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POSITIVE FEEDBACK ONLINE - ISSUE 13
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soaring audio

SLC-A300 amplifier

as reviewed by Fown-Ming Tien, Ed Morawski, and Greg Ewing

 

 

 

 

FOWN-MING TIEN'S SYSTEM:

LOUDSPEAKERS
Onix Reference 1 monitors on Osiris 24.5" stands with an Onix UFW-10 subwoofer.

ELECTRONICS
Aragon Aurum preamplifier and Aragon Palladium II monoblock amplifiers.

SOURCES
Audio Alchemy DDS-Pro CD Transport, Perpetual Technologies P-1/A Upsampler/Interpolator, Perpetual Technologies P-3/A DAC w/ModWright Level 2 mods stacked on PandaFeet sorbothane vibration dampers.

CABLES
Onix Statement speaker cable, Argent Jaden Signature RCA interconnect, Acoustic Zen Silver Reference MkII RCA interconnect, Onix Grand Master Digital Coax from CD-T to P-1/A, Revelation Audio Prophecy I2S cable connecting P-1/A to P-3/A, Onix Statement power cord, Onix Statement 1 power cord, two Absolute Power cords used on the amplifiers.

ACCESSORIES
Quantum Symphony Pro and Quantum ElectroClears.

 

I was thrilled when PFO Editor Dave Clark told me that I was now part of the review staff. He immediately gave me some power cords and the Soaring Audio SLC-A300 stereo amplifier to review, but that was before I found out that I would be moving within three weeks due to a job transfer. Suddenly, reviewing audio gear seemed to be just another deadline among the many rushing at me like a freight train. Fortunately, the PFO deadline was the most enjoyable of the ones I needed to meet, so I chose to attack it first. Reviewing is a dirty job, but someone's got to do it!

I first heard the Soaring Audio SLC-A300 amplifier at CES 2004. SLC stands for Signal Loss Compensator, which is supposed to provide image enhancement, smooth out the digital grit sent out by digital-to-analog converters, and increase the amplifier‘s dynamic range at all output levels. I felt that the amp presented movie soundtrack material in a less digital fashion, but could not be certain, as the room and associated equipment were unfamiliar.

Because the amplifier is less than 3.5 inches high, its 38-pound weight was rather surprising. The SLC-A300 features oxygen-free copper Cardas speaker connectors, an oversized transformer, Mogami internal wiring, and massive heat sinks to eliminate the use of a cooling fan. The back panel has inputs for left and right channels, an IEC input for a power cord, connections for a 12V DC remote trigger, and the speaker connectors. The front panel is rather unconventional. Two knobs on the left side control the Signal Loss Compensator feature. To the left of each knob are LEDs. The input pair indicates the signal level from the RCA inputs, one green and one red. Green signifies that a signal is present, and red comes on when the amp has clipped. The output LEDs reflect the amount of enhancement applied by the SLC. A volume knob and power switch are on the right side of the amp's front panel.

Since the amp had a gain control, I tried connecting my source directly to it, but found that I preferred the sound with my preamp in the circuit. After spending some time fiddling around with the SLC and gain controls on the amp, I discovered that the best sound was achieved with the SLC knob set at the 2 o'clock position and gain knob at 11 o'clock. Having found these settings, I discovered that the SLC-A300 was extremely quiet. I had never found the noise level of my Aragon Palladium II monoblocks to be objectionable, but in comparison to the dead silence of the SLC-A300, the Aragons were positively noisy. It is important to note that this lower noise floor was only achieved after I had adjusted the SLC-A300's settings. Prior to dialing these in, I experienced high levels of hiss at idle.

I then proceeded to do some critical listening. The first thing that became obvious was excellent imaging, an increase in midrange detail, and a forward presentation on Andrea Bocelli's Cieli di Toscana and Josh Groban's self-titled album. The excellent texture, tonality, and detail of both recordings revealed the weaknesses and strengths in the amplifier's midrange. The vibrato from both singers was simply the most detailed I had ever heard. Imaging was tight and focused, and had excellent clarity with no haze or smearing. A quick return to the Aragon amps confirmed these impressions. The SLC-A300's midrange was more forward and detailed, but added no harshness. With the Aragons, the singers seemed to take a step backward, and while their voices were not lacking in vibrato, there was less of it. I have always found the midrange of the Palladium IIs to be one of their strengths. They are supremely smooth, yet maintain excellent fullness, detail, warmth, and balance compared to other amplifiers I have heard, so I was surprised to find an amplifier that could surpass them in this respect without an increase in grain or glare. Piano notes had no hint of the iciness or hardness that less capable amps can impart.

My Palladium amplifiers are absolutely incredible when it comes to bass reproduction. They produce the most articulate, detailed, and well-controlled bass of all the amps I have owned. Looking at the SLC-A300's specifications of 100 watts at 8 ohms and 150 watts at 4 ohms, I had doubts about its ability to control bass. This is not what I consider a powerhouse of an amp, especially compared to the Palladiums, which are capable of delivering 400 wpc at 8 ohms and 1000 wpc at 1 ohm. To test my theory, I played Bela Fleck's Flight of the Cosmic Hippo, a disc that will reveal an amplifier's ability to dish out tight, clean bass. While the Soaring Audio amp performed admirably for a 100-watt amp, it fell far short of the bar set by the Aragons. Instead of the vise-like grip that I have become accustomed to, the bass sounded muddy and lacking in impact and punch. The lack of fullness, depth, and articulation resulted in a rather flat presentation. I would never expect a 100-watt stereo amplifier to be able to surpass or even match a pair of 400-watt monoblocks, but in the realm of 100-watt amplifiers, the SLC-A300's bass performance was admirable, with power reserves deep enough that even the extremely demanding cannon blasts on Seiji Ozawa's EMI recording of Tchaikovsky's 1812 Overture did not leave the amp gasping for breath. It failed to clip, even pumping out more than 95dB.

The SLC-A300's treble, airiness, and transparency were excellent, due to its forward nature. On the Bela Fleck disc, brushes, high hats, cymbals, and snares had an openness that I have not experienced with my amplifiers. Nevertheless, accompanying the additional airiness was a bit of extra sibilance. The "S" sounds of voices were accentuated, although not to levels that I considered objectionable. I enjoy a detailed, yet smooth treble presentation with as little sibilance and brightness as possible. With the SLC-A300, the higher trumpet notes on Miles Davis' Kind of Blue were a bit more piercing than I prefer. Of course, I am accustomed to the very smooth top end of the Aragon amps, and it is possible that spending additional time with the SLC-A300 would allow my ears to adjust to the sibilance.

My digital front end is relatively glare-free, so I did not notice whether the Signal Loss Compensator smoothed out digital grit in my system, but I did notice an extremely wide and deep soundstage. When pushed to play at high levels, the SLC-A300 remained composed, and never sounded strained or compressed. The only area in which I found myself desiring higher performance and more refinement was in the amplifier's bass reproduction, and the only area in which I found myself desiring less was in the level of sibilance. The strength of the Soaring Audio amplifier was in the wonderful midrange, which was very engaging and full. Fown-Ming Tien

 

 

 

ED MORAWSKI'S SYSTEM:

LOUDSPEAKERS
DIY 2 way monitor speakers with Scanspeak 8535 & 9700 drivers.

ELECTRONICS
Plinius SA-102 amplifier and an E.A.R. 864 preamplifier.

SOURCE
Musical Fidelity Nu Vista 3D CD player, Aries turntable w/JWM 10 arm and a Dynavector 20X cartridge.

CABLES
Analysis Plus Oval 9 Speaker cables, Cardas XLR, Kimber Camble XLR, and Holophonic-PC interconnects, power cords.

ACCESSORIES
Dedicated balanced power with Brick Wall Surge Supression.

 

Despite spending two weeks listening to it, I simply could not get a handle on the Soaring Audio SLC-A300. Although it is billed as a home theater amp, it is only a two-channel amp, so I listened to it in a music system. The oddities of this piece of equipment are many. It is only 3 inches high and 19 inches wide, but at 38 pounds, it is extremely heavy for its size. The first things I noticed were all the LEDs and knobs. These are a departure for a power amp, but they are required because of the SLC-A300's Signal Loss Compensator (SLC) circuitry. This was one of the most confusing aspects of the amplifier, and one reason that Soaring Audio includes rather extensive "quick setup" instructions in the manual.

The manual states that the SLC-A300 should be directly connected to the source. I took this to mean that this was optional, especially since this is supposed to be a HT amp, and would therefore need to be connected to a pre/processor. At any rate, I could not get it to function properly with any preamp. I first tried my E.A.R. 864, but the volume was too low. I tried a Harmon Kardon HT receiver, with the same result, then a Panasonic and a Kenwood—no luck. With every unit, the volume was extremely low, even with the SLC controls turned up to maximum. The manual states that the SLC controls should be adjusted to bring the green LEDs on almost continuously, but I was not able to do this with any preamp or receiver. I was about to give up, but decided to try hooking my Musical Fidelity Nuvista CD player directly into the amp. Low and behold, sound! I was even able to make all the adjustments called for in the manual. I cannot explain this, but I figured okay, now I can review the unit.

The SLC-A300 is rated at 100 watts into 8 ohms, and that sounded about right. The bass was strong and well defined. The soundstage and imaging were wide and also well defined. I really could define the character of the unit. I had the Xindak integrated amplifier in the house at the same time for comparison. I thought the Xindak was sterile, but the Soaring Audio was simply neutral. It did not impart anything to the music, nor did it take anything away. According to the Soaring Audio website, the SLC circuit is supposed to take out the digital "grit":

Acoustic Restoration smooths 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 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.

This lead me to wonder whether the SLC circuit only worked with DVD players, so I tried a Pioneer 525 DVD player with a music CD and heard no improvement. In my opinion, DVD players make terrible CD playback devices, and the SCL-A300 did not make me change my mind. After switching back to the Musical Fidelity CD player, I played many CDs and fiddled with the SLC controls, but again couldn't hear any difference. The SLC-A300 seemed competent, robust, and fairly enjoyable to listen to. It didn't seem to color the music in any way. It sounded fairly grain-free, but the Musical Fidelity Nuvista has always sounded that way, so I'm not sure the SLC-A300 had anything to do with it. I did miss my E.A.R. tube preamp when it wasn't in the chain, and perhaps that is why I was not moved by the amp.

I am not sure where this piece of equipment is supposed to fit in the scheme of things. I also do not understand the thinking behind including SLC circuitry on an HT amp that is going to be getting a signal that has already been processed to death. And if it doesn't work with pre/processors, what is the use of it? If you are looking for a two-channel power amp that you can run without a preamp, this might fit the bill. Ed Morawski

 

 

 

GREG EWING'S SYSTEM

LOUDSPEAKERS
Magnepan 1.6QRs, 1 12" Titanic II spiked and sealed subwoofer.

ELECTRONICS
Parasound HCA-1500 amp, Harmon Kardon HK-3475 preamp/tuner, Hypex HS200 200W subwoofer amplifier, Stax headphone amp and phones.

SOURCES
Sony SCD-222ES SACD CD player modified with LC Audio LClock and Black Gate capacitors.

CABLES
Kimber speaker cables, Kimber and Canare Star Quad interconnects.

ACCESSORIES
Taddeo Digital Antidote II, Bright Star Audio IsoNodes, Audio Prism QuietLines, Auric Illuminator, lots of ferrite rings.

 

What is "Signal Loss Compensation"? We may never really know. The folks at Soaring Audio have patented it, so they must have disclosed the details of the circuitry, yet on their website they describe what SLC sounds like without saying anything about how it alters the signal. Given widespread audiophile paranoia, this is probably a good thing, but if it brings me closer to my favorite music I am all for it. Having recently acquired the Margules Magenta ADE-24, I am guilty of using a black box if I like what it does to my music (though when reviewing, I take the ADE-24 in and out of the system to make comparisons). I listened to the Soaring amp with and without the SLC engaged, and the effect of the circuitry was clearly audible.

I was excited about trying the Soaring Audio SLC-A300 because I am searching for an amp to drive my Magnepan 1.6QRs. These planars suck up all of the juice you can throw at them, and are quite revealing. My current Parasound 1500 amp is a decent match, but I have been looking for an amp with a little more current and a more relaxed and refined sound.

The first thing that surprised me about the SLC-A300 was the number of volume controls and LEDs on the front panel. The gain controls allow you to dial in as much Signal Loss Compensation as you want, or to remove it altogether. I found it difficult to believe that it could be entirely removed from the signal path by turning the main gain control all the way up, but that is what the Soaring folks claim. The manual provides a fairly simple procedure in which you match the amp's gain with your preamp, then dial in the amount of SLC desired. The setup recommendations matched what I heard almost exactly, though the SLC's effect on the signal was a slight distraction, as I was always wondering if I had tuned the settings properly.

One of the SLC-A300's interesting design touches is its use of thirty-two small storage caps in the power supply instead of two or four huge caps. This seems to have become a trend among amp designers. The amp also uses bi-polar transistors as opposed to MOSFETS. I used to associate bi-polar transistors with a cooler sound, but not any more. The SLC-A300 also incorporates most of the requisite audiophile features in the way of power, input, and speaker connectors, and is a fairly impressive package.

The SLC-A300 seemed fairly powerful for its 100-watt power rating. It sounded smooth and reserved driving my Maggies. The Maggie QR tweeter is fairly revealing of the high-frequency performance of the upstream electronics, and the Soaring amp never let me down in the top end. Its upper midrange was buttery smooth and grain-free. I turned off my dedicated subwoofer amp and let the Soaring amp do the heavy lifting with the Maggies, and the bottom end was clean and articulate. Even though the Maggies only go down to 40-50 Hz, you can still hear and feel what a muscle amp does for them in the bass. The SLC-A300's low bass and mid bass sounded very clean and tight.

The amp was not soft or mushy, but neither did it have razor sharp detail or punch. It was incapable of sounding harsh or bright, and there was no trace of edginess or grain at any time. The SLC circuitry seemed to smooth the sound and make everything seem rounder, darker, and more tube-like. If I had to guess, I'd say it was adding odd-order harmonics, but I doubt the explanation is that simple.

Did I mention that the amp sounded FAST? One of my favorite recordings is the Cactus Choir CD available on www.cdbaby.com. The Soaring amp revealed all of the Choir's Eagles-meets-Beach Boys harmonies with all of the detail and image layering that is in this great recording. I had never heard it sound more musical or real. Percussion sounds really floated in space. Does the SLC manipulate phase? If it does, I like the effect. It's very non-fatiguing.

Soaring Audio states that the amp "allows you to hear deeper into the rest of your audio system. You will hear things on your favorite CDs and DVDs that have remained hidden for years. It is like hearing a piece for the first time." While I didn't hear things that were buried for years, I did enjoy certain favorite recordings, and they did sound more present and in-the-room than they did with other amps that I have recently heard.

The Soaring SLC-A300 is a fine amplifier with a unique feature. At $3400, it has a lot of competition, but if you look carefully at its features, specs, design, and parts quality, it appears to be priced very fairly. I might have found a match for my Maggies. Greg Ewing

SLC-A300 amplifier
Retail: $3400

Soaring Audio
web address: www.soaringaudio.com

 

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