Product Review

Soaring Audio SLC-A300 Home Theater Stereo Power Amplifier with Audio Image Enhancement

May, 2004

Jason Victor Serinus


Click on Photo Above to See a Larger Version



● Power: 100 Watts RMS x 2 into 8
    Ohms; 150 Watts x 2 into 4 Ohms;
    Class A/B; 60 Watts Consumption
    at Idle
● MFR: 0.1 Hz - 300 kHz - 3 dB
● Noise: - 120 dB
● Weight: 38 Pounds
● Options: Balanced Input, 240 VAC,
    Rack Mount
● MSRP: $3400 USA

Soaring Audio, Inc.


It was the last day of CES 2004. To say I was feeling burned out is a gross understatement. To compound the stress of “so many exhibitors, so little time,” the fabled future spouse was in tow, and hardly in a state of bliss. So when we encountered “The Professor” walking back and forth in the Alexis Park courtyard handing out flyers posing the question “BEST SOUND OF THE SHOW?” and claiming that a number of listeners had proclaimed as much, our inner cynic geared itself up for a jolly good time. How could this upstart company dare claim to have better sound than that encountered in the Edge/Epiphany, Joule/Joseph/Elrod and Talon rooms (to name just three fine sounding rooms of many)?

Upon entering the Soaring Audio Suite, we encountered a setup dominated by huge Magnepan 3.6s. The sound, at least from where I was seated, was so sonically oversized and out of proportion that I could neither make sense of it nor fairly evaluate the amp. A visit to the second room, accompanied by “The Professor's” wife and sales manager Daniel Kolbet gave my inner cynic a huge charge when designer Professor Dr. Bill Avery's name was invoked with a titled reverence usually reserved for religious leaders.

It goes without saying that we were told that “The Professor” had carefully chosen parts (as though no one else did the same) in order to achieve an extraordinary level of sound. Unfortunately, such an extraordinary experience escaped us both in a cramped space filled with not two but at least five surround speakers. What was whispered into my ear when future spouse and I were seated alone shall not be repeated.

Nonetheless, I strive to be fair. Hence I asked for a review sample. As I was soon to discover chez Serinus, the Soaring Audio SLC-A300 sounds far better than it did in the cramped CES demo spaces. In fact, it has a hell of a lot going for it.

The Design

The amp comes supplied with one of the most user-friendly, delightfully designed manuals I have yet encountered. Each point, commented upon by the “Professor,” then receives extra commentary from the “Golden Ears” of Daniel Kolbet. Further “Bean Counter” commentary explains why certain design choices were made regardless of cost. Color printing and heavy stock paper add to the visual impact.

No regular reader of Secrets reviews is under the illusion that my technical expertise amounts to a hill of beans compared to that of other veteran members of the Secrets staff. My strong point is music, which I revere, perform, and experience live and recorded as often as possible. I therefore encourage you to examine technical discussion at the Soaring Audio website, from which I quote verbatim.

The most unique aspect of the amp's design is SA's patented SLC analog image enhancement.

SLC is claimed to provide:

“Acoustic Restoration: smooths [sic] out digital grit. Digital to Analog converters send out a voltage that is read from a CD or DVD at 44,100 or 48,000 voltage samples each second. The SLC ‘smooths [sic] across' these discontinuities and gives the impression of having a higher sampling rate. In surround sound it brings out details that are lost because of the compression in 5.1 formats.

“Enhanced imaging: left and right enhanced outputs combine to form a solid phantom center channel that is wide and deep.

“Dynamic detailing: increases the perceptual dynamic range, at any output level.

“In video images, the apparent sharpness of a picture can be increased by employing a technique called edge enhancement. The impression to the human eye is that the focus has been sharpened and more detail is visible. In an analogous way, by adding a tiny emphasis to certain details in the waveform, the impression to the human ear is that the details of the sound stage are more clearly perceived.”

The SLC-A300 can be fed a signal directly from a CD player or processor. If the signal is high enough, no preamp is needed.

The front of the amp offers an on/off button, a light that shows when the amp is on, and a master volume control knob toward the right side.

In addition, there are two enhancement level control knobs on the left front, one for each channel. These are adjusted with the help of four LEDs per channel.

Green Lights, Red Lights

The input pair of LEDs on the left reflects the level of the RCA inputs. The input level is adjusted by adjusting the output level of the preamp or source device.

The output pair of LEDs on the right reflects the amount of signal enhancement. The amp's output level is adjusted by turning the two enhancement level control knobs.

Input Green indicates presence of normal signal level for optimum enhancement. If the Green Input light does not come on, the input signal can be adjusted by balancing the preamp or source's output level with the amp's input level. This necessitates both adjusting the source output level and also turning the amp's master volume levels and corresponding enhancement volume level knobs up and down. It may take a few minutes to get a feel for, but it's easy to do.

Input Red indicates that the maximum level (5 volts RMS) for which the input was designed has been reached. Clipping occurs just above this point. To avoid clipping, the input green light should flash without ever activating the red. It may take awhile to get there. The big challenge is getting it right with wide dynamic recordings, such as Reference Recordings' Rachmaninoff Symphonic Dances. I personally found it challenging to get the green lights to come on in soft passages without the red lights beaming away in loud passages. Better to have the green lights come on occasionally, I shortly discovered.

Output Green indicates good enhancement to the signal. Output red should normally not come on, since it indicates that the maximum design level of enhancement has been reached and clipping is imminent.

Welcome to the SLC-300A light show. At any moment, four green lights and occasional no-no red lights may flash away as music plays. Yes, Virginia, there is a Santa Claus.

The lights are small and not overly bright, thank goodness. Nonetheless, the visual experience does seem reminiscent of those mass-market receivers of old, complete with all kinds of illuminated bells and whistles that make everything appear far more technically complex than necessary. Such flashing light features were dropped when designers discovered that they fascinated many men (not this one) but drove women away in droves.

Of course, the difference between the flashing lights of the ‘80s and those on the Soaring Audio is that the latter are necessary for optimal adjustment. They are intended, not to impress, but to enhance.

The rear panel consists of an IEC connector for a removable power cable, one set of single-ended audio inputs, and one set of speaker wire outputs that accommodates spade lug terminations. High quality Cardas speaker connectors are employed. There are also major size heat sinks, preferable to the noise of a fan.

Initial Impressions and System Transformation

Soon after connecting the amp for the first time, I called Bill Avery to further understand how to best evaluate the signal enhancement feature. He suggested I first listen flat, with the Theta DAC/preamp's volume turned up, the amp's left SLC knobs turned off, and the amp's right master volume control turned up as far as possible.

This produced no sound whatsoever. I found that I had to add enough signal enhancement to achieve listenable levels. I therefore kept preamp and main volume levels very high, turning SLC controls up only as far as necessary to achieve desired volume level. No green lights flashed as a result.

Shortly after my first listening session, we moved to our new home. Sound chez Bellecci-Serinus is a whole different experience.

Chez Serinus' spongy top-level apartment wooden floor has been replaced by a ground-level, well-supported wooden floor. The result is much firmer bass, with bass pitch far more well-defined.

The ceilings are now 9'2” high rather than 8.5'. Speakers are farther from the back wall and farther apart, with the listening room depth close to 24 feet. I sit much closer than that, but there is ample room behind me. Even more important, an additional 12-15 feet of open space extends on either side of the speakers. My Talon Khorus X speakers finally have room to breathe.

As for my power, there is an equally major difference. Instead of compromised, ancient 14- and 12-gauge wiring running the length of three floors and two fuse boxes, I'm listening via brand new 10-gauge wiring on a dedicated 30-amp line. In place of a grounding wire to a cold water pipe, I've got an actual grounding rod driven into the earth. As before, wiring leads directly into a PS Audio Ultimate Outlet which is connected to the P600 Power Plant by means of an Elrod EPS-3 Signature power cable. Though I still have some fine room tuning to do, the sound of my reference system in this new space, complete with the Theta Generation VIII DAC/preamp, is eminently musical, frequently approaching the magical. It's far more live, satisfying and boundless than before.

With and Without SLC

My reactions to the amp without SLC were lukewarm. Auditioning the stereo layer of Michael Tilson Thomas' new multi-layer surround sound SACD of Mahler's Fourth Symphony (SFS Media) was a case in point. I found the strings a little wiry, lacking the smoothness I heard during the symphony's actual live performance or on other high-resolution SFS recordings. Horns blared a bit, and cymbals sounded clattery. I also found the midrange lacking in richness. On the other hand, bass seemed even more impressive than with my Jadis Defy 7. Such perceptions were reinforced as I listened to a number of the discs chosen for audition.

Then I fully engaged SLC enhancement. This was accomplished by first turning the master volume all the way off, turning the SLC knobs up to 12 o'clock and beyond, and finally adjusting the balance between all volume controls on Theta and Soaring Audio. It took awhile to get it right. But once I did, I only had to make minimal readjustment for other recordings.

Engaging SLC radically changed the sound. In Soaring Audio terminology, I had created a “Phantom Center Channel” Though I heard no more phantom center channel than with any other excellent stereo amp I've auditioned, SLC definitely fleshed out the sound. The midrange seemed far fuller, the highs smoother and easy on the ear if at times a bit damped.

When my extended listening had concluded, there was no question in my mind that taking advantage of SLC, regardless of the fact that it enhances signal by slightly adding reverb and boosting certain frequencies, provides a very satisfying listening experience.

Going Deeper

My usual caveat applies here. My reference amp, the Jadis Defy 7, would cost at least three times more than the Soaring Audio SLC-A300 by today's standards. It is also a tube product, with all the advantages and disadvantages thereof. For those who have not seen the superb dialogue between Harry Pearson, Robert Harley, Jonathan Valin and Paul Seydor on the sonic differences between tube and solid state, I highly recommend it. My experience confirms theirs.

Knowing that Secrets readers love different kinds of music, I chose seven recordings total. Two were full symphonic spectaculars, Reference Recordings' "Rachmaninoff Symphonic Dances" and MTT's "Mahler Symphony No. 4". Others included Hilary Hahn's "Brahms' Violin Concerto"; Benny Carter and Rosa Passos' great bossa nova disc on Chesky; an early disc from jazz vocalist Diana Kraal; Terry Evans singing the blues on a recording I've mentioned more times than there are stars in the sky, and soprano Karina Gauvin singing Canteloube's "Songs of the Auvergne" with chamber accompaniment.

The first thing that struck me about the A300 with SLC engaged was the fullness of its sound. This is a powerful amp. The bass is deeply extended, the midrange quite full. I especially checked out the final double bass conclusion to Mahler's Symphony No. 4, the drums in the second song on the Auvergne disc, and Ron Carter's bass. In all cases, I heard more pronounced bass from the SLC-A300 than from the Jadis. A definite plus.

At the same time, I missed the beauty of highs and continuity of tone I hear from the Jadis. Despite claims of an extremely low noise floor, I experienced less transparency from the Soaring Audio than from the Jadis. The “blacker black” we audiophiles long for was not quite there. The mesmerizing liquid transparency I hear on the Audioquest/JVC-XRCD "Terry Evans Puttin it Down" was also absent. Highs did not ideally shimmer and glisten, distinct three-dimensional layers of sound and textures did not emerge.

David commented that on the Songs of the Auvergne, Karina Gauvin's voice seemed more removed than he was used to hearing. “There doesn't seem to be a foreground; she seems almost behind the instruments.” I heard this as a lack of depth between voice and instruments made more apparent by less transparency, clarity, and high extension than I hear with the Jadis.

I also failed to hear the same realistic quality to the triangle that I usually hear on Rachmaninoff's Symphonic Dances. It seemed flatter, with less resonance and decay. I also heard less reverb around the voices of Diana Kraal, Rosa Passos, and Terry Evans. David commented that while engaging SLC made the sound more full, it also made Terry Evans sound more removed and filtered than before. “More transistor-like” became his most commonly uttered commentary on the difference between the two amps.

But remember. Please remember. I am not only talking about the differences between tube and solid state, but also about amps in entirely different price categories. My sonic recollections of solid state amps in the Soaring Audio's price range leads me to conclude that it is quite an excellent performer. It certainly has a better tonal balance and a far fuller fuller midrange than the upgraded McCormack DNAs I've heard in my own system and at two other friends' homes.

On the Bench (JEJ)

THD at 1 kHz and 5 volts output into 8 Ohms measured a little higher than we usually see, but this could be a result of low negative feedback or other design implementation.

IMD was very low, using 1 kHz and 1.5 kHz sine wave input signals. THD was relatively high, comparatively speaking.

With 5 kHz and 6 kHz input signals, again, IMD was low, but THD was high, comparatively.

At 10 kHz, THD was approaching 1% at 5 volts output into 8 Ohms.

Frequency response was  0.5 dB from 20 Hz to 96 kHz, which is excellent.


For those drawn to the solid bass and full presentation of solid-state products, the Soaring Audio SLC-A300 is highly competitive with other amps in its price range. Some consider it amongst the best products released in the past year. With its unique SLC engaged, this amp will bring much pleasure to listeners. Most definitely deserving of an audition.

- Jason Victor Serinus -

Associated Equipment:

Digital Front End
Sony 707ES transport modified by Alexander Peychev of APL Hi-Fi
Theta Gen VIII DAC/Preamp

Jadis Defy 7 Mk IV modified with a Siltech silver harness

Talon Khorus X speakers (with latest modifications and Bybee filters that render its response even across the spectrum and greatly improve the bass)

Nordost Valhalla single-ended interconnects and balanced digital interconnects
Nordost Valhalla bi-wired speaker cable
Acoustic Zen Silver Reference II balanced interconnects
Powercables: Elrod EPS-1, 2, and 3 and EPS-2 and -3 Signature on main chain plus Harmonic Tech, Nordost, and AudioPrism SuperNatural S2 elsewhere

PS Audio P600 Power Plant power synthesizer with MultiWave II
PS Audio Ultimate Outlet; PS Audio Power Ports
Michael Green Deluxe Ultrarack, Basic Racks and room treatment,
Michael Green Audiopoints, Ganymede supports. Marigo supports and Black Diamond Racing Cones
Shakti stones
Bedini Quadra Beam Ultraclarifier
Audioprism Stoplight
Marigo Stealth Mat for CDs
Ayre demagnetizing/break-in disc


© Copyright 2004 Secrets of Home Theater & High Fidelity

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