150 WPC Power Amplifier with "Audio Signal Loss Compensator"
PRICE:$2,100
Soaring Audio is an out of the way hi-fi company with an off the beaten path product. The SLC A300 amplifier is a basic amp combined with a proprietary signal processor. Its raison d’etre is to showcase the patented Soaring Audio Signal Loss Compensator circuit. Per the manufacturer, the SLC A300 removes digital grunge, improves center fill, imaging and dynamics.
The amp is rated at 150 wpc into 4ohms (about where my MLs pull the most juice), so it probably runs less than 100wpc into a standard 8 ohm load. Physically, the amp is short, wide and deep, a very solid 38lbs, with sharp heat fins on both sides. BE CAREFUL. I broke a fingernail picking this amp off the floor and suffered multiple scratches from the heat sinks. Speaker connectors are high quality Cardas dual binding posts that accommodate spades only. There is an IEC connector for power, but the ground leg is missing. No worries about ground potentials with this amp. Taking the top off, the most notable features are 40 small capacitors- Soaring Audio says 36 are for the power supply, along with a large toroidal transformer. Inside and out, construction quality is very high.
There are three knobs on the front panel. The function of the Volume knob is clear. The other two, labeled R&L, set input level for the SLC circuit. Too little gain on these and no sound comes out. There are four indicator lights for each channel, two green and two red. SA instructions: The knobs should be adjusted so that the green lights flash and the loudest input level does not trigger the red lights. When the red lights did come on, I heard some nasty artifacts, and thought at one point I had fried a woofer. No real harm, but make sure the red lights stay off. In my system, this ended up being right at the SA suggested starting point, 12.00 on both channels, with the master volume set to maximum if you’re running from a preamp. The SLC A300 can also be used as a single source integrated amplifier with a CD player (more on this configuration later). It is important to note that the SLC circuit is not defeatable and its’ effects can’t be minimized.
It’s easy to snipe at the wording on the SA website. The authors are obviously not addicted to reading Stereophile and TAS. Their passion about the SLC circuit gets translated into language that makes yr humble servant and traditionally biased audiophile cringe. Could this prejudice my review? Possibly. Doesn’t affect the sound though, and I did my best to ignore their purple prose while I listened.
From the Soaring Audio Website:
I changed power cords on the amp during the course of my review, starting with the supplied 2 prong computer grade cord, and also trying cords from Zu Cable and Black Sand. I did not hear any differences with the different cords, but your mileage may vary.
Sound of Soaring Audio
First serious listening started with my favorite Tori Amos tracks from The Beekeeper. “General Joy” is as close as Tori gets to a straight ahead rock tune. My notes say bass was very heavy. Lack of air. Great vocals. Leading edge of bass transients was softened (this is kind of an oxymoron- most or all of the bass transient info is higher in frequency). These characteristics remained constant through all of my listening. Cranking the volume to mid 90db levels, sound was a little harsh though I didn’t hear any obvious compression or other nasties indicating that the amp was clipping.
As I went through other music and played with the knob settings, I wasn’t able to change the basic sound of the amp. My notes: “Its kind of like old tube sound, with the leading edges dulled instead of sharpened, not what SA claims for their circuit. On the other hand, soundstage is improved, with solid wall to wall sound.”
Some classical: Rossini on RCA Living Stereo SACD with Arthur Fiedler. Here the decrease in very high frequencies was not obvious, and the amp’s strength in the midrange resulted in a sweet string sound. Bass foundation was solid. High frequencies more like what you hear live, mid or back of the hall. That is, less than what is recorded on most CDs.
Van Cliburn’s piano, also on RCA SACD, was less detailed than what I am used to hearing on the recording, but was very natural sounding- the overall impression from the amp was consistent, short on high frequency detail, but natural for most acoustic instruments and not fatiguing.
Various LPs did not show the same loss in bass definition, as they largely don’t have that information in the first place (I am ignoring audiophile LPs and reissues here, as I have few of the former and none of the latter). LPs did not show the same black background I was able to achieve with another high power solid state amp (a Butler TDB2250), which was so quiet and had so much gain that even Melanie’s “Leftover Wine” at Carnegie Hall was transformed into a hi-fi wonderland.
SOARING WITH THREE OTHER AMPS
Since I had four amplifiers in house - the Soaring Audio SLC A300, McAlister PP150, Bryston 4B and the borrowed Butler TDB2250, I decided to run my own personal soundoff.
For direct comparisons, I decided to sacrifice two tracks that that I know well and may never listen to again for pleasure. I chose Chains and Rhiannon from Fleetwood Mac’s “The Dance.” Both of these tracks are perennial stereo show standbys, have big dynamics, plenty of kick, a variety of voices along with delicate high percussion. These two tracks were repeated several times, played through each amplifier, as fast as I could move interconnects and speaker wires.
“Dreams unwind, love’s a state of mind”
Soaring Audio SLC A300
On “Chains”: Kick drum is Huge. Soundstage is wider than my tubes. Highs are there, but rolled off. Increasing the SLC gain knobs and backing off the volume a bit raised the highs a bit. Hard to tell, and there is the danger of input overload. Plenty of power, but obviously lacking precision on bass transients compared to the other amps.
Rhiannon: Bells in the intro are there but don’t ring properly. Stevie sounds good- solid state amps can make her sound younger on this track- but not the SA. The soundstage, as promised, is solid from wall to wall. Again, solid bass but not well defined. Coupled with the wider image, I wonder if the SA amp is screwing around with phase relationships, even though they claim phase fidelity.
Butler TDB2250
The Butler is an unusual hybrid amp with octal tubes up front and bipolar transistors in the output section, rated at 250wpc into 8ohms. The unit I have is not the latest version, so Butler requested that I limit my comments. The amp exhibited high gain in my system, coupled with an almost unearthly quiet background.
“The Dance” is recorded on the thin side but as noted, there are lots of high percussion sounds and plenty of big dynamics. Through the Butler, “Chains” hits hard. Bass is detailed and controlled. On “Rhiannon”, the bells and chimes ring with real metal, exhibit natural decay and have plenty of air around them.
My notes say “Exploring the limits of the speakers. The amp’s got plenty left.” Low bass is well defined and I don’t miss the sub. Unbelievably quiet between the notes. Stevie sounds age appropriate - like the Soaring Audio, you can hear the experience in her voice, and you can easily envision Stevie herself. With this amp, I keep turning it up till my ears say no mas and I worry about the speakers - the amp doesn’t harden and the ML's go loud (peaks measured at 103db on a Radioshack meter).
Bryston 4B
This was in no way a fair test for Bryston, the company or the amp. I don’t know how old my amp is, or even if it is entirely stock. I make no claim to this as representative of the current Bryston 4BST, only know that if my amp breaks, Bryston will probably still fix it under their 20 year warranty. Anyway, this is 250wpc of solid state muscle. A traditional transistor amp, Brystons are famous for bass, which my olde 4B delivers in spades. Kick drums are faster, bass notes are cleaner than the Butler.
In “Chains”, the Bryston produced the hardest kick and the best bass definition, but lacks the warmth that the Butler provides. I can play it as loud as I dare. Percussion is mighty, but the cymbals are more fizz and less metal. Stevie sounds younger, as expected- only the head voice is apparent and I don’t see a whole singer in front of me if I close my eyes. The sound is a little more localized to the speakers. These effects are more evident with “Rhiannon”. The high tinkly percussion sounds in the intro sound synthetic and unattractive.
Very quiet, sterile and grainy in the treble. This Bryston is truly a bass master, and that is why I keep it on the bass only.
McAlister PP150
I raved about this all tube 75wpc push pull amp in an earlier review, saying it was near perfect. However, if I crank it too high, compression sets in. It plays pretty loud by itself, but 75 watts, even tube watts, don’t equal the 500 or more that the Butler and Bryston can deliver to each channel at 4 ohms. The kick-drum on “Chains” has more bottom on it than with the other amps, probably because of reduced damping factor. The bass solo also sounds deeper. Maybe not as accurate, certainly not as fast sounding as the transistor amps, but I like it. Highs are not as prominent as with the Butler or Bryston, but tones are more rounded and lifelike. Lindsey Buckingham’s voice is served best here. Stevie also. On “Rhiannon” the high percussion has a filigreed rightness that could not be replicated by the other amps, though the Butler was not far off.
Back at Soaring Audio
Towards the end of the test period, I tried running the SLC A300 as an integrated amp. You can hook up one source, but in this configuration, you optimally set the R & L input levels once, and don’t worry about losses when the preamp volume is turned down.
My classic Theta DSPro Gen II DAC, with 4V rated output, lit up the SLC red lights even when the R & L pots were turned all the way down. No good. So I connected my humble Sony player, which sounds ridiculously good given its low price. This gave me the simplest system I have ever had in my den. Down from 10 power cords to 4 (player, amp and speakers- electrostats are always plugged in). One set each of interconnects and speaker cable. Just two active boxes between me and the music. The result was very similar to the Sony run through the preamp, maybe a slight loss of dynamics (I hear the same effect comparing the Sony to the Theta, so I’m not willing to put this on the amp). No other differences worth mentioning. If you only play CDs and have a player with 2V output, this may be the way to go.
Conclusions about the SLC circuit
I would defeat it if I could.
Matching to the published SA claims-
Wider, more solid soundstage with better center fill: Met.
Improved dynamics: Met sometimes, most evident on bass notes in classical pieces.
Improved bass definition: Not met.
Removes digital grunge: Met perhaps if you think you are suffering from this malady, but… Also filters out a good bit of the music that adds excitement and delicacy to the sound
For classical music lovers, especially those who think CDs are unnaturally close-miked. Combine with a good, medium output CD player and add speakers to taste - this amp could really do the trick with speakers that have a rising top end.