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Equipment Review No. 3  MAY 2001
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The Power Modules 150A Power Amplifier
by David Belles
$1,195. www.powermodules.com
In the past I have referred to this amplifier in the reviews of other components, but only recently did I realize that I had never written a review of the 150A. Oh, Dave I'm really sorry. But being the gentleman that Dave Belles is, he never called or complained about my indiscretion, he just went about his business as usual.
 
It was the review of the JPS Grey Power Cord. I had been using the 150A and the Coda 10A, and my results with both amps had been good, but it wasn't until I started using the
JPS with the 150A that I knew how well either component was
truly capable of performing. I ended up using the JPS power
cord with the 150A power amp driving the Merlin VSM, and the
results, my friend, were wonderful... absolutely wonderful.
 
The 150A has a power output of 124 wpc at 8 Ohms and 225
wpc into 4 Ohms. Damping factor is 200, and the input impedance is 100,000 Ohms. The 150A weighs 33 lbs., and its dimensions are 6.26" high, 17" wide and 13" deep. The 150A
utilizes Hitachi MOSFET output devices (four per channel). It measured just slightly better with the AC polarity reversed, it also sounded best with the AC reversed.
 
The 150A has an unassuming appearance looking rather like the prototypical power amp of the 1980's... black rectangular chassis, heat sinks on the sides, power button on the front, one set of speaker terminals.
Nothing fancy to look at, and if you are into ego audio, look somewhere
else.
 
There presently are four power amplifiers that I recommend
at the thousand dollar price point. One is the Parasound
HCA-1500. It is an incredibly punchy amplifier (205 wpc)
for the money that really delivers the juice into a load (1
kVA transformer and 8 bipolar outputs per channel). Of the
"thousand dollar babies", the 1500 is probably the most
powerful with the tightest, driving bass. It is also the
one most obviously build to a price point in terms of
boards, chassis and overall construction.
 
Another is the Odyssey Stratos at $995. The Stratos is a
fully discreet design utilizing Sanken bipolar output
devices for 150 wpc. This is big league sound for minor
league money... solid, dimensional and smooth. I love it,
RW Weiner loves it... there's nothing not to like here.
 
From over the hill and far away comes the ME 550 from
Australia (100 wpc). For about $1,300 US dollars one gets a
super sophisticated design that sounds spacious and
tube-like, a real down under surprise.
 
And then there is the 150A from David Belles. Looking
under the hood reveals an amplifier that appears mundane and
conventional, nothing extraordinary to look at. And at
first listen, the amp doesn't particularly impress. But
after about three weeks break-in the sonics were a whole
different can of silicon. First came the JPS Grey Power
Cord - WOW, synergy defined between two elements... I
literally heard the amplifier come alive! It was major,
baby!
 
Then I flopped the AC polarity for another improvement, not
as dramatic as the insertion of the JPS power cord, but very
real in terms of staging. Then I hooked up the Merlin VSM
SE loudspeakers, and the Herron tube preamp. Put the
emphasis on "tube preamp". The input impedance of the 150A
is 100,000 Ohms, and as everyone knows a tube preamp loves
to drive an input impedance of 100,000 Ohms. I also loved
this amp with the Aronov tube preamp. What I didn't love
with the 150A was David's own 15A preamp. That cute little
15A sounded best with transistor power amps with input
impedances less than that of the 150A. With the 150A power
amp, tube preamps rule.
 
One last set-up tip. The 150A should not be considered a
"current" amplifier. It will not drive low impedance
loudspeakers the way the Krells, Sierras and Claytons can.
It will not double its power output into 4 Ohms. In the
case of the 150A, I wouldn't necessarily shy away from a 4
Ohm speaker, but I would stay away from speakers that
hovered around 4 Ohms and had serious dips into the 2 Ohm or
lower netherland. And while the amp is rated for more than
100 wpc channel, there are more powerful sounding 100 wpc
channel amps around. The 150A is not a weak sounding
amplifier by any means, but it doesn't come off as a Clayton
or the SimAudio W3 which have the same 100 wpc output rating
(the W3 is a locomotive). So, use a loudspeaker of at least
modest efficiency with this amp, 88 dB and above should do
it, and keep the impedance up.
 
Okay, when everything is set-up just right this amplifier
can steal your head and your heart. I have read Sam
Tellig's comments on the 150A, and I have to conclude that
he didn't optimize the power cord used, and that he didn't
reverse the AC polarity. Why? Because, while the 150A
sounds as gorgeous and sweet as he described, it isn't as
tubey sounding or as soft as he indicated.
 
First of all, had he used the JPS power cord he wouldn't
have been critical of the highs or the lack of a pristine
quality way up there. His review would have contained fewer
tube related adjectives such as "rich, romantic, rounded..."
because with the JPS, the 150A is more honest than that.
Nor would he have preferred "bloomy" and "ripe", to
"contoured" and "complete." What he confused for MOSFET
romance was simply not using the right power cord. Because
when you use the JPS, the amp can convey "rich, romantic and
rounded", but it also can do "fast, articulate and
transparent." It's an amp for all seasons.
 
And about this amp having MOSFETs at its output. MOSFETs
rightfully have the reputation for being a little hazy and a
little indistinct (Sam properly coined the phase "MOSFET
mist" some years ago), particularly when run at low bias
levels - fake tube sound from a transistor can be the worst
of all worlds. For those reasons, I have in the past been a
fan primarily of bipolar output stages. There recently have
been some exceptions to this rule which would have to
include the Sierra Denali, the most recent Monarchy mono
designs, and yes, the 150A.
 
This amplifier images a soundstage as believably as I have
ever heard - tube or transistor (though the new Bartha amp
threatens that status). This ability of the 150A to convey
the natural spatial characteristics of a recording, is to me
its most prominent and positive characteristic. Music can
sound nice and beautiful, but one has to realize that every
recording is made in a real space, regardless of where it is
made (save some electronic space stuff). Few power
amplifiers define and reveal the original recording venue as
precisely and naturally as does this one. It does so
without exaggeration or diminution of the elements within
that stage, and I think it is this striking ability that
sets the 150A apart from its competition. I had the 150A
and the Coda 10A in and out of the Big Rig quite a bit
during the evaluation period, and while the Coda had an
entirely different set-up agenda, it was clear that the 10A,
albeit a fine imager, was not as accomplished as the 150A in
that regard.
 
The bass from the 150A is sufficient for a fine listen, but
it won't be confused with the taught force found with some
of the current monsters. This is the one area where
bipolars still have the advantage, but even there the
difference is diminishing.
 
Conclusion. After the 150A was entirely dialed in, it
struck me as a highly refined example of a brilliant man's
life work. It's not a perfect power amplifier; it could
carry more weight across the bandwidth as the Clayton
M-100's do, and it would be improved if it could carry the
sting of a leading edge transient with the alacrity of the
W3, but those things were clearly not the ultimate
priorities in the design of this amp. Yes, they are
important, but within the financial constraints chosen for
the 150A, Dave has dialed in on those things which he thinks
the music needs most and then optimized his design for them.
In ways that seem almost uncanny, the 150A is an amp that
goes for the musical jugular, and gets it. I'm sure that
Dave could refine this design even further, but I expect
that is what the 350A is for ($3,500). For the money, this
is a marvelous work.
 
- Martin DeWulf
 
Reprinted with permission from: Bound for Sound Report
Martin G. DeWulf, Editor & Publisher
108 East Division Street, Kewanee IL 61443
309.856.5515   309.853.3193 fax
E-mail: bfshifi@cin.net

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