Equipment Review No. 3  MAY 2001

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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