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Wyred 4 Sound STI-500 Integrated Amplifier
More Pop for the Peso!


 February 2010



Wyred 4 Sound began life after its owner EJ Sarmento rose up through the ranks at Cullen Circuits and decided to begin a new company where he could take the lead and become the creative driving force. EJ worked side-by-side with Rick Cullen of Cullen Circuits who is well known and respected in the Audio Industry, having worked for companies such as Genesis Technologies, PS Audio, Infinity Systems, CAT, and others. Cullen Circuits currently supplies OEM parts and circuits to manufacturers, and electronic modules or parts for modifications of existing products. Rick Cullen is in fact co-owner of Wyred 4 Sound and it seems that he and EJ Sarmento have formed a symbiotic alliance. EJ’s role at Wyred 4 Sound is crucial as he develops the chassis, circuitry, software, and even the website design.

I originally contacted EJ Sarmento and obtained the W4S ST-500 basic power amplifier. I was very impressed with the sound of the ST-500 but did not have it long enough for a thorough evaluation. Shortly after receiving the ST-500 I saw that Wyred 4 Sound had introduced a remote controlled integrated version, the STI-500, so I exchanged the basic ST-500 amplifier for the integrated model, thinking that another $500 would be well worth the remote control and the other convenient features included on the integrated model. It is!

Description and Overview
First of all, the W4S STI-500 is actually a less powerful version of the W4S STI-1000 integrated amplifier. Its features and built-in line stage preamplifier are identical. The STI-500 uses the less powerful B&O 500ASP module instead of the B&O 1000ASP model. So for those of you who can get by with a meager 250 watts per channel at 8 ohms and 550 watts/channel at 4 ohms, you can save $500 by purchasing the STI-500. If you have efficient speakers, you simply won’t need any more power than the STI-500 will provide.

The line stage preamp employs Wyred 4 Sound’s proprietary fully balanced dual FET unity gain buffers for the inputs, and a true resistive-ladder volume control. This arrangement provides for balanced output on all inputs including the unbalanced RCA’s via internal conversion. One pair of XLR balanced inputs and 4 RCA inputs are provided. Input 5 can be used as an HT throughput if selected. All inputs are nameable. There is one pair of RCA preamp outputs, which means that the STI-500 can also be utilized as a high-quality stand alone line stage or a basic power amplifier via the HT throughput. The preamp outputs can alternately be used as a subwoofer output.

It is also worth mentioning that the input impedance of the STI-500 is higher than usual for a solid-state amplifier (over 60k-ohms), which means it can be driven more easily and in a more linear fashion with a wider range of source components.

The remote control provides for volume and balance control, input selection, display dimming options, and on-the-fly muting and phase (polarity) inversion. I would almost buy this unit just for the polarity invert feature alone being that my speakers and ears are sensitive to the effects of polarity inversion and about 50 percent of all recordings are recorded in reversed polarity. Why not avail yourself of the luxury of switching polarity at your listening seat by the touch of a button instead of shutting down your amplifier in order to swap the respective positive and negative speaker leads for each recording? Who would do that? No one I know; so why don’t most high-end manufacturers include this feature as standard on all preamps, integrateds, and DAC’s? The answer is simple… they underestimate and undervalue your hearing acuity!

Getting back to describing the STI-500, the front panel is fairly Spartan, containing push buttons for input selection and muting and a rotary volume control that pushes in for turning on the VFD display/preamp activation, and the input naming function.

The input naming is fairly straight-forward and only took me a couple of tries to get it right. The VDF display has a 3-position dimmer, plus a fully-off setting. It is readable from 8 to 10 feet if your eyesight is reasonably good.


The rear panel contains the array of high-quality input and output connectors and a female IEC AC receptacle. The XLR input is by Neutrik, the RCA’s are gold-plated copper, and the multi-way speaker posts are made of highly ductile copper alloy that will easily accept most common connector types. The STI-500 is also equipped with a 12-volt trigger input and output, which I did not use or test, but its function was explained to me by EJ Sarmento thusly: “The trigger-in activates the HT bypass feature, if this feature is not set-up in the display the unit won't do anything when triggered. The trigger output works like any other. When the unit is on, the trigger is on, and visa-versa.”

Aesthetically, the STI-500’s multi-vented enclosure with machined corner accents is somewhat industrial in appearance… or kind of attractive in an understated way, if you prefer. But if you’re like me, the appeal of this amplifier will lie in its inner, not outer, beauty. The STI-500 is available in either black or silver finish for the chassis, with the aforementioned corner accents in black.

Installation and tweaking
The STI-500 installs in a system as easily as any other amplifier. It has a well-worded owner’s manual and its control functions are easily understood by anyone who can set an alarm clock.

As a bonus for reading this review, I will share with you the information I received about the volume control’s stepped operation. The way it works is as follows:

Volume 1 = -89dB
Volume 1-5 is in 6dB steps
Volume 5-50 is in 2dB steps
Volume 50-60 is in 1dB steps

Additionally, if you move higher than “30” in volume, the volume resets to “23” the next time the display is powered on. This worked well for me because with my sources and recordings my volume settings typically ranged from the low 30’s to the high 40’s. And you can use the Mute function to silence the sound at any time.

The first time I played the amplifier (with no break-in) it had a slight forwardness/coloration in the lower treble, but this quickly diminished after several hours of play. The sound of the amplifier continues to improve with use and sounds smoother and more musical as I go. Wyred 4 Sound suggests that its full potential is reached at about 300 hours of playing time.

I used the STI-500 in my system in two ways. In one instance I ran my solid-state phono stage directly into the STI-500 via the RCA inputs, which yielded an extremely gratifying, musical, focused, and detailed performance. The other way I used the amp was with a very good 6SN7 tube line buffer/preamp between the source and the amp input. Mind you, these two configurations did not use the HT throughput feature to bypass the preamp’s features. Since I already had experience with W4S’s basic power amp, the ST-500, in conjunction with the same tube line stage, I was able to determine that going through the integrated’s preamp section did not change the presentation in any appreciable way. As a matter of fact, if anything, my impression is that the W4S integrated version of the amplifier sounds slightly better than the basic power amp (not the other way around as one might reasonably expect). This of course speaks volumes about the neutrality and apt integration of the preamp section to the power amp section.

When I intimated my impression to Wyred’s EJ Sarmento he said that he didn’t have an explanation for my finding but that another owner of the STI-500 who had auditioned the ST-500 first had the same impression.

I experimented with a lot of different cables during this evaluation, which included different interconnects, speaker cables, and AC cords. One thing I learned is that this amplifier is very cable sensitive. Change one cable and the sound of the system changes—in timbre, in frequency balance, and in dimensionality. The perceived changes can include any combination of these parameters. But let me be clear, I have a highly tuned system and I know my recordings very well. It is not unusual for a given amplifier (be it tube, solid-state, or class D) to exhibit these types of changes when used with different cables, in fact it’s the norm at my home.

In my view, audiophiles should view this as appealing because by using different cables one can fine-tune the sound of the amplifier in situ to his/her personal ideal. Additionally, if you want a different sound down the road, you don’t need to change the amp—only a cable here or there. To me, it’s the solid-state equivalent to tube rolling.

In my system with my particular speakers, room, and associated gear, the best overall presentation I could achieve (meaning best imaging, best macro/micro dynamics, and most realistic and natural sounding) was provided by using a combination of the MAC (My Audio Cables) cables that I reviewed a short time ago. I have the MAC Palladium interconnects on my phono source, MAC UltraSilver+ Sound Pipes on my CD source, MAC CuQ Sound Pipes speaker cables, and a MAC HC Sound Pipes AC cord installed, and the sound is fantastic. This is also great news, as the MAC cables are less expensive than most competing products, and in fact are less expensive than some of the ones they replaced.

Curiously (if you read my MAC cable review), the MAC Palladium interconnects seemed to perform considerably better with the STI-500 than they did in conjunction with my Cary Audio CAD120S tube amplifier. In a nutshell, the MAC Palladiums sound more solid in the bass and noticeably better focused with the W4S amp. I used the stock ubiquitous black AC cord for a while with very good results, but it was simply outgunned by the MAC HC cord, which (not unexpectedly) proved a more synergistic match for the MAC CuQ speaker cables.

Aural Ecstasy
The reader should know that I have used many excellent amplifiers of different types in my reference system, and thus I have a very good basis for comparison to the STI-500. Among these amplifiers are the PS Audio GCA-500, NuForce Ref 9V2 SE, Cary CAD 120S, and the new Monarchy Audio SE-100 MkII Class A monoblock amps. In addition, my audiophile friend Greg let me borrow his Spectron Musician II MKII (updated with Mk3 boards) during the evaluation period.

My initial thoughts on the STI-500 are that fast transients and dynamics are rendered with startling realism as on Rodrigo y Gabriela’s 11:11 (ATO Records ATO0080). The guitar thwacking, hollow-body pounding duo’s dynamic and abrupt changes are fully exploited through this amplifier, as are their softer more melodious passages. Their rapid fingering and picking of the strings is very well delineated and the macro and micro dynamics of this recording are sensational.

Vocals, and instrumental images are particularly well defined and visceral sounding. As noted above, the timbre of the STI-500 seemed to vary with its associated cabling. With some combinations the guitars and stringed instruments would sound fantastic but brasses wouldn’t be quite right. When I switched in a different power cord then the brasses would sound excellent but strings went wanting. However, when I switched to the MAC cables for interconnects, AC power cord and speaker wire the STI-500’s timbre improved for the better and strings, brasses, and vocals were rendered lifelike and natural.

At one point, I made a power cord change that resulted in excellent resolution and timbre but a flat 2-dimensional soundstage… but it was nice because I could hear all the obscure words to songs that had formerly eluded me. Next, I swapped the MAC HC power cord onto the STI-500 and the soundstage grew back to its former enormous 3-D proportions while retaining proper timbre so I left it at that with one exception: I decided to try the MAC Palladium interconnects on my Nova Phonomena phono stage.

This turned out to be fortuitous because the Palladiums are very dimensional and musically sweet sounding cables that seemed to work very synergistically with my Michell turntable system.

I must admit I was not quite prepared for the wonderful sense of scale and all the dynamic shadings the phono was then capable of reproducing. It excelled in its portrayal of classical music. I recall playing Stravinsky’s “The Little Concerto,” and “Triumphal March of the Devil,” from Igor Stravinsky Conducts, 1961 (Columbia MS 6272). In “The Little Concerto,” the clarinet, violin, and cornet wove an interesting melody. Each instrument seemed to spring out lifelike and vibrant from a different location on the large soundstage. Changes in intensity were masterfully portrayed by the STI-500. Instruments would often play loud on first appearance and then soften and intensify as they played on. The character of each instrument was vividly portrayed and when the kettle drums began pounding in “The Triumphal March of the Devil,” they really began POUNDING. One could hear the tuning of the skins and the depth of the tones easily as they thumped away at the rear of the stage. Through the STI-500 the tympani sounded palpable and real, not merely like some blurred facsimile.

Without question this setup is the best this particular turntable system has sounded in my reference system to date.

I would be remiss in my responsibilities as a reviewer if I did not mention the spectacular vocal performance that the STI-500 elicits. Artists like Karla Bonoff, James Taylor, and Johnny Cash on vinyl and the likes of Ray Charles, Andrea Bocelli, Elvis Presley, Natalie Cole, Mary J. Blige and Reba McEntire on CD gave spirited and compelling vocal performances that could only be equaled by a very good tube amplifier or a live performance. And I know, because I’ve used a good 300B SET amp, have recently heard an excellent 2A3 SET amp on Tonian speakers at a friend’s home, and I’m presently using the VTL ST-85 amp in its triode mode in my Magnepan system (also very tough to beat on vocal music).

What I’m telling you is that with my very good 6SN7 tube line stage feeding the STI-500 through its normal RCA inputs, and with the MAC cables in place, the sound of this reference system is, in a word, “superior”. For realistic vocal performance it is among the top few systems I’ve ever heard and it fares just as well for overall performance. Therefore, the STI-500 is the most reasonably priced amplifier I know of for the level of performance it achieves.

My feeling after using the STI-500 with different components and cables is that it paints a clear, very detailed picture of what the rest of your system offers. In other words it will show your system off to its best advantage but will not editorialize beyond that which is available. Some of you may find that using the STI-500 in conjunction with all solid-state gear yields terrific results. Others, who are pre-biased toward tube sound could easily use a tube line stage or tube line buffer to give the system a more tube-like sound—albeit, tube flavor with a lot of horsepower behind it.

Finding fault with the STI-500 is not easy to do simply because it excels in so many areas. There are only two that come to mind.

First of all, it does not sound like a tube amplifier meaning that its presentation is not quite as smooth and relaxed as that of the best tube units I’ve heard. To my ears the STI-500 sounds more like an excellent battery-powered solid-state amplifier with possibly a touch more musical sweetness and a lot more dynamic pop & slam. If it has any character at all, I’d say it’s just a hint of brightness in the upper midrange or lower treble region, and the emphasis is slight if in fact it is there at all.

To put this in better perspective, in my reference system, the STI-500 sounds a bit brighter than either my Cary CAD 120S tube amp or my friend’s Spectron Musician II MkII class-D amp, and a little less bright than the Monarchy Audio SE-100 MK2 class-A solid-state mono amplifiers. And I should point out that the STI-500 is the most articulate and resolving amplifier of this group.

My second caveat concerns the lack of gratuitous glamorization to the look of the amplifier. As I mentioned, it’s sort of an unobtrusive, austere looking piece of gear.

Summing up
The Wyred 4 Sound STI-500 is an extremely impressive integrated amplifier by any measure. In a well-tuned system it can provide a noise-free, detailed, dynamic, yet immediate musical performance that can only be equaled by amplifiers costing multiples of its price. That said, there are many highly regarded amplifiers at multiples of the STI-500’s price that are simply incapable of reaching to its lofty performance level.

When one considers the high level of musical nuance and performance the STI-500 provides and then adds in the remote control and the other great features including (but not limited to) volume, balance, mute, input naming/switching, and (hallelujah!) a Phase Invert function, the benefits of ownership mount up quickly.

If your speakers could use a hefty amount of high quality power, and even if they are relatively efficient, you’d do well to put this very unpretentious amplifier on your short list. It might not be everyone’s cup of tea, as no one product is a panacea for every system and personal taste. And some might require an amplifier with more cosmetic appeal and higher price tag that doesn’t actually perform or sound better. The USA is still a free country in some respects, the last time I checked.

As for me, I know a great deal when I hear one. I’m buying this STI-500 and it will be staying put in my reference system for the foreseeable future. It’s been my pleasure to see and evaluate this well-built USA-made product that not only competes with but actually outperforms both imported and domestic products in and above its price range. Happy Listening!

Manufacturer: Wyred 4 Sound

Wyred 4 Sound STI-500 Integrated Amplifier
Power Output 8Ω @ 0.2% THD+N: 250 watts
Power Output 4Ω @ 0.2% THD+N: 550 watts
Price: $1999.00
Warranty: 3 years to the original purchaser
Visit website for complete specifications and warranty information (see below)

Unit Features (from Wyred 4
• Vacuum Fluorescent Display (VFD)
• Optical rotary encoder (volume knob/power button)
• Fully functional remote control
• 12V DC Trigger input (to automatically activate HT Bypass mode)
• 12V DC Trigger output
• Home Theater bypass (customizable for any input, also DC Trigger Input selected)
• Balance control
• Absolute phase control (0/180)
• Efficient (little heat)
• Extremely low noise floor; resistive-ladder volume control
• Unbalanced to Balanced conversion (when RCA inputs are selected)
• Extremely low Idle power consumption
• Rugged construction
• ” Machined and Anodized front panels
• 60kΩ input impedance
• 4 sets of gold plated unbalanced (RCA) inputs
• 1 set of gold plated unbalanced (RCA) outputs
• 1 set of Neutrik Balanced (XLR) inputs
• Factory Selectable mains 115/230VAC
• Compact size (17”W x 4”H x 14.5”D)

Wyred 4 Sound
2323 Tuley Rd Unit A-C
Paso Robles,Ca 93446
Phone: (805) 237-2113


























































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