Function And Pass Aleph 3 Power Amplifier
Most people thing design is about appearances —looking good, chic or
expensive. Yet when one of the world's leading designers, Kenneth Grange of Pentagram, was
recently asked to select an exemplar of good design for the BBC's design awards. he
displayed on national television—a ball of string. His point? Function is the single
most important criterion by which to judge any design's worth, and function encompasses
primarily, for our selfish human species, the way the tool (metaphorically or literally)
fits our hand.
I have always admired the aircraft designer's maxim for designing
airframes— simplify and lighten. If we want to apply this thinking in other realms,
we can take lightness to mean absence—of superfluous mechanisms, functions,
capabilities. Why build it to perform one iota above the specification of needed
performance parameters if that capability adds weight, manufacturing expense, maintenance
charges or fuel consumption?
When a good engineer has finished simplifying an aircraft design, the
completed object has a very special form of beauty, like that of a bird. As sculptors say,
just remove all the material that isn't needed and there's the finished sculpture. Ask an
electrical engineer to do the same and you'll he rewarded with a single-ended amplifier [
Ed. Note: A number of designers would take issue with a single-ended circuit's being all
that is necessary!] Ask Nelson Pass to do it and he'll keep on going until the amplifier
comprises a single active stage of amplification, although he concedes this is, to return
to our aircraft analogy, a micro-Iight. “It's like the talking dog'', he says,
“it's not how well or badly it talks, but that it talks at all.''
Pass's Talking Dog? The Aleph Design
These amplifiers' circuits will he published soon for the curious to
recreate for themselves: meanwhile the design exercise has yielded the most exciting and
rewarding fruit of all: it has enabled Pass to remove a stage of amplification from the
Aleph design and to lower the cost of the product—the ultimate payoff. At the same
time, he has seen an opportunity to fill a gap in the specification—the Aleph 3 is
limited to 30 watts per channel output. What's the big deal about less power? Simply
this—if you accept the proposition that 30 watts is enough power to drive any
sensibly designed loudspeaker (I do wholeheartedly), you can achieve this power by running
the amplifier in true class A. This is the least efficient mode, because it draws full
power from your wall socket all the time the amp is switched on, in the case of the Aleph
3, 250 watts or the equivalent of a few light bulbs. In turn, this makes the amp less
sensitive to those disturbances in the power line caused by constantly varying power draw,
which not only pollutes the amplifier's ability to supply itself with sufficient power but
also affects the ability of the power line to supply other components operating on the
same line.
Living in New York has made me acutely aware of these problems and I
commend the balance struck in the design of the Aleph 3, which should even make it
possible to listen in summer when all the air conditioners are switched on! After all,
what is the use of the best electronic music box in the world if you can't use it whenever
you want? Pass has also paid attention to human frailty with this design: you can short
the outputs, plug and unplug outputs (deliberately or accidentally!), and still the amp
goes on functioning perfectly. Try this with some other designs. and you'll be sending the
product off for service!
I have admired the casework of this design since the appearance of the
Aleph O, with which it shares the use of pre-existing heat sinks. These are machined to
accommodate fastenings and openings for connectors and other appurtenances and assembled
into a truncated cube—so much more elegant than a rack mount that will never be used
but whose solid, milled faceplate justifies another kilo-buck on the price tag.
And Function!
And now we come at last to the purpose of it all, the sound. Before the
arrival of the Aleph 3. I added to my system an N.E.W. A-20. This is a very different
product based upon Nelson Pass's A-40 published in Audio Amateur in 1978. Although Pass
had no hand in the development of the A-20 and is not associated with N.E.W. in any way. I
thought the A-20 would illustrate the movement and direction Pass's design philosophy has
taken over the time between the appearance of the two designs. I set the A-20 to drive
Quad 63s and, as is usual when substituting one component for another, found I had to
change the position of the Quads to obtain the best results. Every component I've tried
has its own unique way of dealing with the harmonic structure of music. The room has the
greatest effect of all, so you never listen to the music or the components but instead you
listen primarily to the room! Peter Walker of Quad once told me that changing loudspeakers
has less effect than moving the same loudspeaker by 3 inches in the room. He conducts the
imaginary exercise of visualizing the room surfaces covered by mirrored glass, and then
noting how many reflections of the speaker are visible to the listener. The number is in
the thousands, as reflections are reflected in turn at each mirrored surface The
reinforcement and cancellation that occur whenever the sound hits these reflection points
will give a wildly varying character to the perceived sound in the room, and varying the
positioning of the sound sources will make the sound seem brighter or warmer, more direct
or more reverberant —the same character traits ascribed to different concert halls or
modifications to the performing stages in those halls.
The position I settled on with the A-20 gave a wonderfully easy, direct
sound that allowed each detail to emerge from the musical background. Then I replaced the
A-20 with the Aleph 3. Immediately the upper registers receded, turning this room from
Avery Fisher Hall with its bright clear sound into the warmer sound of Carnegie Hall. And
where we listened from the balcony in Avery Fisher before, now we listened from the first
rows at stage level in Carnegie. The cellos grunted and buzzed, the bass was handled in
that euphonic Carnegie way that never allows the notes to pile up on each other, but -
perhaps a little more attention should be paid to the violins? (As I continue to use the
amplifier, however I find the soft treble to be progressively alleviated.)
Meanwhile, the Quads were turned to direct maximum treble straight into my
ears at the position where I listen, and this restored the balance of the sound to include
the higher notes and harmonics, including recording faults.
Now this positioning of the Quads I know from long experience will be
tolerable only with systems that either roll off the higher frequencies or, rarely,
present all the information in a truly balanced way that does not overemphasize the faults
inherent in the recording process. The phase aberrations that cause voices, particularly,
to lurch about the stage as though the performers were suspended on flying harnesses, were
here clearly evident but easily acceptable in the midst of the riches of direct musical
information.
The characteristic of the Aleph 3 that most engaged my ear in this early
stage was the ability of the circuit to get out of its own way, a deftness and nimbleness
that revealed resonances in the recording without adding to them, a presentation of
transient information - for example, triangle strikes in which the note sounded clearly
and then stopped as the harmonics faded. This effect also extended to the instruments
themselves, as it allowed one instrument to avoid stepping on another. allowing me to hear
the separate contributions and the resulting unison effect simultaneously— more like
the effect of live music. I am not referring to the physical position of instruments,
which I find simply detracts from the music. The effect I'm discussing is present in live
music as well as on a really good mono system, and that is simply a reduction in the
blurring found in most electronically recorded and reconstituted music.
As time has passed, I have found this configuration of my system has
weathered well, as it combines two cardinal virtues— it continues to work with no
nasty surprises and, more importantly, it has what I like to think of as the Ancient
Mariner quality: when you least expect it, it reaches out a musical arm to hi-jack your
attention and leads you into the labyrinth of a musical story without forcing you to be
aware of the machinery behind the illusion.
In conclusion, the Aleph 3 represents a bullet-proof, zero-maintenance
solution for the person who w ants to try single-ended with no complications—heartily
commended. Now if only Nelson Pass can persuade some company like Sony to commission a
single-ended audio-amplifier chip for use in televisions, computer sound boards and, of
course, all their other audio products, we'll really be making some progress! |
