From Positive Feedback magazine, Vol. 6, No. 4
Also online at www.positive-feedback.com
Reprinted with Permission
(Note: The 1KW circuit is the same as in the original Musician)
The Spectron 1KW DIGITAL Amplifier - A Pure Class D Killer!
By Mike Pappas, Associate Editor, Digital Technology
A Pure Class D Project
How did I get into this? Well, our fearless editor David Robinson called me about eight weeks ago and told me one of the most fantastic tales I have ever heard....
It seems he had gotten a call from one of the co-founders of Infinity, a John Ulrick, who was now the owner of a company called Spectron. He had created an amplifier and was looking to get it reviewed. So what is so fantastic about that? Well it seems that this amplifier is a solid state class D pulse width modulated (PWM) amplifier. That's right, a fully digital power amp!
Now many of you know my musical listening propensity leans towards solid state and digital, so David figured I was the perfect person to give this amp a listen.
Now I have to admit that my initial reaction to the whole idea of a digital amp was one of apprehension. I know how difficult it is to build great digital head end gear. I couldn't even imagine what it would take to build a digital power amp that would qualify for audiophile grade. I had a really bad feeling that this was going to be another one of those products that got returned back to the manufacturer as "Not Reviewable".
A couple of days later I got a call from John Ulrick. We spent a couple of hours on the phone discussing him and his amplifier. John has a great story and it's best to let him tell it in his own words.
John Ulrick Tells The Spectron Story
Please see John's Story
The Spectron Arrives!
A couple of days later UPS rings the door and the Spectron PWM amplifier arrived. I cracked open the box and unpacked it.
The Spectron 1KW's aerospace/milspec legacy is readily apparent in the looks of this amplifier. The no nonsense exterior is formed of a heavy gauge aluminum skin which has a black anodized finish. Phillips head screws are liberally slathered all over the top and sides, as all of the major subassemblies are bolted to both the top and bottom half of the exterior shell. This creates an incredibly strong and lightweight assembly that could probably survive being hit by an anti-tank weapon.
The thick front panel is nicely machined out of aluminum and powder coated with large gold plated volume controls. A cutout located in the center of the front panel has the filter for the fan. A well proportioned power switch is located in the right corner with a corresponding green LED that indicates if the amplifier is powered up. Indicators are provided to indicate if the fan is on and via LED intensity, how much air is being drawn into the amplifier. Two "bar graph" type LED displays are provided for each channel indicating the amount of voltage in ten 8 volt steps and current in ten 5 amp steps being delivered by each channel. The bar graph displays can be a bit disconcerting. I found however, that after a couple of hours I didn't even notice them unless I wanted to know how much power I was putting into the Radians. These displays along with individual channel status and fault indicators are located behind a pair of discreet smoked Plexiglas windows.
On the back of the amplifier, provisions have been made for both balanced inputs on XLR type connectors and unbalanced inputs on RCA jacks. A label on the back notes that the unbalanced inputs are polarity inverting while the balanced inputs adhere to the industry standard pin 2 hot configuration. A pair of 5 way binding posts provide the output connections to the speakers and an IEC type power connector is provided for the mains cable.
Pulling the top cover revealed neat wiring, a good sized toroidal transformer and a pair of power supply caps. A 40 watt switching supply provides power for the displays and the cooling fan. All circuit boards are glass epoxy with the extensive use of surface mount devices to increase density.
The Class D output stages are comprised of 4 MOSFETs per channel which, with their corresponding modulator circuits, are mounted on nicely machined thick aluminum blocks.
I initially couldn't get over how small and lightweight this amp was. I am used to these hulking behemoth power amps that take two guys and a small child to move. In comparison, the Spectron 1KW is tiny, It weighs in at 34 pounds (less than my VIMAK CD transport) and it's only 3.5 inches tall.
Sitting next to my Crown Macro Reference amp, which is a whopping 7 inches tall and weighs in at 65 pounds, the Spectron 1KW looked like the stereotypical skinny kid at the beach. This lack of physical magnitude can be directly attributed to its Class D heritage.
In a conventional solid state amplifier the Class A & AB output stage has about 60% efficiency. Driven at 500 watts into a 4 ohm load, each of the output stages would draw 900 watts (1,800 watts total) from the power supply. Obviously you need a pretty beefy power supply with a large transformer and big caps to keep up with this. Since each of the amp stages are dissipating 400 watts as heat, large heat sinks are needed (or in the case of the Crown, a computer controller fan is used) to keep from melting the output devices.
By comparison, the Spectron 1KW's Class D PWM amplifier stages are 90% efficient. If we drive the 1KW at full rated power of 500 watts into a 4 ohm load, the amp channel is only drawing 550 watts from the power supply. Driving both channels at 500 watts results in drawing only 1,100 from the power supply, which is 700 watts less than a comparable solid state amp. This means that the power supply transformer and caps can be much, much smaller while delivering the same amount of power to the speakers. Due to the high efficiency, only 50 watts per channel is being dissipated as heat. In the case of the 1KW, the heat sinks are very small, with a very tiny fan. If you factor in the efficiency of the power supply, the Spectron 1KW has an efficiency of about 82%. All of this efficiency results in an amplifier that is very compact and lightweight.
Listening To The Beastie
So now with the technical end of the amplifier covered we get down to the really important stuff - how it sounds.
I powered up the Spectron amp and let it run at low level for a couple of days before starting my initial listening tests. I rounded up twice the usual number of my favorite CDs and sat back for a listen.
I started with Pat Metheny's Letter From Home and dialed up the first cut. The next thing that I knew, the CD was over and I was picking up my jaw from off the floor. There's no way that this amplifier is that good!! This disk never sounded like this. The air. The space. The depth. The ease. It just immersed me. This can't be right. It must be some sort of a bizarre symbiotic thing going on with this particular disk.
I grabbed my old reliable Chet Baker and Gerry Mulligan 1974 Carnegie Hall recording and dialed up "Song for Strayhorn." This is really bizarre, I am hearing a triangle that I have never heard before. This gets even weirder as the applause is just like sitting in the hall. I can hear the first person clapping - and the next 10 people joining in - and then the whole hall - and then the applause gradually starts to trail off until I can hear the last person stop clapping. No this isn't possible! There is something uncanny going on here. Is this the Twilight Zone? How could this amplifier be letting me hear all of this?
I have got to try another disk. I grabbed Crosby, Stills, Nash and Young, Four Way Street. This is a funky live recording that has great tunes with what I have always considered to be very marginal engineering. I dialed up "Lee Shore" and sat back for a taste. There is really something off here. The vocal haze that was always on this cut is gone. I can hear the harmonies with crystal clarity that has never existed on any system I have ever heard. I dialed up "Triad" and again the total lack of haze was shocking! The sound stage which used to be constricted was huge and extended way beyond the speakers.
I figure that I am part of some sort of alien audiophile abduction. Kind of like the alien equivalent of "I heard these things that I have never heard before" and "I was transported to a new musical experience level that I never thought was possible." I was waiting for Agent Scully from the Fox series The X Files to break down the door and rescue me!
Well, by now I was in it this thing far enough; I figured that I better get a second opinion to make sure that I haven't been part of some extraterrestrial experiment. I invited an audiophile buddy of mine, John Mikity over for a couple of listening sessions.
I played many of the same cuts as above, and his response was the same as mine: incredulous! This amplifier can't be doing the things that we are hearing. The Spectron 1KW was presenting us with an incomprehensible amount of stunningly musical information that we had never heard before.
So now we have a challenge. Let's dig up some old moldy stuff and let's see what this amp can do to it. We try firingup Neil Young's Harvest CD, and we dial up "Old Man". The first thing that we noticed was that the kick drum, which always sounded like a flatulating lawn mower had been fixed. The kick drum now had click, snap, and punch. There is a piano part that floats in which, until we listened to this amplifier, we had never heard.
Since words are the tools of the audiophile writer, we will try to reiterate what we think we are hearing in the typical audiophile jargon.
Sound stage: John says you can swim through the layers and textures. I say that it is gloriously wide and deep with everything in it's proper perspective. We both agree that we haven't had an amp in this system that got even close to presenting the delicate tapestry of a sound stage like the Spectron did.
Imaging: Like a rock with pinpoint accuracy that doesn't change with amplitude. Images just locked right in and soon after you start listening, you forget that imaging was ever anything that used to be a problem. After five 3 hour listening sessions, we both concurred that we had never heard any amplifier that could convey this kind of "dead on" imaging accuracy.
Air: Oh Baby, does this amp have air. The overhead cymbals on the Pat Metheny recordings will launch you into another universe. The air that surrounds cymbals, percussion and the like are one of the true wonders of this amplifier.
Dynamics: Certified to be Space Shuttle launch capable. For example, we were playing a Dire Straits cut from their On Every Street recording. I had cranked up the level and my cat, Talos, was laying down on the floor between the speakers. We rolled into the cut and when the snare drum got whacked, Talos shot straight up in the air about three feet and vanished! This amp has got better transients and macro dynamic resolving power than anything I have ever been exposed to.
Power: By now you all know that I am a major power junky. The way I figure it is if your amp wimps out when you push it, the transients just won't get through (except as nasty clipping artifacts). Rest assured dear reader, that this amplifier has the necessary power to get just about any transient, short of thermonuclear warfare, through even the most inefficient speakers made. Since I am a charter member of the "More Power, Dammit Scotty!" hall of fame, I am hoping that Spectron will offer a bridged mono pair for those of us looking for the ultimate in headroom. (Ask and ye shall receive; check my note at the end of this review!)
Control: This amp has more authority than a room full of control freaks. Tight snap and great damping factor make this amp have some of the best woofer control that I have ever heard!
Haze: This amp has more clarity than the repaired Hubbell space telescope. It will open up your music like a crystal clear picture of a far off galaxy. Absolutely nothing gets lost in the transition from soft to loud and back to soft. This is a problem that every linear amplifier that I have ever heard could not totally resolve. Words are incapable of fully describing the sheer resolving power of this amp.
Musicality: Oh my god, this amp has all of the above and to top it off, it's musical! For a full dissertation on the amplifier's musicality, see the next section below.
Turn it on and Crank it up factor: You have all heard (or maybe owned) gear that did everything "right" - and you just didn't want to spend any time listening to it. Well the Spectron 1KW isn't one of them. This is a 100% guaranteed toe tapping, drink a whole bottle of single malt until the sun comes up, want to play more until the wife tosses everybody out kind of a product. Suffice it to say that metaphorically speaking, this amplifier goes to 11 on a scale of 1-10...
An example of what I mean is in order at this point. First you need to get in to Mr. Peabody's "Way Back" machine and set the time indicator to 1972. When the door opens, get out and remember when you first heard Emerson, Lake and Palmer's Trilogy. Nice tunes but not a world class recording. Wrong! With the exception of the piano on the Sheriff cut (which gets a bit crunchy on the crescendo), this recording has got great sound. The drum introduction on the "Sheriff" cut has impressive snap, killer transients, and the vocals will knock you and your preconceived notions right on your butt.
On recordings made during the pre-digital time millennium, the analog tape hiss is certainly present, but with this amplifier it is not objectionable like it was with other amplifiers. You can hear it, but it doesn't have the edge that used to drive me right up a wall.
OK, so maybe both John and myself were abducted by audiophile aliens, but I don't think so. I think we were both shanghaied by one of the finest audio amplifiers that we have ever heard, and through it, transported to a new universe of listening pleasure.
"So how do you really feel about this amplifier?"
The Spectron 1KW amplifier redefines the state of the art in power amplifier designs. It does everything right, so right that words cannot totally convey what this amplifier is capable of doing. (Yeah, I'm considering setting fire to the old word processor!) And that isn't the half of it. I've saved the best for last. If this amp cost an arm and a leg, or you had to auction your significant other to even daydream about it, that would be one thing. You could read this review, shrug your shoulders, and say, "Hell! Another damned amp I can't possibly afford!"
BUT - and hang on to yer shorts, Mort - at an MSRP of just $3,495, the Spectron 1KW is a bona fide killer!! Competitors are hereby served notice that the Spectron 1KW is a bone-bustin' foe requiring a wide berth....
Even more: wait until I tell you about what a mono pair of these suckers did to my sweet spot!