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Pass Laboratories X350 Stereo Power Amplifier Print E-mail
Tuesday, 01 August 2000
Article Index
Pass Laboratories X350 Stereo Power Amplifier
Page 2
ImageI received a call from my wife a few months back while I was traveling on business. She said that there was a box on the porch that she couldn’t possibly budge. I soon realized that it was the awaited Pass X350 that I was to receive for review. Knowing that it was heavy, I asked her to get a neighbor to help her drag it into the house. She later called and said that it was a huge job, even with a strong male helping. It wasn’t until I got home that I realized how massive and dense this box really was. From unpacking to positioning it onto my amp stand, this was a project. It weighs about 150 lbs., but that doesn’t tell the whole story. At 19 inches wide, 22 inches deep and 10.5 inches tall, the X350 is not a small amp, but it is not the largest by a long shot. However, it looks and feels as solid as a wrecking ball. Its front panel is constructed from a one-inch thick plate of aluminum with heavy machined front wings that dress a four-inch diameter power meter. The sides have been fitted with top to bottom heat sinks that at first appear to be overkill, but once this amp warms up, you see that the form fits function. The rear is simple yet fittingly sturdy, with large wingnuts for speaker connection. The price on the X350 is $9,000.

When powered up, the X350’s front power meter glows cool blue. It seemed to me like a window looking into a fish tank. I found it to be a very appealing feature. The funny thing is that the meter tells you nothing. I should perhaps rephrase this to say that it tells most of us nothing. What it reads is the amount of power being drawn from the wall into the amplifier’s power transformer. This means that when you turn the volume up, the meter needle moves but doesn’t provide you with any overly meaningful information. However, this said, I found the meter feature so aesthetically appealing that I would pay extra for it if necessary. Frankly, I find it to be visually astounding.

The Pass X350 is the largest stereo amplifier in the X line, their newer reference series, and a baby brother to the X600 and X1000 monoblocks. The X350 is rated at 350 watts at eight ohms. For those not familiar with the previous Pass products, for many years, Nelson Pass has been creating amplification that is considered by many to be among the very best that this industry has to offer. The Aleph series amplifiers of the past were run by some of the most discerning critics in the industry. Pass owns many patents for his amplifier designs, including multiple patents for the X series amplifiers.
The technology associated with the X350 amplifier is called Supersymmetry. The U.S. patent for this was issued to Pass back in 1994. The amplifier’s performance is achieved by using highly matched components in a simple balanced class A configuration. The X350 uses just two stages. These are inherently low distortion types of circuits, but their performance is improved when operated in balanced mode through cancellation. Distortion and noise identical to both halves of a balanced circuit will disappear at the output, and in a well-matched symmetric circuit, most of the distortion and noise is identical. Supersymmetry enhances this effect by providing a connection between the two halves of the balanced circuit that further perfects the match. Any distortion and noise not already identical to the two halves is made identical, and the result is improved cancellation at the output. You will find considerably more detail available with respect to design and engineering at the Pass Labs website listed at the end of this review.

After an approximate 200-hour break-in period, which is needed for nearly all amplifiers without question prior to any critical evaluation, it was time to hear what this powerhouse had to offer. One characteristic that became immediately apparent was the presence of detail and this amp’s superb dynamic range. Dynamic range refers to the range between the loudest and quietest pieces of information within the music. Dynamic range can be best evaluated in musical pieces containing detailed instruments of varying frequencies and volumes, such classical performances by an orchestra or a symphony. The Pass X350 did one of the best jobs I have heard in reproducing these details. The bass control of this amplifier was unquestionably superb, the best I have heard to date in my reference system. When listening to music with some dynamic impact, this amp had my Revel Studios hopping. The Revels are not particularly efficient - in fact, they are quite inefficient - but when driven with high power, they will knock you silly if you prefer to listen to music aggressively, as I do. The Pass provided bass control, along with the necessary finesse, without a hiccup.

The Music
When I review a product, I always start by just listening and just enjoying the music. It is counterproductive to try to assess a piece as soon as you receive it, because it not only takes time to break in a component, but it takes time to acclimate to the sound and determine what it is that is right and what is wrong.

Unless a component is bad, I will spend several weeks just enjoying the unit, saving critical judgment for later. One of the many albums that I listened to was Ellis and Branford Marsalis’ ‘Loved Ones’ (Columbia Records). The X350 recreated the instrumental timbre of the piano very well in this beautiful and open recording. The piano sat back nicely, yet had plenty of percussive dynamic impact. The X350 was decisively transparent and open.

When listening to Sister Hazel’s first album, ‘Somewhere More Familiar’ (Universal), the song "Starfish" is an excellent test for bass extension. At high volume, the kick drum got into my soul. It had enough bass slam to make my heart feel as if it were beating irregularly. During a drum solo, I love feeling as if someone is kicking me in the chest and the X350 provided that sensation. It has the power to drive every conceivable speaker to its fullest. Okay, you ask, if that’s the case, why do Pass and others sell amps that provide two and three times the power? Thanks for asking! Because, however impractical, until the gas shortages of the ‘70s, Chrysler manufactured a 426-Hemi engine that produced up to and exceeding 800 horsepower for the type of car body that my grandma owned. It’s the good ol’ American way. If one is good, two is twice as good! We Americans love excess! Otherwise, this amp is plenty capable of the toughest loads.


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