The X150 embodies much of the same technology as the larger amplifiers in the series, and it closely resembles the X350. At the core of this amplifier is the patented Supersymmetry™ circuitry, which provides the fundamental technology used in the balanced design of this amplifier and claims to reduce distortion and noise by an order of magnitude over other matching techniques. From reading the design literature that is readily available from Pass on their website, I learned that for SuperSymmetry to work properly the amplifier requires a balanced input signal. Immediately I thought this design imposed a limitation on users. I decided to call the people at Pass to get a clarification on the design. They told me to support the needs of those using a single-ended connection Pass provides an internal circuit that can synthesize a balanced signal from a single-ended input. Enabling this circuitry is as simple as jumping pins 1 and 3 on the XLR input. In addition to the Supersymmetry technology, all the Pass Labs X Series amplifiers share the same basic power supply topology. I was told that any differences between the models are strictly based on the needs required to reach the desired output level. The X Series amplifiers also share the same two gain-stage philosophies, but once again the differences are based on the number of matched devices needed to produce the output wattage. So the majority of differences between the X150 and other X amplifiers are either cosmetic or exist as a matter of achieving the output wattage. The fundamental signal handling and amplification design level are the same.
The X150 exudes the build quality that Pass incorporates into all of their products. The rugged chassis has a stylish front plate made of brushed aluminum and the sides are lined with heat sinks. This amplifier’s shipping weight is approximately 70 pounds, so I was not surprised when it arrived that the delivery driver chose to make sure that someone was able to sign for the unit before lugging it to the door from his truck. The rear panel provides plenty of room for connecting large speaker cables and a removable power cord. Two large handles are affixed to the rear plate to help make moving the amp slightly easier. A small, but nice, feature that I like on the X150 is the remote triggering capability. Although I use spade connectors on my speaker cable, I did notice that banana plug connectors are not supported. I was told that Pass no longer includes the banana plug connector for safety reasons when exporting to countries that have electrical connections that can fit into ¾ inch banana plugs terminal. Also the X150 only has one pair of binding posts per channel and therefore does not support bi-wiring from the amp. Like the X series multi-channel amplifiers, the front panel contains a stand-by push-button switch and two LED status indicators. The Blue meter used to display the current bias of the output stage was intentionally left off to keep the chassis size smaller and make the unit more affordable. Although the meter provides the amplifier with a “cooler” look, it doesn’t provide any sonic benefit whatsoever. Nevertheless, one month after I received the X150 I learned that Pass was releasing a modified version of this amplifier, the x150.5, which is a slightly altered x150 that will include the current bias meter for an additional $500. I personally have not heard the 150.5, but the people at Pass told me that it is designed to have the same performance as the X150.
Gain: 30 db
Frequency response: -0 dB at DC, -3 dB at 100 kHz
Power Output: 150 W maximum @ 1% THD, 1kHz into 8 Ohms (300 W into 4 Ohms)
Maximum Output Voltage: +_ 50V
Maximum Output Current: +_ 20A
Input impedance: 22 kohms balanced
Slew Rate: +_ 50V/uS
Output Noise: 300 uV unweighted 20-20 kHz
Random Noise Floor: approx. 2uV
Dynamic Range: 145 db (random noise floor to peak output)