with class A operation
you want to watch out for amps boasting high power figures
because they go into class AB operation quickly to get
the efficiency up. Take the following example:
A Zen amp uses a 150ma transformer that makes
around 400Volts DC after rectification. It has
two small output tubes each biased at 47ma and makes
about 2 watts per channel or about 6 watts in mono.
By employing techniques to increase efficiency,
such as fixed bias, push pull, ultralinear transformers
and bigger tubes I can get the same power transformer
to work in a 50 watt KT88 based amplifier. In fact I
can push it to 60 watts if I want to.
have seen designs that take a pair of output tubes to
nearly 80 watts that had less than 1 watt of usable
power. Nevertheless they would have 80 watts RMS
with low distortion - look pretty good on paper, sound
is just no reason to build amps beyond 50 watts if your
intent is to serve the music. If your intension
is to make money by building amps that will play today's
low efficiency hi-fi speakers then consider 50 watts
about the lower limit of the power range you should
be targeting for a successful business.
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by Steve Deckert