Audiomat Prelude Reference 20
Ting and bang with class.
Review By Neil Walker
here to e-mail reviewer.
moved and inspired.
Me, that is, after listening to the Audiomat Prelude Reference 20
integrated amplifier. Listening to the 20 also raised a question: how
often does a piece of audio gear create self pity in the reviewer?
Five years ago, the Audiomat Prelude Reference amplifier
impressed me with its resolution, accuracy, speed and musicality. It
impressed me so much that I sold my trusty Audiomat Arpege and purchased
the Reference. It has not disappointed me since its arrival. It still has
the speed, faithfulness and musical presence that I noted in my review. It
still has great bass slam, detailed mid-range and transparent uppermost
frequencies. Nothing that a carefully voiced high-current amplifier should
not deliver. However, not too long ago, I reviewed the Audiomat Opera
integrated amplifier elsewhere. It was a great experience — as I wrote at the
time, Shirley Horn’s album, You Won’t Forget Me, left me
sleepless with excitement from the musical magic the Opera created.
Now, here I am again, somewhat rattled by the experience
of listening to great music on an excellent amplifier. Although the 20
does not possess the magical qualities of the Opera, it compensates in
other ways. The Opera gets its magic not only from
first-rate components and design, but also from its ancient secret. It is
a Class A amplifier — 100 percent Class A. Before someone starts with
some corny jokes about “Class A — at that price it oughta be Class
AAA++,” let me explain. If you already know the distinctions among Class
A, Class B and Class AB amplifiers, skip the next paragraph.
The simplest way, if not the most accurate, to
understand the difference between a Class A and a Class AB audio
amplifier, is to think of an amplifier as a — wait a minute, that
doesn’t work either. In a simple vacuum tube or valve, (let’s use this
word instead of vacuum tube — saves keystrokes) there are three
essential parts, a cathode, an anode and, between these two, a grid.
Current flows from the cathode (negative) to the anode (positive) when the
voltage applied to the grid allows it to do so. Thus, when you apply a
voltage to the grid in a valve, the anode current flow increases. In a
class A amplifier, there is always a voltage applied to the grid, so that
there is always a current flow from the anode.
In a Class A amplifier, both halves of a signal (the
upper and lower halves, say, of a sine wave) are applied to the grid,
since the signal on the grid can increase and can also decrease to reflect
what is happening when the lower half of the signal or the lower half of a
sine wave is applied to the grid. The Class A amplifier produces an
increased current that matches in its varying quantity the variations in
voltage applied to the grid. When a varying voltage, such as an audio
frequency signal, is applied to the grid, the current flow from the anode
increase proportionately; its output is an analogue of the input voltage
applied to the grid.
In a Class B amplifier, there is no continuous voltage
applied to the grid, so that, when a varying signal such as an audio
signal, that contains both positive and negative as above is applied to
the grid, only half of the signal is reflected in the anode’s current.
As a result, the B class amplifier’s output signal is distorted and
incomplete. The first step in a solution is to create a two-valve output,
called a push-pull arrangement, where each valve amplifies one half of the
signal. Now, the output contains a complete analogue of the input voltage.
But a problem remains. The juncture between the two
tubes’ output signal is not going to be a perfect fit. As a result,
there can still be a number of unpleasant bits of noises unrelated to the
audio signal you applied to the two grids. The solution is a type AB
amplifier where there is a constant voltage applied to the grid of each
valve, but at a lower level than the voltage applied in a type A
amplifier. Doing this allows a small degree of amplification of the bottom
side of the audio wave signal applied to the grid in each tube. In a
two-valve, push-pull system, there is now an overlap between the two
amplifier valves — the valves are now covering the null point between
the high and low, plus or minus, of the signal that we are amplifying.
The Class A amplifier, since it is always producing a
full current, runs hot and is inefficient, with a theoretical maximum
efficiency of 50 per cent. It is always running at 100 per cent of
possible output. The Class AB amplifier, the engineers tell us, has a
theoretical maximum efficiency slightly higher than 75 per cent and thus
also runs cooler. However, the Class A amplifier still produces the
cleanest, most musical sound — as long as heat and electricity
consumption are not at issue. Thus, the biggest difference between the
Opera amplifier and the Prelude Reference 20 is the difference between
pure Class A and Class AB amplification. Thus, the manufacturer may apply
a substantial voltage to the grid of the AB amplifier and validly make the
claim that it operates in Class A up to one half of full power.
In the example of the 20 and the Opera, we are dealing
with two high current amplifiers that put the energy into different parts
of their task, one strong bass and treble, the other the exceptional
smoothness, the magic to which I referred, of the Opera. Thus, I
discovered a new soundscape listening to any of the recordings with the
Prelude Reference 20 that I had used to review the Opera. I think of it as
the soundscape of my youth. Powerful bass, crisp, detailed, able to both
reproduce music at low frequencies as well as push large quantities of air
back and forth. The highs benefit in similar fashion. A high current
amplifier has the ability to make undistorted, easy-to-listen-to high
notes and musical harmonics. In reproducing a bass note so that it sounds
like a musical note from a recognizable musical instrument, the harmonics
set off during the attack phase of the note are what make the musical part
of the reproduction.
“Nuages,” the first cut on James Carter’s CD Chasin’
The Gypsy [Atlantic CD CD83304] is one of my favorites for reviewing.
I once took it, a regular production CD; into a listening room for an
excellent high-end system at the Montréal audio show. At the end of the
piece, the room was in almost breathless silence as the dozen or so
people, including the sales persons, gathered themselves to return to the
mundane. “Not bad for 20 bucks a pop,” is what I wanted to proclaim,
but I behaved myself.
I love to hear the baritone saxophone’s reed start the
opening notes with a snap. The flaw that “hi-fi” brings to sound like
this is to make it seem more like a sound effect than like what it is, a
vibrating piece of wood in a brass pipe. Because the bari sax takes on a
lower register, it is a relatively large piece of wood that Carter sets in
motion. The difference in the 20’s sound is that these low notes and the
high pitch that the reed’s snap produces have a little more juice than
does the Opera. The sound is a fatter one than the Opera produces. The
accordion sections in this piece as the 20 presents them are more emphatic
sounding than when the Opera is playing them. But these instruments and
the intricacies of their sound stop well short of being just a hi-fi sound
Because of the additional current that this amplifier
makes available, it is able to reproduce a cleaner, tougher sounding bass
than the Prelude Reference. The bass drum in a recording such as the
AThunder and Lightning Polka” on the RCA Red Seal vinyl Strausse
Waltzes [Fritz Reiner and the Chicago Symphony Orchestra, LSC-2500]
emerges with great authority played on the 20 — a good demonstration.
The bass line in a pop song such as The Black Eyed Peas’ “Don’t
Phunk With My Heart” [Monkey Business] announces itself with
clarity and a lot of force. Here, I do not refer to force as in the door
rattling dumb-thump beloved of dB-addicted goofs and their giant
automobile sound systems (they didn’t start as goofs, but all that
vibration not only destroys your hearing, I suspect it scrambles the
cerebral cortex). Rather, what you enjoy is the sound of a bass musical
instrument, whether it is a genuine guitar or an electronic simulacrum of
generic bass instrument. Add a luminous quality to the 20’s power in a
strong bass line and you are getting close to what this most recent
iteration of the Prelude Reference does for you.
A well-recorded pipe organ is perhaps a better way of
demonstrating bass response. Nicolas Kynaston playing Liszt’s
“Funerailles” on the Klais Organ of Ingolstadt, Münster [Carlton
Classics 30366 00032] is a classical recording that stretches your system
into the lower range of 25Hz to 40Hz. The 20 takes hold of the speakers in
a way that you think is unlike anything you have heard before. While not
magical, its reproduction provokes a visceral response to the music. Liszt
uses the organ to create an up-front emotional response this music takes
you by the shirtfront and rattles your head against the wall. So does your
speaker system, if it can handle 30Hz or so. That is what the 20 does to
such excellent effect.
Another example is the bass and percussion accompaniment
to the musically simpler song “Fever” as Elvis Presley performs it [Elvis
Is Back DCC Compact Classics LPZ-2037]. When the 20 handles this
music, the accompaniment is gripping. Not only does one hear the wood of
the bass viol and the brass of the cymbal (this is an excellent
recording), but the 20’s precision and power exercise absolute control.
Thus, you get a realistic sounding bass and cymbal, not to mention of
course, Elvis’s voice up front and centre — this amplifier also
presents an accurate sound stage. Transient response is the most important
aspect of musical reproduction since most musical instruments at a given
pitch sound very similar to each other — it is the initial sound of the
note that tells one right away whether you are hearing a violin, organ or
Shirley Horn’s rendition of “If You Leave Me” from
her album You Won’t Forget Me, is one that begs for superb
amplification — the CD is so well recorded that not only is Horn’s
voice warm, close and detailed, so is her piano and the accompaniment of
drums, cymbals, wooden block, and the rest of the group’s instruments.
Yes, as with the other good amplifier’s I have reviewed, you hear the
cymbal’s metal, the wood of the block, the complexity of piano and
voice. But the 20, with its surplus of current on tap, etches these
details more firmly.
Most of the Audiomat amplifiers are rated at 30 watts
and have very similar sets of valves. The company presents the best
argument I have encountered regarding the insufficiency of standard
specifications for evaluating a piece of electronic audio gear. Only when
you look inside and see the differences in transformers and capacitors in
the power supply and in the output stages do you begin to understand how
one amplifier whose specifications are the same as another can sound s
different. The next step is seeing no difference but hearing a big
difference because the transformers, although seemingly identical, are
constructed of better materials — and beyond that are the capacitors and
resistors, the material used in the circuit boards and the wire used to
connect each part to the rest of the amplifier.
Thus, the difference in sound and price. And,
in the case of the Prelude Reference 20, thus the creation of an amplifier
that is different from the Opera, but of equal merit —
depending on your criteria. Now that the Opera has been released in a Reference version, it presumably combines the virtues of the Prelude Reference 20 with the magic of the
100 percent Class A Opera. As a result, the decision becomes just a little tougher, depending on what your budget dictates.
Type: Integrated stereo amplifier
Tubes Compliment: Three 5965 for driver
stage, four EL34 for output
Power Output: 30 wpc @ 8 Ohms (Class A up
to 15 watts)
Frequency Response: 20Hz to 100kHz (-3dB)
Sensitivity: 350 mV
Inputs: Five stereo pair via RCA
Output: One stereo pair via RCA
Speaker Connectors: four for bi-wiring
Output Taps: 4 or 8 Ohms
Potentiometer Motorized ALPS
Input switches Lucas mechanical switch
Available Finishes: Brushed aluminum or anodized black
Warranty (North America) Basic: 90 days
Extended: 2 years
Weight: 47.2 lbs.
Dimensions: 17.5 x 7.5 x 16.75 (WxHxD in
Price: $6,490 CAD
10 Gaston Dumoulin
Blainville, Qc. Canada
Voice: (514) 221-2160