Product Review - Bruce Moore
Dual 70 Tube Power Amplifier - July, 2000
Bruce Moore Dual 70 Tube Power Amplifier
70 watts per channel ultralinear mode, 37 watts triode mode
20 Hz to 20 kHz @ 1 watt; 1%, 20 Hz to 20 kHz @ full power
Response: +0,-1 dB @ 1 Hz to 200 kHz (1 watt)
412 kOhm or 100 kOhm, depending upon date of manufacture.
1.3V for full output
4 & 8 Ohm Taps
Four 6922, Four 6550/KT88
Triode/ultralinear switch, independent biasing for each output tube
7.5" (191mm) H x 15" (381mm) W x 15" (381mm) D
|Bruce Moore Audio Design, Distributed by R.B. Electronics (Bob Bergner), 5492 Linden Street, Dublin, California 94568; Phone 925-875-1055; E-Mail [email protected] or [email protected]|
For readers coming to my reviews for the first time,
I currently review two channel equipment and classical recordings for Secrets.
Before long, I also expect to serve as its Music Editor.
Weaned on classical music, and specifically on old
opera ‘78s, I rediscovered opera and symphonic music when I was 11, and have
been hooked every since. While in my teenage years, I listened to Donovan,
Buddy Holly, and Little Richard just as frequently as Caruso (Little Richard
was played at high volume to drive my mother out of the house), classical
music increasingly became my first love. I turned many a head in my twenties
whenever I moved, because boxes of classical LPs stood out among the few
possessions I lugged from place to place. Both my performing career (see http://www.planeteria.net/home/whistler)
and equipment CD/performance reviewing have evolved naturally as music has
assumed greater and greater importance to my emotional and spiritual
You can be assured that, when I review equipment, I
am most concerned with how accurately it conveys ultimate musicality. My
reference, except in the case of synthesized and normally amplified music, is
always the sound of live music heard in a good, un-amplified acoustic setting.
Thanks to the San Francisco Symphony, the San Francisco Opera, the rich
concert series of Cal Performances and San Francisco Performances (two of the
best performance series in the U.S.), and my current work as an East Bay
performance reviewer, I have frequent opportunities to hear great music in
fine acoustic settings. I am even able, upon occasion, to sit everywhere from
first row center to the sides of the rear balcony. All this plus a fine sound
system have afforded me ample references for evaluating various equipment
This review continues my exploration of the Bruce
Moore line of tube amplifiers and preamplifiers. Background information on
designer Moore, who lives in Silicon Valley, may be found in my review of the
Bruce Moore Companion II-C tube preamp, located in the Secrets of Home Theater
and High Fidelity archives:
While the Dual 70 Stereo Power amplifier is designed
to work with a plethora of systems, it was specifically engineered to
complement the Bruce Moore Companion III preamp. Since that preamp (review
forthcoming) has become a treasured mainstay of my reference system, I
especially looked forward to hearing Bruce's amp paired with it in my
The amp can be preset to work in either 70 watt
ultralinear mode or 37 watt triode mode. Most clients prefer the 70-watt
setting, due to its greater power and dynamic range. Since my Chameleon III
speakers are not particularly sensitive, the amp was preset to operate in 70
watt ultralinear mode.
The Dual 70 offers both 8 Ohm and 4 Ohm speaker
connections. The binding posts are easily accessible on the rear of the amp
(far more comfortably spaced than those on my Pass Aleph 5, I must add). While
most 8 ohm speakers prefer the 8 Ohm connection, there are occasional rebels
that prefer the 4 ohm setting. My Chameleons were quite content with the 8 Ohm
Bias settings for each of the amp's four output
tubes are conveniently located on the lower front of the amp. All you need is
a simple screwdriver to adjust bias. You simply turn the knob shown on the
bottom left of the amp to choose which tube you're biasing. After noting
where the needle points on the front bias adjustment window (the round window
that dominates the front of the amp), you turn the appropriate bias adjustment
screw until the needle falls in the right place. Easy as pie. Bob Bergner, who
distributes the Moore products, suggests that bias be accomplished late at
night, when electricity is most uniform. Those who plug the amp into a PS
Audio P600 (or above) Power Plant can probably ignore this suggestion.
Most of the weight of the amp falls in front, where
the power supply is located. Please be aware of this when moving and situating
this component. Otherwise, you may discover it and you rocking one direction
or another. Given the options of broken tubes or a broken back, I lifted
consciously and chose neither.
I spent a significant amount of time with the Dual
mono 70, auditioning it not only with the Companion III preamp but with the
Wright and Parasound preamps previously reviewed for this site. For my last
test, I listened to it via Passive Attenuators, eliminating an active preamp
entirely. My reference amp throughout the audition process was my 60W Pass
Aleph 5, considered one of the simplest, most neutral, low distortion,
tube-like solid state amps of the recent past. Unfortunately, the Pass'
input impedance is a very low 10K Ohm, which does not make it an ideal match
for a tube preamp such as the Companion III. While it sounds so good with my
Companion III that I retain it as my reference, it must be acknowledged that
the much higher input impedance of the Bruce Moore amp makes for a better
One major difference between tube amps and solid
state amps is that the output of tube amps remains relatively constant over
the entire impedance response of the speaker, whereas the output of solid
state amps varies inversely to the impedance of the speaker. This is why tube
amps whose wattage equals that of solid state amps frequently sound both more
powerful and more dynamic.
This was certainly the case chez Serinus. What I
heard in dynamic difference between Pass and Bruce Moore far exceeded the
difference between 60W and 70W. The Dual mono 70 is as dynamic as all get out,
with the Moore amp/preamp combo definitely pushing the limits of my 14.5' x
17.5' x 9' listening area. This amp definitely deserves room to breathe.
The CDs employed for assessment were my usual
standbys. Not all are the last word in sonic excellence, but I have either
used them on many occasions or found their music so rewarding that hearing it
over and over again does not become a chore. These review discs, in no
particular order, include the Beethoven “Archduke Trio,” a 20 to 16 bit
recording played by the Chung Trio; Susan Graham's exquisite “La Belle
Epoque” Reynaldo Hahn song recital, recorded in 24 to 16 bits; the Bach
Brandenburg Concerti played with extraordinary verve and color by the Akademie
fur Alte Music, Berlin; the Blues No
More track of Terry Evans' JVC XRCD “Puttin' It Down;” the reverse
polarity beginning of Mahler's Symphony No. 6, conducted by Pierre Boulez (I
know, there are musically superior versions); and, based on extraordinary
sonic merit, the 24 to 16 bit Domenic Argento “Valentino Dances” on
Reference Recordings. Because I had recently reviewed it, and was thus quite
familiar with its sound, I also took a listen to Antonin Dvorak's Symphony
No. 9 conducted by Claudio Abbado.
In the course of many weeks of intense listening, I
accomplished several switches back and forth between the Pass and the Moore. I
also invited my “partner in high-end crime,” my friend Joey who began
building his own high-end system after hearing mine for the first time, to
come take a listen and tell me if he thought my perceptions were on the mark.
As a result, I feel that my conclusions are highly accurate.
All my conclusions result from tests conducted with
the active preamplifiers mentioned above. The passive attenuators, when
connected to either the Pass Aleph 5 or Moore Dual Mono 70, were fine on
highs, but failed to convey midrange and bass fullness. A significant part of
the tonal picture was lost, and what remained was not enough to facilitate
clear comparison. Despite frequent claims that the simplicity of passive
preamps and passive attenuators makes them ideal for many systems, I have so
far tried using either one or the other with three very different solid state
amps, and have never achieved success. Amps such as Pass, Moore and Krell seem
to need an active preamp in order to manifest their magic.
Furthermore, plans to isolate the sound of my various
interconnects by using the passive attenuators and switching interconnects
back and forth – a test that would make me even more aware of what was
responsible for what I was hearing when auditioning equipment -- had to be
scrapped because a faulty locking termination on one of my Taras would not
open far enough to allow me to attach it to a passive attenuator. The Tara has
since been repaired under lifetime warranty.
The Bruce Moore amp excels in the following areas:
Depth. Whether depth signals are actually embedded in a recording, or the
product of electronic hocus pocus, they help compensate for the reduction in
listening area size from concert hall dimensions to one's living room. The
Moore amp definitely conveys depth, more depth than the Pass.
Sound of the hall. I don't know if it's because of the Pass's less
than perfect input impedance match with my tubed preamp, but the Pass has
never fully convinced me that I am hearing the “sound of the hall” touted
in many audio reviews. With the Moore, I know that such claims are not thin
air. Having a visceral sense of sound bouncing off walls, as opposed to a
generalized sense of reverb, made listening quite compelling.
Lower midrange and bass, bass, bass. The Dual Mono 70 has them both, so
rich, controlled and powerful that I had to turn down my subwoofer amps
(connected to the preamps' tape outputs) in order to balance the subs with
my main Chameleon speakers. The Dual Mono 70's bass is also the tightest and
fastest I have heard in my system. It is mighty impressive, natural sounding,
and totally satisfying – the best I have heard in my system.
Highs. The highs on the Dual 70 are quite vivid without being overly
bright. I found them quite pleasing.
Power and ease. Even on the most complex and demanding orchestral
passages, there was never a sense that this amp was being pushed beyond its
limits. Rather, the problem was that the volume increments between detents on
the Companion III preamp were too great to allow proper volume adjustment in
my size room for an amp this dynamic. In fact, even the very first preamp
volume setting resulted in volume too loud for late night apartment listening.
If you use a preamp with detented volume controls, it may need to be
readjusted to supply the ideal volume settings called for by such a powerful
Pace. The pace of this amp was superb. Everything sounded solid, crisp and
perfectly timed. Never did a drum stick sound like a spatula (something I have
heard on an inferior preamp). Anything you have heard about a tube preamp
sounding fuzzy or less focused than a solid state amp does not apply.
Noise floor, vividness of presentation and transparency. There is a sense
of reality that I experienced with this amp that exceeded that heard with my
Aleph 5/ Companion III combo. Part of this I ascribe to a very low noise floor
and resultant transparency.
Another reason may simply be this amps extra power, superior design, and
perfect match with the preamp. All I know is that, on one level, everything
sounded more involving, vivid and real.
After reading all this, you may wonder why I did not
pass on my Pass amp and replace it with the “perfect complement” to my
Companion III preamp, the Bruce Moore Dual Mono 70. Funny you should ask . . .
Before I owned the Pass, I owned a Krell KSA 50-S. I
once heard a manufacturer of superb cables call my 50W Krell the best amp that
Dan d'Agostino ever designed. Perhaps if I had paired the Krell with my
current Companion III preamp, I would have been able to comment on this
assertion with a semblance of surety. All I know is that, when paired with my
Classe 6 preamp (now used only for phono), the Krell
created an amazing, huge, three-dimensional, space age soundstage that
seemed a bit more like a psychedelic experience than one related to the sonic
reality of unaltered consciousness;
had enough slam to make my downstairs neighbor bang her broomstick on the
ceiling to get me to turn the music down; and
had a combination of a recessed midrange and across the board sweetness
that eventually drove me nuts.
With the Krell, everything sounded sweet sweet sweet,
from sweet-voiced sopranos to cacophonous 20th century orchestral
fare. Music that should have chilled my soul or reminded me of the horrors of
war instead sounded sweet. Drum thwacks had a sweet edge, brass had a sweet
edge, even sour notes had a sweet edge. Gaaah! I grew to hate it. Is there any
wonder that I went from the Krell to the neutral sounding Pass?
The Bruce Moore is nothing like the Krell. Its
soundstage seems real and convincing, and its slam achieves perfect
integration with the rest of the sonic spectrum. It also has a glorious
midrange, one that deeply impresses. But I do not find its timbre entirely
true. Everything is just a little bit shinier and sweeter than I find it in
The analogy I come up with is of looking through a
window. If we posit, rightly or wrongly, that the ultra-simple Pass offers a
view through a clear window, then I'd say that the Moore's window has a
bit of a shine to it. It is a beautiful shine, very inviting and seductive. It
certainly does not obscure the view, or alter one's feeling about what rests
on the other side of the window. But it's one of those shines that makes
everything on the other side seem to have a little bit of mother of pearl
Compared to the Moore, the Pass sounds most
unglamorous. Just as many will find that a person's natural beauty is
enhanced with even a touch of make-up, many will prefer the slightly glamorous
shine of the Moore. After all, it only serves to further drive home how clean,
rich, full, deep, solid and impressive this amp is. Alas, this extra little
bit of sweetness, which the Moore shares with many other tube products, is not
what I seek. I want to hear music just as it is, heaven and its hell, warts
For reasons I hope to be able to pinpoint clearly as
I test more speaker cables, interconnects and power cords in my system, my
current equipment configuration conveys the reverb around instruments and in
acoustic spaces as occasionally sounding a tinge gray and powdery. This is
especially true on some (not all) chamber music recordings. “Space” does
not always sound the same as it does in real life. The Moore does not do this.
Both reverberation around instruments, and the sound of the hall, are quite
convincing through the Moore; instruments and voices stand out in vivid color.
But the Moore's slight extra shine, glamour and sweetness are not real. As
much as I love many of the Moore's qualities, I prefer a more neutral sound.
While, with the Pass connected to the rest of my current equipment/cable
configuration, a cello may sound less brilliant and rich than in real life,
what it does sound like is as close to the sound of a cello as I have yet
heard reproduced in my 14.5 x 17.5 x 9 listening room.
I wish to make one more point.
Bruce Moore products are designed by one man, who in turn has one major
distributor who in turn serves both other distributors and his own customers.
All the people I have met or communicated with in the Bruce Moore circle are
fine men, men of the highest integrity who love what they do. But they are not
always easily accessible when it comes to service. As many readers know, this
is true for many small operations. There is an advantage to working with a
large company that really is there to answer the phone during the “normal
business hours” of this anything but normal industry. The advantage is moot
when one large company wanted to charge hundreds of dollars for replacement
stenciling of front panel lettering on a $3,200 preamp whose inexpensive
stenciled lettering had worn off, or when another company promised immediate
upgrading for a piece of equipment, but ended up holding it for weeks until
the parts arrived. But when a company combines regular accessibility with
integrity, there is a distinct advantage. The Moore operation would benefit
from a second in command who can help expedite service issues.
I review CDs for two newspapers that insist that I
state all my opinions as though they are absolute fact. To write “I feel”
in such a review is, according to the editors of those publications, to draw
undue attention away from the music and towards myself.
Tell me, what is the life of music without the
listener? Just what is the sound of one hand clapping?
I do not pretend that my reviews are more than a
reflection of how I choose to experience reality. My hope, however, is that I
provide you with enough clues about myself and my values to enable you to
sense if your viewpoint may prove in synch with my own.
In many respects, the Bruce Moore Dual 70 is the
finest amp I have yet auditioned in my system. Matched with the right preamp
and cables, I have absolute certainty that it will bring great pleasure to
many. I also am equally certain that, while my criticism may speak to some,
others will find my reservations an indication that this amp is right for
Bruce Moore is a superb designer, and his value-laden products deserve your attention. This amp can stand comparison with many name brand amps that consistently receive praise in the audiophile press. I encourage you to take a listen.
Chameleon III tunable speakers (modified with Nirvana hook-up wire and Scan Speak 2905/9700 tweeters);
powered subwoofers (stereo pair)
PASS Aleph 5
60W pure Class A power amplifier
Companion III tube preamp
Theta Gen. 5A
Digital Lens with BNC in and out
PS Audio P300
AQ Dragon II
speaker cable to the Chameleons
AQ Clear II
speaker cable to the Hsus
interconnect between amp and preamp
AQ Diamond II
co-ax interconnect from Hsu amps to preamp
interconnect between preamp and DAC
digital (BNC) interconnects from Theta to Lens and Lens to transport
by MIT, Synergistic, Harmonic Technology and XLO
Michael Green Deluxe Ultrarack and Basic Racks; MG Audiopoints and room treatment; Black Diamond Racing Cones; inner tubes, maple cutting boards and bags of sand, homemade bass traps; Shakti stone and many Shakti On-Lines; Bedini Ultraclarifier, Audioprism Stoplight and Blacklight
- Jason Serinus
© Copyright 2000 Secrets of Home
Theater & High Fidelity
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