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Over the course of his 30-plus years in high-end audio, Nelson Pass's designs have never been far from the leading edge. In his first Threshold amplifiers he pioneered the use of dynamically adjusting bias and cascode circuitry; then, in the later Stasis models, he switched gears to the simpler approach of pure class-A. All were innovative designs, and among the very best-sounding amps of their time, but were just warmups for what was to come. In 1991, Pass Labs introduced the Aleph 0, a class-A amplifier that was a startling departure from conventional solid-state designs and combined design…
My system was pretty stable during the XA30.5's tenure here. I used two turntable-tonearm combos: the VPI HR-X, and a Spiral Groove SG-2 with a Triplanar arm, each fitted with either a Grado Statement Reference or Lyra Titan i cartridge. Digital signals were supplied by a Primare CD31 CD player, and the electronics consisted of a Sutherland PhD phono stage feeding either a Sutherland Direct or Placette Active line stage. The Pass drove two sets of speakers, the Sonics by Joachim Gerhard Allegras and my Wilson Audio Sophia 2s. After experimenting a bit, I settled on Nordost Valhalla…
Sidebar 1: Specifications
Description: Solid-state stereo power amplifier. Inputs: 1 pair unbalanced (RCA), 1 pair balanced (XLR). Outputs: 2 pairs binding posts. Rated power output: 30W into 8 ohms, 60W into 4 ohms (both 14.8dBW). Maximum output voltage: ±35V. Maximum output current: ±20A. Voltage gain: 26dB. Input sensitivity: 0.77V at 26dB gain. Frequency response: 1.5Hz–100kHz, –3dB at 1.5Hz, –2dB at 100kHz. Signal/noise: 150dB at full power. Distortion: 0.01% at 3W, 0.1% at 30W. Input impedance: 30k ohms balanced, 15k ohms unbalanced. Damping factor: 150 at 8 ohms. Slew rate: ±50V/…
Sidebar 2: Associated Components
Analog Sources: VPI TNT HR-X turntable & tonearm; Spiral Groove SG-2 turntable, Triplanar tonearm; Lyra Titan i, Grado Statement Reference cartridges.
Digital Source: Primare CD31 CD player.
Preamplification: Sutherland PhD phono stage; Sutherland Direct, Placette Active line stages.
Power Amplifiers: Mark Levinson No.20.6, VTL Ichiban (both monoblocks).
Loudspeakers: 804NHT SuperZero, Sonics by Joachim Gerhard Allegra & Anima, Wilson Audio Specialties Sophia 2.
Cables: Nordost Valhalla, Stereovox, Audience Au24, Nirvana S-X Ltd.…
Sidebar 4: Measurements
I examined the Pass Labs XA30.5's measured behavior with Stereophile's loaner sample of the top-of-the-line Audio Precision SYS2722 system (see the January 2008 "As We See It" and www.ap.com); for some tests, I also used my vintage Audio Precision System One Dual Domain.
Before performing any tests on an amplifier, I run it for 60 minutes at one-third its specified power into 8 ohms, which is thermally the worst case for an amplifier with a class-B or -AB output stage. Superficially, the XA30.5 appears to be a 30Wpc class-A design. But this is not the…
Erick Lichte wrote about the Pass XA30.5 in August 2009 (Vol.32 No.8):
Have you ever dated a girl and then, six months into the relationship, met her superhot younger sister? That pretty much sums up my long-term romance with my old Pass Labs Aleph 3 power amplifier ($2300 when available but long discontinued), and my flirtatious liaison with the übersexy Pass Labs XA30.5 ($5500).
Knowing that I owned an Aleph 3, John Atkinson pimped out an XA30.5 to me so that I might compare the two. I jumped at the chance—I love my Aleph 3 (footnote 1) and wanted to see how Nelson Pass's design…
When I reviewed the Moon Evolution P-7 preamplifier ($6900) from Canadian manufacturer Simaudio in March 2009, I was impressed by the qualities of both the audio engineering and the sound. It was a no-brainer, therefore, to follow that report with a review of the matching power amplifier, the Moon Evolution W-7. In March 2006 Kalman Rubinson reviewed Simaudio's Moon Evolution W-8, which offered at least 250Wpc into 8 ohms (I measured 310Wpc at clipping). The W-7 looks identical to the W-8, but is 10 lbs lighter, offers 150Wpc into 8 ohms, and retails for $8900 compared with the W-8's $13,500…
Sidebar 1: Specifications
Description: Solid-state, dual-mono stereo power amplifier. Inputs: 1 pair unbalanced (RCA), 1 pair balanced (XLR). Outputs: 1 pair WBT binding posts. Comms: RS-232 port, 12V trigger input and output. Rated power output: 150W into 8 ohms, 300W into 4 ohms, 600W into 2 ohms (all 21.75dBW). Maximum output voltage: 34V. Maximum output current: 42A peak, 18A continuous. Voltage gain: 31dB. Input impedance: 47.5k ohms. Input sensitivity: 980mV for rated power. Frequency response: 10Hz–200kHz, –3dB. Channel separation: 105dB at 1kHz. Output impedance: 0.01 ohm. Signal…
Sidebar 2: Associated Equipment
Digital Sources: Meridian 808i.2 CD player/preamplifier, Ayre C-5xe universal player; Benchmark DAC1, Bel Canto e.One DAC3 D/A converters; Bel Canto USB Link 24/96, dCS 972 digital format converters; Logitech (Slim Devices) Transporter network music player with Apple Mac mini running OSX for media storage.
Preamplifiers: Simaudio Moon Evolution P-7, Parasound Halo JC 2.
Power Amplifiers: Musical Fidelity 750K Supercharger monoblocks, Pass Labs XA30.5.
Loudspeakers: Revel Ultima Salon2.
Cables: Digital: Kimber Illuminations Orchid AES/EBU,…
Sidebar 3: Measurements
I used the top-of-the-line Audio Precision SYS2722 system (see the January 2008 "As We See It" and www.ap.com) to assess the Simaudio Moon Evolution W-7's measured behavior; for some tests, I also used my vintage Audio Precision System One Dual Domain.
Before performing any tests on an amplifier, I run it for 60 minutes at one-third its specified power into 8 ohms, which is thermally the worst case for an amplifier with a class-B or -AB output stage. The W-7's heatsinks were around 55°C (131°F) at the end of the period; the THD in the amplifier's outputs…