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PS Audio GCA-250 Dual Mono Hybrid Analog/Digital Switching Power Amplifier

Part I

October, 2005

Jason Victor Serinus

 

Specifications:

● Two-Channels; 250 Watts per
    Channel into 8 Ohms; 500 Watts
    per Channel into 4 Ohms
● THD: 0.02%
● Sensitivity: 2.00 Volts RMS
● MFR: 10 Hz - 20 kHz
0.1 dB
● Single-Ended and Balanced Inputs
● Dimensions: 4" H x 17.25" W x 14" D
● Weight: 27 Pounds
● MSRP: $2,995 USA

 

PS Audio

www.psaudio.com

Introduction

PS Audio is one of the more respected names in the audiophile arena. Even a cursory inventory of equipment owned by longtime Bay Area audiophiles turns up a 15-year old PS Audio preamp in one home (still used in the downstairs system), and an early, much loved amp in another. I continue to use and admire the P600 Power Plant, whose original P300 precursor received one publication's coveted "Product of the Year" award back in 2000. I also use the PS Audio Ultimate Outlet and Power Port wall outlets.

In a design field populated by an unholy conglomeration of music lovers, hustlers, eccentrics, undisputed geniuses, anti-social geeks, egomaniacs, visionaries, and pretenders to the throne, Paul McGowan stands out as one of the most likeable and respectable of the lot.

The man clearly loves enriching people's lives with music as much as he enjoys interacting with them. I have always found PS Audio's customer service department a joy to work with, and Paul himself readily accessible and willing to assist. Anyone who owns PS Audio gear and has found their system suddenly on the blink a week before that long awaited guest is finally scheduled to come over for a first listen will find themselves grateful for the attention the company will pay to their plight.

When I approached Paul at CES 2005 about reviewing one of his new amps, he knew full well that I in general prefer the sound of tubes over that of solid state. He nonetheless expressed confidence in the sound of his new GCA-250, the 250W model in PS Audio's line of three GCA gain cell amplifiers with power ratings of 100, 250, and 500W. The amp arrived some months back, and has sat in cue for awhile as I've slowly moved through the backlog of equipment awaiting review.

The GCA-250 is a dual mono, class D (digital switching) amplifier. With one pair of single-ended RCA inputs, one pair balanced XLR inputs, and work-like-a-dream-PS Audio locking speaker binding posts, the marketing info touts many benefits. These include, besides PS Audio's Gain Cell technology, little or no heat a MAJOR factor in tight quarters where the heat of tube equipment makes listening uncomfortable if not downright impossible in the warmer months extremely low noise, rock solid image, deep bass, open and spacious sound, ultra low distortion, and effortless performance with "any" loudspeaker. On paper, at least, the GCA sounds like one of the better buys in high-end audio.

PS Audio offers a 30-day in-home trial with a full refund minus shipping.

Their transferable warranty covers five years if the warranty card is returned within 90 days of purchase; otherwise, three years, with an additional two-year extension for $50. To qualify for the extended warranty, you must purchase from an authorized dealer and submit a written receipt.

The Inner Workings

PS Audio has achieved fame in my book for the simplicity of its online technical discussions. Rather than regurgitate it all, I shall concentrate on a few points, and invite you to check out the rest by clicking on a host of links listed at http://www.psaudio.com/products/gca_amplifiers.asp.

First, this is a true dual mono design. Based on PS Audio's new Gain Cell technology each GCA contains two completely independent gain cells and two equally independent mono SDAT power modules. Only the power cable is shared.

Second, the GCA series couples analog Gain Cell Technology at the input stage to its SDAT (Super Digital Amplifier Technology) Class-D power output stage. It uses "a fully independent and regulated switching power supply to feed each of the power modules, virtually eliminating any need for input power transformers and heavy magnetics." MOSFET transistors inside the analog power module operate upwards of 85% efficiency.

Note that the GCA is a hybrid design. While someone who reviewed a product in the company's GCC series for another website seems to have inferred that the amp's input stage is analog and the output stage is digital, that is not actually the case. The information on the PS Audio website is a little confusing, so I wrote to Paul McGowan for an explanation, and he sent the following response:

"The GCA-250 is a hybrid product in the sense that the input stage is pure class A analog Gain Cell and the output stage is a class D switching power amplifier. Hybrid because it's two distinctly different technologies married into one.

"When I switch back and forth with the usage of a digital output stage and an all-analog output stage I use the term 'digital' because people are used to the term and it helps them relate to what we're doing. Strictly speaking, it's not a digital stage; in fact, it's all analog.

"Pulse width modulation [PWM] switches the output transistors on and off in varying lengths of time thus the use of the term 'digital' because the output stage is a series of on and offs. However, in reality, a true digital system incorporates some type of coding scheme of ons and offs that are later interpreted by a computer-like device and then converted to analog.

"Not so with PWM. The varying ons and offs are converted directly to analog with a simple filter that rolls off the transitions. This is possible because it's a 100% analog system to start with."

PS Audio touts their gain cell as "about the most perfect gain block ever invented." Called the "heart and soul" of every GCA product, a gain cell is "a single block of analog gain in a potted module, direct coupled from input to output in one of the cleanest, purest audio paths ever devised."

Gain Cell specifications include:

>80dB input common mode rejection

>0.005% THD+N @1 volt rms

>-100dB SN A weighted

Gain adjustable from -100dB to +30dB

Step resolution >0.001dB

Input impedance 47 kOhms for both +/- inputs

Output impedance 100 Ohms for both +/- outputs (Note: This is the impedance for the Gain Cell output connections, not the output impedance at the speaker terminals.)

Boasting perfect linearity, with the same voltage in and out, PS Audio claims "effortless sound regardless of volume. From micro dynamics to macro dynamics, this amplifier sounds the same on the softest passages to the loudest orchestral crescendos."

Please read on to discover how this translates into sound quality.

Set-Up

I replaced my reference Jadis with the GCA-250. Noting that the manual affirms that the amplifier can benefit from "aftermarket isolation devices such as cones, spikes, and Sorbothane pads," I chose Ganymede ball bearing supports, which to my ears provide far more vibration isolation without damping highs than other supports I've tried.

Again noting that PS Audio's own words, "While the supplied power cable is adequate for the task it is not going to provide the best performance" reflect my own experience, I installed my reference Nordost Valhalla power cable. In my experience, the Valhalla allows components to achieve far more of their full potential than the single PS Audio xStream Power cable I have tried.

PS Audio recommends the use of power conditioning equipment "such as a PS Audio Power Plant, UPC-200, or any of the Ultimate Outlet or Power director series from PS." They do not recommend other AC filter power conditioners, claiming, "Most of these will 'bleach' the sound and rob the music or video soundtrack of life and dynamics. If you do not us PS Audio Power Conditioning equipment, you would be advised to plug the GCA Power amplifier directly into the AC wall receptacle."

No problem. I wouldn't even think of plugging the amp directly into the wall, knowing the sonic compromises I've experienced when doing so. Given how little current the GCA-250 draws, plugging it into the P600 Power Plant was a piece of cake.

Interconnects and speaker cable were also Nordost Valhalla. The preamp was my reference Theta Gen. VIII DAC/preamp, whose specs seem totally compatible with the GCA-250s.

At first I tried the amp's single-ended inputs. Then, switching to the balanced XLRs, and adjusting the simple input switch on the back of the amp accordingly, I confirmed PS Audio's assertion that "a balanced XLR type of output allows the lowest noise connection between preamp and power amp, and allows owners to take advantage of the high common mode rejection characteristics found in the Gain Cell of the GCA Series Power Amplifier. Be sure to use a high quality well shielded and well regarded interconnect for this critical link."

I stuck with balanced inputs for the duration of my listening experience.

I also kept the amp powered on throughout the five to six weeks I spent auditioning it. The company claims that keeping the amp on insures that its internal AC capacitors stay working properly, draws a negligible 40 W current (well, more like 65 through the inefficient Power Plant), and does not shorten lifespan. Since the amp really does produce little heat, and the intensity of the front panel's electric blue logo can be set to medium or shut off entirely, I found keeping it on relatively painless.
 

Click Here to Go to Part II.

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