While the paragraphs below provide you with some technical information, please take a look at Pass Labs Layman Talk section for further information and comparison of this great line.

The critically acclaimed Aleph, X and XA-Series products have won numerous awards, and Founder Nelson Pass holds numerous audio patents. His achievements include developing the first dynamically biased Class A amplifier circuit, developing a fully cascode audio power amplifier, and developing the Stasis amplifier in 1977.

Nelson Pass helped popularize solid-state, single-ended Class A power amplifiers, and developed the very successful Aleph series of products, and the Super-Symmetry™ circuit, which achieves exceptionally low distortion and noise levels. The company is now poised to introduce a new generation of amplifiers and other high-performance audio products.

The newly introduced XA.5 series incorporates all the improvements of the new X.5 series and also operate pure Class A. The distortion is even lower, the control is even better.

More importantly, the XA.5 amplifiers have tremendously larger output current capacity over their corresponding XA models – more than five times the current – which is more than 25 times the power into very low impedance loads. Very difficult loudspeakers are now very appropriate loads for XA.5’s.

Sonically the result is:

Greater power and control – No matter what your loudspeaker, the X.5 and XA.5 power amplifiers have the power and stability essential to deliver the music without strain. They have the dynamic range to do justice to the 24 bit recordings of the 21st Century and the elegance to retrieve the micro dynamics offered by the most sensitive loudspeakers. This simplicity and power moves easily from total silence to explosive transients with ease and without information loss.

More music – These are not simply good high power amplifiers. They have been designed by lifelong audiophiles to deliver the warmth, sweetness, depth and space that are the hallmarks of fine audio products. Most importantly in this regard, the X.5 and XA.5 amplifiers are significant improvements on their classic predecessors.

XA models include:

• XA200.5 Mono
• XA160.5 Mono
• XA100.5 Mono
• XA60.5 Mono
• XA30.5 Stereo

See table below for comparison.

Pass Labs continues to improve its power amplifiers. After five years, these acquired enough mass to warrant a change in designation, and the X.5 series was announced. The improvements are:

Cascode JFET Symmetric front end – input differential MOSFETs have been replaced by the same JFETs we use for the input devices on our MM and MC phono stages. They have very much less noise, higher input impedance, and greater linearity. They operate self-biased in a symmetric quad topology, each device cascoded and level shifted to form the full voltage gain stage of the amplifier.

More power output devices – Greater quantities of matched complementary power Mosfets operated as followers, giving more current and power handling, and also improved linearity.

Single-ended Class A bias – The output stage not only uses a heavy bias current for push-pull Class A operation to a large portion of the rated power, but also has a single-ended bias source for single-ended Class A at low wattage.

New bias circuit – A newly developed bias generator has eliminated three sources of variation in bias current in the output stage. It also allows approximately 20% greater power output for a given supply voltage.

Improved power supplies – The power supplies have been given greater storage capacitance, larger / quieter power transformers, fast recovery rectifiers (twice as many), and improved harmonic filtering in both the primary and secondary supply circuits.

Better layout – All portions of the amplifier circuitry have been refined with respect to wiring and circuit board layout so as to achieve lower noise and distortion and greater reliability and serviceability

• X1000.5 Mono
• X600.5 Mono
• X260.5 Mono
• X350.5 Stereo
• X250.5 Stereo
• X150.5 Stereo

See table below for comparison.

The INT-150 offers the power and stability of our X.5 series amplifiers along with the refinement and convenience of our remote control operated preamplifiers, in a single compact chassis. With four RCA / two XLR inputs allowing up to 4 separate inputs selectable by remote, the INT-150 can serve as the center piece of a Hi Fi system. Powerful yet versatile, the X.5 core of the amp puts out 150 watts per channel into common 8-ohm loads, doubling its output to 300 watts per channel for more difficult 4-ohm loads. Performing on par with many expensive, complicated Hi Fi systems, the INT-150 offers high-grade performance at an affordable price, in a single beautifully constructed chassis.

The INT-150 is Pass Labs’ first integrated amplifier. Based on the X150.5 Stereo Amplifier, the INT-150 embodies the design technology and refinements- including patented Super Symmetry circuit of the X150.5 and Pass Labs’ larger X.5-Series amplifiers.

It boasts an excellent dynamic range and fast response. Designed to bridge the gap between high-end audiophile components and simple, user-friendly audio products, it moves easily from a black background to explosive transients, presenting recorded materials with sense of realism and authenticity.

Another integrated amp. A 30-watt Class A amplifier that combines the space-saving benefits of an integrated amplifier with superb performance.
Designed to bridge the gap between high-end audiophile components and simple, user friendly products, it boasts Pass Labs’ patented Super Symmetry (TM)circuit, and excellent dynamic range and fast response.

The INT-30A is rated at 30 watts-per-channel into 8 ohms, and 60 watts into 4 ohms. It boasts an excellent dynamic range and fast response. Designed to bridge the gap between high-end audiophile components and simple, user-friendly audio products, it moves easily from a black background to explosive transients, presenting recorded materials with a sense of realism and authenticity. Regardless of loudspeaker load, the INT-30A performs with stability and authority, delivering clean, expansive sound at an affordable price.

Our flagship preamplifier, this two chassis design begins with the technologies pioneered in the XP-10 and expands upon them. Tight, realistic bass is reproduced alongside the most chaotic crescendos, all within a holographic soundstage presenting instruments and voices with unprecedented spatial accuracy. The XP-20’s second chassis houses the power supply separate from the signal path, allowing for additional improvements in definition and clarity while lowering noise. A true state of the art preamplifier.

A single chassis line-stage preamplifier, the XP-10 replaces the widely respected X-1 in our product line. Featuring brand new circuit topology by noted designer Wayne Colburn, the XP-10 gives weight to highly dynamic passages, clearly and accurately reproduces bass, and allows the music to reside within a refined, balanced soundstage. An outstanding value, the XP-10 can easily be the last preamplifier you will ever need.

Since 1997 Pass Laboratories as been respected for building some of the finest phono stages in the audio industry. the transition from Aleph Ono, through X-ono and now to the XP-15 and XP-25 represents a sophistication and maturation of both thinking and component evolution.

An ultra high-quality, line-stage audio preamplifier with a unique second chassis that houses an external power supply.
It’s ideal for both moving magnet and moving coil cartridges, and presents in a new dimension in performance.

Each new design of that evolution has brought a steady improvement in measured metrics such as diminished background noise and has contributed to a sonic image presented with improved resolution and additional sonic ease.

The popular advent of the moving coil cartridge demanded all this as well as higher available gain. Each successive generation of Pass Laboratories phone-stage has addressed the special needs of these cartridges, while maintaining the ability to bring out the best in more conventional high output moving magnet cartridges as well.

The twin chassis Xp-25 eclipses the already exceptional performance of the XP-15. the Xp-25 boasts adjustable gain, two separate inputs, a low cut filter, mute feature, resistive and capacitive loading all on the front panel for easy access. With the XP-25 you will discover a whole new dimension of dynamics, inner detail and spectral richness.

In the years since the launch of our original phono preamplifier, the Xono, designer Wayne Colburn developed a number of technological advancements in the realm of phono stages, many of which are now embodied by the XP-15. Combining improved performance with a sleek, single chassis design; the XP-15 offers higher resolution, better low frequency control, and tight dynamics with an expansive soundstage and silent background. With the resurgence of high quality vinyl in recent years, there has been no better time to spin vinyl as was meant to be heard.

The single chassis XP-15 easily beats the sonioc performance of it’s predecessor the X-ono. Like some great musicians… we get requests! you spoke, we listened so you can listen better. Now, a design at the intersection of excellence and convenience.

The new SR1 is Pass Labs’ second loudspeaker, following the Rushmore, its exceptionally dynamic introductory speaker.

The new SR1, a four-way floorstanding system, is equally uncompromising. Its highly refined sound stage, deep awareness of micro-detail, and effortless dynamics deliver superb, accurate musical reproduction.

The SR1’s drivers are the best available, and employ Nextel-coated cones and a Crescendo tweeter from the renowned Seas of Norway. They present the best combination of low distortion, high dynamics, and predictable performance. It takes a minimum of four sizes of these drivers to span the SR1’s 10-octave audio range without significantly leaving the “piston” region.

The SR1 uses dual enclosures. A large bass enclosure with ten-inch and eight-inch drivers handles the bottom four octaves, and an adjustable smaller enclosure carries the midrange and the tweeter. The Seas of Norway drivers are complemented by a set of crossovers to elicit the drivers’ best performance.

Pass Labs provides great support to its customers. One way is through the information provided by Kent English of Pass Labs. The credit for all material in this page goes to Kent who is always ready to help.

Pass Labs Power Amps

Some things hold true regardless of if we are talking about listening to the X.5 (Class A/B amps) or the XA.5 (High Bias Class A amps)

Within any line there is a strong family of sound, however as the amplifiers grow in wattage they provide more of that character in a very positive sense, even when auditioned at very low wattage levels.  This ability for even the big X1000.5’s to play well at the 500mW level on for example horn loudspeakers is perhaps unique in the industry.  Pass Labs puts effort into building a product where there is a very real and self-evident sonic benefit to going up the line.

• Within either line, we have a sonic preference for mono-block amplifiers for all the reasons one might imagine.
• Mono-block amplifiers allow for greater versatility in function and physical placement.
• Mono-block amplifiers usually allow minimal length speaker cables, which maximize amplifier damping-factor, allowing for more precise speaker control.
• Mono-block amplifiers have a dedicated power supply, which minimizes channel “cross-talk” between channels.

All other things being equal mono-block amplifiers typically provide for a more refined soundstage than the equivalent multi-channel package.

X.5 OR XA.5?

In overview, the X.5 provide the greatest wattage in a given physical package.  The XA.5 deliver wattage in the most refined manner for a given package.  As for example the X350.5, X600.5 and XA160.5 share an identical physical size and similar mass.  Those otherwise similar packages at 8 ohms deliver 700 watts (2 x 350), 600 watts and 160 watts respectively.

All of the current production Pass Laboratories power amplifiers will double their rated 8-ohm wattage into 4 ohms.  However, in the current .5 line-up the XA.5 amplifiers by virtue of high current and lower voltage are the better technical and sonic choice for very low impedance loads and highly reactive loads than are the higher voltage X.5 amps.

How Hot?

All of the power amplifiers have an operational heatsink temperature of roughly 28 degrees C above ambient.  The idle current in watts represents the heat input to the environment.  Please allow at least 6 inches clearance for cooling.

What’s with the .5?

The POINT FIVE amplifiers are an evolution that takes advantage of both newer components and more than a decade of continuous design efforts that significantly enhance the original X amp design topology.  Across the board the X.5 amps (and pre-amps) are about 9 dB quieter than their ancestors and they put substantially less EMI back on the power line than our legacy product.  Without loosing anything in the way of musicality the X.5 variants provide a more accurate look back at the recordings than did the X product.  Pre .5 variants cannot be upgraded to X.5’s, due to the significant number of circuit and chassis changes

Gain?

POWER-AMPLIFIERS NORMALLY SHIP AT @ 26 dB Gain.

The amps are available from the factory at either 26 or 30 dB gain….. why?  Those with a preference for THX will demand the THX mandate of 30 dB gain from their power-amp.  Keep in mind however that at 30 dB gain a power-amplifier will clip with roughly 1.5 volts input.  With most sources supplying at least 2 volts output there will be heavy attenuation of the signal in the pre-amp at all times.

At 26 dB gain the amplifiers will clip at about the maximum output of the source component.  Long experience indicates that there are sonic benefits to less manipulation of the audio signal.

X.5 amp specifics

• X150.5, nice basic stereo amplifier, quite musical fits well into multi use systems.
• X250.5, wonderful midrange, lots of detail, nothing in the way of flaws.  Beautiful like all Pass Labs products.
• X260.5, Favorite mono-block for some, and also for the cinema customer. Slightly more detail than the other X.5 amps.  Fabulous main / center channel cinema amp.
• X350.5, more spatial detail than the X250.5, very open, workhorse stereo Class A/B
• X600.5,  Perhaps the best of the x.5 line in all respects.
• X1000.5, Darling of the big power hungry planar speaker crowd.

XA.5

• XA30.5, spectacular stereo amp with speakers above 87 dB / watt / meter sensitivity.
• XA60.5,  mono-block with greater dynamic control and better bass definition as well as more apparent bass than the XA30.5 stereo.  Excellent choice with small planar speakers.
• XA100.5,  The single largest jump in performance in the Class A series.  Rich in sonic layers, textures and minute detail.
• XA160.5,  My personal favorite power-amplifier among Pass Labs products.   All the characteristics of the XA100.5 with more “you are there” bass definition” and a greater sense of music in real space.
• XA200.5,  Pass Laboratories premiere power-amplifier, simply the best piece they know how to build in production.  Capable of driving even the most difficult load with absolute control and never calling attention to itself.

Pass Labs Pre-amps

As with the power-amplifiers Pass Labs puts effort into building product where there is a very real and self-evident sonic benefit to going up the line. With limited product in the pre-amp category these sonic gains between entry level and premiere product are quite dramatic and most notable in regression to our current entry product or our legacy product.  Pass Labs’ newer preamplifiers offer performance gains over their legacy product at a less expensive price point.

• Within the pre-amp product there is real advantage for separate power supplies, for all the reasons one might imagine
• Separate power supplies allow for twice the hardware space, more input / output choices.
• Separate power supplies allow for quieter circuits, quieter circuits provide more fine sonic detail to the listener.
• Separate power supplies allow space for a dual mono topology after the transformer, and additional regulation, which minimizes channel “cross-talk” between channels.
• All other things being equal outboard power supplies typically provide for a more refined soundstage than the equivalent single chassis package.
• All other things being equal the outboard power supplies provide additional current which enhances dynamics and low frequency nuances at all listening levels.

Circuit topology:

All Pass Laboratories pre-amplifier product operates with absolute minimal number of circuit stages.  All operate as fully balanced Class A circuits.  Noise in both halves of a balanced circuit tends to be common mode.  Common mode noise is rejected at the output of balanced circuits, providing 6 dB additional reduction of apparent noise.

As with the X.5 generation of power-amps, the current generation of Pass Laboratories pre-amps are on average 9 dB quieter than their ancestors and they put substantially less EMI back on the power line than our legacy product.  Audiophiles go to extremes to minimize power line noise, this product minimizes the need for power conditioning. Their circuits are more dynamic and more linear with greater headroom between noise floor and max output than the pervious generation.  Volume controls track each channel more accurately by a factor of 10X.  This precise channel-to-channel tracking noticeably enhances the stability and placement of stereo imaging.

XP-10 and XP-15 are clearly superior and easily demonstratable both in subjective and measured metrics to the legacy product they replace.  They provide enhanced performance and convenience at a lower price point than the product they replace.  The XP-20 and XP-25 significantly eclipse any pre-amp product this company has ever brought to market.

Pre-amp specifics

• XP-10, entry level music lovers product, more dynamic than the X1 which it has replaced.
• XP-20, reference linestage.  Dramatic gains in detail retrieval without a loss musical soul.
• XP-15, entry level phonostage, like the XP-10 notable for being more dynamic and quieter than the X-Ono it replaced at a lower cost.
• XP-25, Significant performance gains and exceptionally user friendly.  Multiple input, convenient loading and gain selection. Intuitive adjustment.  Made for our personal use, available to you.

Pass Labs Integrated Amps:

Many serious Audiophiles have not considered an integrated amplifer as worthy product for 30 + years.  Historically integrated amplifers have had somewhere between 6 and 9 gain stages.  Audiophiles instinctively know that every component, every stage, every device puts an indelable mark on the sonic signature, forever changing and degrading the music.  Though subtle the change is cummulative and ultimately destructive to the artistic intent.

The Pass Labs integrated amplifiers break the traditional integrated amp design mold.  The Pass Laboratories Integrated amplifers are two gain stage devices based on our XA30.5 and X150.5 power amps.  Input selection and a compact low noise and distortion buffered passive attenuator sit at the input of the power amp, to proved the cleanest, lowest component count and most direct signal path possible.  They provide superlative “audiophile” performance in an otherwise modest package.

Integrated specifics

INT-30A. This amplifer is the “jewell in the crown”.  It provides 30 watts into 8 ohms, 60 watts into 4 ohms and is stable into any concievable load.  It provides wattage with all the finess and delicacy that Class A operation has long been famous for.  Best with speakers of 87 dB efficieniency or greater, spectacular with difficult speaker loads such as electrostatics or planars in small systems. Wonderful, “you are there” soundstage.

INT-150. This is the companion product to the INT-30A;  The INT-150 is built from identical hardware with bias and operational points optimized for maximal wattage rather than ultimate finess.  Generally this integrated amplifier will provide greater versitility than the INT-30A with speaker loads of 86 dB efficiency or less.  The only exception would be low impedance highly reactive loads in small systems where the last  couple SPL will not be missed, such as full range electrostatics. Very dynamic amplifer at the wattage rating.

Either the INT-30A or the INT-150 are a very seductive and addictive product.  Either product provides an attractive introduction to Pass Labs and an accurate representation of the characteristics of the Class A and Class A/B product.