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Positive Feedback ISSUE 39
september/october 2008


wyred 4 sound

ST 500 amplifier

as reviewed by John Potis






Tidal Audio Pianos, Thiel CS 2.4s, Ohm Acoustics Walsh 4.5 mk.2s, Hørning Perikles Ultimates, Genesis Advanced Technologies G-928 subwoofers (2), Bryston 10B-Sub Active Electronic crossover.

Bel Canto Pre2P preamplifier. Art Audio Carissa amplifier, Bel Canto e.One REF1000 amplifiers, Canary CA 330 amplifiers, Opera Audio Cyber 211 amplifiers, and a Musical Fidelity A5 integrated.

Merrill-Scillia Research MS2 table, Hadcock GH Export arm, Ortofon Kontrapunkt H cartridge; Accustic Arts Drive 1/Audio Aero Prima SE DAC.

JPS Labs Superconductor 3 speaker cables and analog and digital interconnects, JPS Power AC, Analog AC, Digital AC, Aluminata and Kaptovator power cords.

GEM Dandy Hydraulic LP Cleaner, Sound Mechanics Performance Platform, Gingko Audio Mini-Clouds, 2-inch Butcher Block platforms with Quest for Sound Isol-pads, Vibrapod Isolators and Cones, Ultra & Heavy Zsleeves, Viablue QTC spikes, Auric Illuminator. Balanced Power Technology 3.5 Signature Plus with JPS Aluminata Power Cord.


The Wyred 4 Sound ST 500 amplifier is an extremely powerful amplifier at an exceptionally affordable price that will find great appeal among the rabid audiophiles among us as well as to audio newbies and music lovers just looking to choose an amplifier they can live with and be done with their search. This latter group won't appreciate sifting through thousands and thousands of words describing in minute detail the intricacies of the amplifier's personality; they just want a bottom-line assessment. So for the benefit of this group I'll just come to the point: in some ways the Wyred 4 Sound is a ground breaking accomplishment that'll bring a new level of power and sophistication to a budget conscious listening audience that could only dream of such performance before. There's no magic or hocus-pocus accounting for why this is and there's no reason for suspicion, either. The ST 500 is just the culmination of some great ideas and fortuitous (for the customer) circumstances that lead to its development.

Most readers probably aren't familiar with the Wyred 4 Sound name and they probably won't be any more familiar with that of Cullen Circuits, the firm behind Wyred 4 Sound. But Cullen Circuits has been around for 18 years and they've been doing development and manufacturing work for companies with widely known names such as PS Audio, Camelot, Arnie Nudell's Infinity and Genesis Technologies, James Bongiorno's Ampzilla, and BGW, a well-known supplier of professional amplifiers. Cullen Circuits was founded in 1990 and up until recently has been kept busy manufacturing product for PS Audio. Unfortunately, PS Audio has decided to go offshore for their production, which left Cullen Circuits in a bit of a lurch. The solution to their predicament was to found Wyred 4 Sound and take control over their own destiny.

The Wyred 4 Sound amplifiers are analog switching amplifiers that employ the ICEpower module developed by Bang & Olufsen and Dr. Karsten Neilsen. This is no fly-by-night technology as these IcePower modules have been utilized in amplifiers from Bel Canto, Red Dragon, Jeff Rowland Research and many others. Matters of sonics aside, what makes these amplifiers special is their efficiency. First, they make much greater use of the voltage coming from your wall as they transform your household current into the signal going to your speakers with much greater efficiency and much less heat than more conventional types of amplifiers. These amplifiers are also much more efficient to manufacture because they don't require massive transformers and power supplies found in other types of amplifiers. Pick up a conventional amplifier and a great deal of the weight is owed directly to that power supply. Eliminating it means that it doesn't have to be manufactured or purchased and that saves on manufacturing costs, big time. It also doesn't have to be shipped and getting a light-weight analog switching amplifier to your door gets a lot cheaper, too. Then there's the space savings requiring less rack space in your listening room—the amplifiers are absolutely tiny considering their power output. This all adds up to great savings to the final customer.

But Wyred 4 Sound takes being frugal to another level. Forget heavy brushed aluminum face plates and trophy construction. From what I gather, we'd all be shocked if we knew how much a fancy case adds to the price of a component and even more so if we knew the relative expenditures for the casework and the components inside. Wyred 4 Sound builds with an eye to attractive yet comparatively inexpensive construction. It's very solidly built and connective hardware is very good and much better than some other products in its price range. We're talking about chassis-mounted heavy-duty gold-plated RCA plugs and balanced XLR inputs—the ST 500 is a balanced amplifer. You won't be pulling the RCA connectors out of this amplifier with your snug-fitting interconnects. Standard is a single pair of WBT style shrouded binding posts, though my review sample came with real WBTs; a $100 option. The standard terminals look very much the same. Then there's the savings as there is no front-mounted power switch as the ST 500 is intended to be left energized at all times. And as it idles at a mere 18 watts (there's that power efficiency again) you won't likely see much if any hit on your electric bill as the amplifier stands ready to deliver at a moment's notice.

As far as casework goes, the 17"w x 4"h x 13"d and ca. 18- pound ST 500 looks nice but close investigation reveals very economical construction. It's completely encased in heavy sheet-metal without the aforementioned ½-inch brushed aluminum face plate. The metal itself is of very heavy gauge and there's nothing flimsy about it. While other companies are utilizing mono platforms that require two power cords and two separate cases, the ST 500 is a stereo amplifier with one case. (For those who need or prefer mono block amplifiers, the SX 500 MkII mono blocks are available for $1798 per pair equipped with WBT binding posts and is said to utilize the exact same circuitry.) It's also nicely finished with a textured paint that looks nice, even if it doesn't produce the luster of bushed aluminum. Quality soft-rubber footers, the same ones found on my Bel Canto gear, are used and the ST 500 utilizes a very unique LED bar as a pilot light that glows a very subdued violet/blue that is just visible in bright light but doesn't even come close to becoming obtrusively bright in the dark. There's even a potentiometer on the bottom of the amp used to further dim or turn it off completely. In short, construction is distinctly not fancy, but anything but cheap, and it'll save buyers a lot of money.

The ST-500 is sold either internet direct or thru Underwood HiFi. There's considerable debate as to how much this saves the buyer. With typical 100% mark-ups by dealers, there's certainly some savings to purchasers, but in such situations the manufacturer must take on all marketing and handling/repair responsibilities and these costs must be taken into consideration. So while it's probably not accurate to say that cutting out the dealer saves 50% of the purchase price, I'd think that there's got to be a 25% to 30% savings there.

So where are we? We've got an ICEpower based amplifier that saves bunches on parts cost. We've got solid build quality that is anything but extravagant and we've got a relatively efficient means of distribution. That's three distinct areas of cost-cutting that is easily passed right along to the buyer. As I said, there's no magic here and suspicious readers can stop waiting for the other foot to fall. There's no downside here.

And what of this ICEpower module and its analog switching amplifier technology? Well, astute audiophiles will, no doubt, be very familiar with and will have read many reviews of amplifiers based on the ICEpower module already. For a few years now I've been listening to Bel Canto's e.One Reference 1000 mono amplifiers. I gave them 6moons' very first Lunar Eclipse award ever bestowed on a piece of electronics following their review. The Wyred 4 Sound ST 500 amplifier uses extremely similar technology, though designed to deliver roughly half of the power. The ST 500 only produces 550 watts into 4 Ohms and 250 watts into 8.

But as all these amplifiers use the same ICEPower modules, they all sound alike, right? The value-minded buyer just buys the cheapest amplifier that'll suite his power needs, right? Well, no. The ICEpower module is an important piece of the technology, but it's not the entire amplifier. These analog switching amplifiers do sound different. Even amplifiers utilizing these modules within the same brand sound different. The Bel Canto S300 is a fine 150-watt (8 ohms) amplifier but it doesn't sound like the Reference 1000. This Wyred 4 Sound ST 500 doesn't sound like the 4-channel Wyred 4 Sound amplifier that I used in the Emerald Physics CS2 review. Obviously the ICEpower module is an important piece of the puzzle, but it's not the entire puzzle. Here's Rick Cullen on why that is:

There are many sonic differences with our amplifiers. The main reasons are held within our direct-coupled, balanced, dual FET input stage (input buffer). this raises the input impedance to 61.9K ohms, which allows source equipment to easily and accurately drive the amplifier.

The standard ICE modules, which are found in many other amplifiers, have 8K ohms on the positive input and 10K ohms on the negative input to the ICE amp. So if you're using RCA's, for instance, your source would be driving an 8,000 ohm load, which isn't really bad, but much harder to drive than 61.9K ohms. The lower impedance your source has to drive, the more you will experience lower volume levels and slightly higher distortion going into your amplifier. This normally changes the way a preamp can amplify the signal applied, thus giving you less than optimal sound.

Balanced amplifiers (differential, driven from + and – signals) have much better performance when driven balanced, which ours does. All the parts you will find on our input buffer are of the best quality. We use Dale Rn55D copper leaded resistors, Wima, and MUSE audio grade capacitors, and a thick traced PCB to connect everything. Audio signal doesn't sound as good through standard magnetic steel leaded resistors, and electrolytic capacitors.

Inside the FETs on all of our input buffers, there is a voltage to current conversion. This is where we get the sweeter sound. The way a FET works is the current that flows from the output (the drain to source current) is controlled by the voltage on the input (the gate). This has a softening effect that complements the slight brightness and edgy sound of the Class D amplifier. It tends to make everything softer, smoother, and more accurate. Our research has concluded that the function of our input stage has a similar sonic signature of a tube based circuit. The benefits of ours is that it is direct coupled (no coupling caps), has no feedback, and lacks the reliability issues inherent in a tube circuit.

We also perform modifications to the modules in every amplifier to enhance its performance. We bypass critical input coupling caps to allow audio to freely flow through while still allowing for DC protection, and "beef-up" the servo (feedback) circuit for enhanced bottom-end extension. Every module is connected to the binding posts with 14AWG 99.9% OFC high strand pure copper paralleled with 14AWG high strand PURE silver wire.

So… hopefully, now you understand all these analog switching amplifiers, even those using the ICEpower module don't sound the same. How does the Wyred 4 Sound ST 500 sound, you ask? Well, it sounds a lot like my Bel Canto e.One Reference 1000 mono amplifiers, as it turns out. A lot like them.

Though I was told that the 4-channel Wyred 4 Sound amplifier I used in the Emerald Physics review contained two channels of the same chip used in the Bel Canto amplifiers, one quick listen revealed that they did not sound like my Bel Cantos. They didn't sound bad, don't get me wrong. They were actually quite nice; they were just different. Actually, they reminded me of the Bel Canto S300 that I'd recently used on another project. Following that review I was talking to Wyred 4 Sound distributor, Underwood HiFi's Walter Liederman, who told me that, indeed, they did sound different because they used a different input stage. That's when he told me of the ST 500 and how it used yet another completely different input. My curiosity was piqued.

In fact, the ST 500 sounded so similar to my own Bel Cantos that it's difficult to discuss one without mentioning the other. This is because I've owned and written and talked about the Bel Cantos for so long. I couldn't begin to count how many Emails I've exchanged on the subject of the Bel Canto amps. One reader summed them up even better than I did in my original review when he said that they were the least-bright amps that still allowed all of the important details to come through. If you know the amps as well as I do, that'll hit the nail right on the head for ya.

Least bright. Some have called them sweet; others call them rolled-off. It depends on your perspective. I've never seen them called rolled-off in a review. But when other amps under review are compared to them, then suddenly the Bel Cantos are referred to as sounding rolled-off in the highs. I guess that's what you do when you're reviewing something else—you write in terms that will cast a positive light on what you're writing about right now. And in side-by-side comparisons, I suppose that they do sound that way. But they never do in long-term listening sessions. They don't sound dark, they don't sound rolled off. They don't sound lacking in sparkle, air or detail, either. That's why I use them. They sound musically natural to these ears… with most speakers.

Most speakers, particularly in the lower-priced designed-by-the-numbers ranks do sound bright to a lot of people. If not bright, we'll call them energetic and lively. Or even forward. They're designed that way to sound great in a short-term audition in a showroom. But in the long term, listeners start to hear bright. They start looking for cables and wires to tone them down a little. Not a lot… they're not that bad. They just start looking for ways to smooth them out a little. This is when the Bel Canto amps—and now the ST 500-- just sound remarkable. They're not so rolled off or colored that they'll change the character of the speakers you're using, but they'll smooth them out just a little. They'll help them to relax. You won't lose any detail, it'll all be there; it just isn't thrown up in your face.

In my years with the Bel Cantos I've only had one speaker that didn't shine with them; the Acoustic Zen Adagio Jr. This is one warm and reserved sounding speaker that proved to be too much of a good thing with the Bel Cantos. But every other speaker I've had through here in the intervening years proved to be completely copasetic—most were downright synergistic. My own Tidal Piano loudspeakers don't have a bright or forward bone in their cabinets. They're exceptionally smooth and the antithesis of forward, hard or etched, but they sounded wonderful when connected to the Bel Cantos, er, I mean the ST 500. OK, they sound great with both.

All of this adds up to what I said before; that the Wyred 4 Sound is a ground breaking accomplishment that'll bring a new level of power and sophistication to a budget conscious listening audience that could only dream about such performance before. If you're shopping around for a system in and around the same price class as the ST 500, you're going to hear a lot of speakers as I just described. The ST 500 will combine with them for a sound that is sophisticatedly smooth and articulate. We're talking real synergism here.

Of course, in terms of power, well, we're talking about a robust 550 watts into 4 ohms; we're talking about some real delivery of current that you won't find in any other sub $1,500 amplifiers that I know of. We're talking practically unlimited drive.  And there's no sonic penalty, either. By that I mean that it's well-known that there are many muscle amps that sound great into difficult loads, but which can't get out of their own muscle-bound way into higher efficiency speakers. They just can't get it out of first gear with these speakers. That's not the case here. The ST 500 doesn't lose its composure when it's allowed to loaf along.

The ST 500 has an excellent bass character. It's very highly damped and very controlled. Many a listener will hear less boom and less distortion from their speakers but more tune, tone, and articulation in the bass. Such controlled deep bass also makes for better continuity through the upper bass and lower midrange, which builds a better and cleaner bridge to the midrange.

Of course, the ST 500 has a beautiful midrange. Detailed and smooth. And like my own Bel Cantos, they set themselves apart from a lot of solid-state amplifiers in this price range by throwing an extremely reach-out-and-touch-it soundstage. With these amplifiers the instruments are as physically in-the-room as I've ever heard from a solid-state amplifier, and more so than a lot inexpensive tube ones, too. Forget light and ethereal, this amplifier boarders on becoming a visual experience. The soundstage is wide and deep, when the music calls for it, too.

Through the treble, in anything other than a direct-comparison with something else, it sounds extended, musically detailed and solid. Of course, a lot of other amplifiers will now sound hard and etched as compared to the ST 500—again, it depends on your speakers and your perspective. For a lot of listeners with a lot of speakers, the ST 500 will sound musically relaxed and sophisticatedly smooth. It'll sound more natural; more like real music. There's no artificial air or detail.

Orchestra and Big Band recordings come across big and solid with the ST 500. Carved In Stone by the dmp Big Band [DMP CD-512] was nothing short of luscious with full bass and solid imaging that was, indeed, carved in stone. Horns were big and full without glare or strain but otherwise full of energy and bite. The acoustic basses showcased the ST 500s authority down low with ample and tuneful bass runs that propelled the music along. While there was no exaggerated sense of air (do you hear air in a concert hall?) there was a great sense of space both surrounding the orchestra and between the instruments. This includes lots of soundstage depth, too.

I confess to having very pedestrian tastes in music (which is OK as there are already plenty of music snobs out there) and the Wyred 4 Sound ST 500 loves it as much as I do. Take Smash Mouth's Astro Lounge, for example. No matter how loud I wanted to go, the ST 500 was right there with me with powerful bass lines that never strained. Crank up "Road Man" with its reggae style rhythm and see if you can not bob your head and tap those feet. "Fallen Horses" should make your speakers vanish in place as the music suddenly fills in the front corners of your room. I won't tell you how many times I hit the back button on the remote here. But "Defeat You" sounded even better. The opening guitar riff came from the extreme left side of my room and I could have driven a Mack truck between instruments and there was a level of transparency here that was missing on most of the first half of the tracks on the disc. The ST 500 provided me with a connection to the music that few amplifiers do and its warm natural character allowed me to turn up the music with no sense of strain and minimal fatigue.

Dynamics? Forget about it. This amp is powerful, but it doesn't have lead feet. It's pretty darned nimble. It's one solid-state amplifier that doesn't sound like a clod, even after listening to Single Ended Triodes all these years. No, it's not a triode amp, but it needs to apologize for nothing as triodes can't match this level of power and drive. As much fun as I was having, nothing prepared me for "Home" that, again, went wall-to-wall in my room but was accompanied by a huge bass line. We're talking wall-flexing bass, here, of the most unrestrained sort. We're talking fun with a bit phat capital "F". Now I regularly run these Tidals with as little as 26-watts per channel and they do… alright, dynamically speaking. But sometimes there's just something to be said for having more power… Scotty was so right.

By the way, I'm quite certain that the bulk of readers already know this but it bears repeating for the benefit of those who may not: big amplifiers save speakers, they don't destroy them. If you're just getting by with an amplifier of barely enough power, you're presenting your speakers with a lot more risk than if you had a much more powerful amplifier. Small amplifiers—particularly solid-state ones—distort heavily when they are overdriven-- when they clip. This distortion sends unnaturally high levels of electronic grunge not found in music to tweeters and it burns out their voice coils. On the other hand, powerful amplifiers are seldom driven to distortion. Sure, you can overdrive your speakers if you're stupid and hell-bent on destroying your ears, too. But if you observe prudent listening levels and pay attention for any signs of distress from your speakers (in which case just turn down the volume a smidge) the ST 500 will pose no threat to your speakers, no matter their power rating.

I loved the effect of the ST 500's tonal balance on classical music. All the detail was there and the soundstage was cavernous. But the ST 500's sweetness ensured that high percussion, strings and brass had no glassy overlay; there was never any sense of unnatural glare and no artificial spotlighting on any section of the orchestra. Nothing harsh and no edge, either. Such was the case with Tchaikovsky's Symphony no. 6 on Pentatone's SACD [5186 107]. I also loved the way the ST 500 portrayed the size and depth of the basses, which were weighty yet rhythmic and detailed. It was extremely easy to differentiate their contributions from those reflected and reverberated within the hall, which served to help place me within that hall. The music ebbed and flowed as it should and when the music was supposed to be big, it was massive and weighty. Overall the ST 500 has a natural sense of ease about it that served the music as well just where one would expect.


Make no mistake; this is no intermediate amplifier. This is not an amplifier to buy while you're saving to buy something better at some time in the future. You'll have to save up a lot of money to get something appreciably better. In fact, if you're in the market for a big and powerful yet sophisticated sounding solid-state amplifier and you have thrice the ST 500's asking price budgeted, you should consider this amplifier. You could save a lot of money here and put it toward better speakers, front-end or your preamplifier. Incidentally, I spent some time with the Rogue Audio $995 tube Metis preamplifier in the system and the combination was silly good. Particularly if you are CD only (though the Metis includes a phono stage), the $2494 Metis/ST 500 combo will stand up to most speakers costing many times more and they'll have you questioning the logic of spending more. Seriously. I'm listening to it right now!

My only caveat is one that will be meaningful to a very small percentage of buyers and I refer to its sweet overall balance. Owners of speakers considered almost too laid back and too sweet on top already will want to avoid the ST 500 as the combination will probably prove to be too much of a good thing. The ST 500 will serve speakers of a neutral or forward personality much better.

Of course, audiophiles will be audiophiles. And if you insist on getting something built with an eye toward ornamentation, I won't blame you. We spend as much time looking at this stuff as we do listening to it; we should be comfortable looking at it. And for sure there are other flavors of amplifiers out there and that anal inner-child in us will always be curious about what else is out there. That's normal. It's part of the human condition. Go ahead and spend more money and get something that inspires that pride of ownership thing and I won't say a word. Just don't convince yourself that you're getting something that serves the music better. Not if you're shopping at anywhere near this price class, anyway. Because if it's good music that is the goal here and you're looking for a high-powered solid-state amplifier, the Wyred 4 Sound ST 500 comes too damned close to the best out there at a price way too reasonable to be ignored. John Potis

  • Powered by ICE POWER®.

  • Factory Selectable mains 115/230VAC

  • Thermal protection

  • Over current protection

  • DC output protection

  • Sound optimized soft clip

  • Standard 12V DC Trigger

  • 1/2" Milled and Anodized Aluminum trim panels

  • Gold plated insulated 5 way binding posts

  • Gold plated unbalanced (RCA) input

  • Neutrik Balanced (XLR) input

  • Exceptional input stage raises input impedance to 61.9K Ohms

  • 17"W x 4"H x 13"D


ST 500 Stereo Power Amplifier
Retail: $1499

Wyred 4 Sound
2323 Tuley Rd. Unit A
Paso Robles, CA 93446
TEL: 805.237.2113
web address:

Underwood HiFi
9960 Bankside Drive
Roswell GA, 30076
TEL: 770.667.5633
email address: [email protected]
web address: