Wyred4Sound DAC-2 AND STI-500 Integrated Stereo Amplifier



Recently the external DAC has made a bit of a comeback in popularity. While they were once most commonly paired with a digital transport, now you're more likely to see them hooked up as part of a home media server. With disk space now cheap enough that anyone can keep their entire collection archived in a lossless format, and even keep a backup copy of it around, people are using their PC to serve up their audio collection. However, getting the most out of that lossless archive has been a challenge for many as most computer sound cards left much to be desired in the audio quality realm. In this review, we cover the Wyred4Sound DAC-2 and STI-500 Integrated Stereo Amplifier.


  • Wyred4Sound DAC-2
  • Inputs: Two Optical, Two Coaxial, USB, I2S HDMI, AES/EBU, Home Theater Bypass
  • Outputs: RCA, XLR
  • Sample Rates: Up to 24 bit/192 kHz
  • DAC: ESS Sabre32 ES9018
  • Dimensions: 4.1" H x 8.5" W x 13.5" D
  • Weight: 16 Pounds
  • MSRP: $1,499 USA
  • Wyred4Sound STI-500 Integrated Stereo Amplifier
  • Inputs: 4 pair RCA, 1 pair XLR, 12V Trigger
  • Outputs: 1 pair RCA, 12V Trigger
  • Power: 250 WPC at 8 ohm, 550 WPC at 4 ohm
  • Dimensions: 4" H x 17" W x 14.5" D
  • Weight: 19 Pounds
  • Price: $1,999 USA
  • Wyred4Sound

DAC manufacturers saw this and began to add USB inputs to their devices to allow for an easy way to get the audio from your computer to your stereo. While initial devices only supported CD-quality sample rates, newer models are supporting 24-bit, 96 kHz sample rates, and now even 24-bit, 192 kHz sample rates as well. One of the most talked about DAC chips to recently hit the market is the ESS Sabre32 line, most well known for being the DAC in the Oppo BDP-83SE universal player. This time, Wyred4Sound has taken a different model of Sabre32 chip, the top-of-the-line ES9018, and created a new line of DACs with the chip.

The first of their two initial models is the DAC-1, which features the ESS Sabre32 chip, two coaxial and two optical inputs, and a USB input supporting 16/48 audio bitrates with both balanced and unbalanced outputs. The DAC-2 model, which I reviewed, adds support for 24/192 bitrates over USB, AES/EBU and HDMI I2S inputs, a Home Theater bypass mode with RCA inputs, a 12V trigger in and out, and a volume control.

Wyred 4 Sound is most known for their Class D amplifiers, so I also had them provide me with their STI-500 integrated amplifier to get the most out of their DAC. Built around a pair of B&O ICEpower modules, the STI-500 provides 250 watts per channel at 8 ohm, or 550 watts at 4 ohm, giving you plenty of power for any speakers you might be looking to drive.


The first thing that I noticed about the DAC-2 is that it's very large in size compared to most DAC's. The reason for this is that it uses many of the same case components as the monoblock amplifiers from Wyred4Sound, allowing them to stock fewer different parts for assembly and shipping, and lowering the costs associated with manufacturing the component. I wouldn't have minded the DAC-2 being a little smaller while in use as a desktop amp, but I'd rather have the savings passed on to me than to have a smaller, custom case.

One key feature to note with the DAC-2 is that is uses an asynchronous USB connection instead of the far more common synchronous method. In a typical synchronous connection, the DAC and computer will share a clock signal for the transfer of data over USB, which causes multiple issues. First, the speed of the USB bus isn't a multiple of the common data rates for audio, so you can't send uniform data packets at a constant interval. Second, the clocks in computers are typically very bad and subject to drift. This isn't as easy to notice on a day-to-day basis now, as most computers check the official time over the Internet and reset their clocks daily, but if you are relying on that clock for the precise transmission of thousands of packets a second, then those timing errors can show up quickly.

By using asynchronous USB the DAC-2 can get around these issues. Instead of sharing a clock, the DAC-2 uses its internal clock to keep the flow of data precise. If it starts to run low in its internal buffer, it sends a message to the computer to speed up the flow of data by a certain amount, and if it starts to receive too much data than it lets the computer know how much to slow down. This lets the DAC-2 receive the audio data at the correct rate, and reassemble them and use it's far more accurate internal clock to keep jitter much lower than on a synchronous USB connection. People might argue over how much jitter can affect the audio signal and how easily you can hear it's effects, but I think everyone will agree that keeping the level of jitter as low as possible is a good idea.

The connection on the DAC-2 that probably causes the most confusion is the HDMI port that is labeled as I2S. Whereas standard digital connections such as SPDIF carry the data with the clock signal inserted, I2S keeps the data and word clocks on separate signal paths, helping to greatly reduce jitter once again. The first appearance of using HDMI for an I2S signal was with the PS Audio Perfect Wave components. Wyred4Sound is using the same specifications in their DAC-2 so that you could hook up the PS Audio Perfect Wave Transport by HDMI and you would have an I2S digital connection between the two devices. Wyred4Sound is also working to add I2S outputs to existing players, starting with the Oppo BDP-83 so people that want to use their player as a high quality transport can do so.

Everything about the build of the DAC-2 really says quality. It arrived in perfect condition, double boxed, with good foam padding that will certainly survive multiple trips without an issue. The case itself is very solid, with nearly 20 screws keeping it in place. The connectors are all high quality, from the Neutrik XLR's to the gold plated RCA jacks that are firmly attached to the back plate with no wiggle at all. The front is kept very clean, with a VFD display, three small buttons for control and an IR sensor for the remote. Available in either silver or black, the DAC-2 might have a more utilitarian look than some other pieces of gear out there, but it's built with an industrial toughness and is as solid as anything I've seen recently.

The STI-500 came packed just as securely as the DAC-2, and built with the same high-quality components. The case is incredibly solid, with a 1/2" machined front panel, a Neutrik XLR input, the high quality, gold plated RCA jacks, high quality binding posts, the same VFD as the DAC-2, and a large volume control that also functions as a power toggle. Compared to a receiver that is in the same price range, the STI-500 was far more solidly built, with a bit of an industrial feel to it, but in the way that everything is designed around peak performance

Features that are present on the STI-500 include a 12V input and 12V output trigger, an optional pre-out and line in (for using an external crossover or room correction system, such as DEQX, with the STI), and a home theater bypass mode. This enables you to use the STI in a home theater setup quite easily, as long as your receiver or processor has a 12V trigger. When you setup the STI you can designate an input as the HT Bypass input, and run the Left and Right line outputs from your receiver to the STI, then connect the STI to your front speakers. When you turn on the receiver for a multichannel soundtrack, the 12V trigger will turn on the STI, set it to HT bypass mode, and disable all gain on the STI so that it strictly functions as a Class D amp for the front speakers.

When you wish to use an analog stereo source, you can run those components directly through the STI, letting you keep your receiver, processor, multichannel amp, and all other associated gear off. This lets you use the same pair of speakers in both a multichannel and two channel system in the same room, but still enjoying a much higher quality two channel experience than you might have using just a processor or receiver. Modern receivers and processors can do a very nice job with two channel audio as well, but as they are primarily geared towards a multichannel environment, using a separate, dedicated two channel integrated can give you both better two channel performance, and a high quality pair of amplifiers for your front speakers, without being overly complex. I fully tested this feature with the STI, and it made it much easier to integrate it into my existing system.


The DAC-2 contains a surprising number of options for a DAC. Previous units that I've seen or used had very little you could adjust, but with the DAC-2 I needed to have the manual handy for the initial setup. Volume for each input can be set to fixed or variable, depending on how you want to have the DAC-2 configured in your system. Additionally you can configured the I2S type (I didn't have an I2S component, so I skipped over this), PCM roll off, enable or disable the remote control and 12V triggers, enable the home theater bypass mode, and dim the display.

The variable volume control allows you to run the DAC-2 straight to an amplifier, with no preamp stage in between, removing one extra layer of components. The 12V trigger lets you have an amp be automatically triggered to turn on when the DAC-2 is turned on as well, and the 12V input lets you automatically turn the DAC-2 on into HT Bypass mode. In this way, you can place the DAC-2 between your home theater receiver or processor and your amplifier, allowing you to run a two channel digital system with your home theater system. This might be a feature that many people won't use, but for me it allowed me to bypass my receiver, which was introducing extra noise into the signal, and get the best sound quality possible out of the DAC-2. I also used the HT Bypass for an analog input with the Squeezebox Touch, allowing me to quickly change between inputs and compare the sound from its internal DAC's to those in the DAC-2 without any other equipment possibly influencing the sound.

For the majority of my home listening, the DAC-2 was feeding a Wyred4Sound STI-500 integrated amp or an Onkyo receiver that was connected to an Emotiva UPA-5 amplifier. My primary digital source was a Squeezebox Touch over Coaxial, but I also tested an Oppo BDP-83 over Coaxial and Optical, and a Sony SACD changer over Optical. For computer listening, audio was provided over USB through Foobar using WASAPI exclusive mode control in Windows 7, with all files ripped losslessly to FLAC. The DAC-2 was connected in all possible ways in the main system, testing both 12V triggers and the digital volume control with a direct amplifier connection, as well as in fixed mode.

For the STI-500, I ran the left and right preouts from the Onkyo into Input 5 on the STI, and then used the STI to power the front channel speakers. Since the Onkyo lacks a 12V trigger, I had to program my Logitech Harmony to turn the STI off and on, and set it to the correct input. Later on I had a Pioneer VSX-32 receiver in place of the Onkyo, which has a pair of 12V outputs and made using the STI much easier. I could have the Pioneer trigger the 12V outputs, which would turn on the STI and set it to the HT Bypass input automatically. When the Pioneer was turned off, the STI was turned off automatically and it was as simple as a setup could be. I would usually connect the DAC-2 by XLR inputs to the STI, but also ran the RCA outputs to make sure to test it in all possible configurations.

In Use

My review unit of the DAC-2 was delivered to my office, so I decided that the best way to being my testing then was with the USB input from my computer. Once connected I was prompted to install a device driver to support the 24-bit/192 kHz sample rates over USB, and then I connected the DAC-2 with RCA cables to my NuForce HDP headphone amplifier, which was driving my AKG K701 headphones.

I went straight to the track that initially showed me the strength of the NuForce, "Teardrop" from Massive Attack's Mezzanine album. I quickly heard more of a difference from the HDP's DAC than I had expected to. The DAC-2 had a quieter background, and more distinct bass than the HDP had presented. The strong bass notes during the song had far more weight and authority to them through the DAC-2 than the HDP, letting me know that the HDP wasn't letting me down as an amplifier but the DAC-2 was getting that extra bit of detail out of the music.

One of the main benefits of the DAC-2 is the ability to play high resolution music from companies like HD Tracks, 2L, and Reference Recordings. All of these companies have some demo tracks available to download that range from 24/96 to 24/192 sample rates, and even 24/352.8 WAV files. The HDP can handle up to 24/96 resolution files, but I had not had a chance to listen to 24/192 music until now. I began with the track "Beethoven: Sonate 32 - Maestoso" performed by Tor Espen Aspaas from 2L. Since this is a solo piano work, and that's the one instrument that I ever learned to play reasonably well, I knew how a piano should sound, and can listen for how the DAC-2 represented one. The DAC-2 did not disappoint, rendering the notes from the piano with clear precision.

I find soundstage to be hard to evaluate on headphones, but detail much easier to pick apart, and the DAC-2 was shining through in this regard. I listened to some of the sample tracks from HRx that are recorded at 24/176.4, and once again the detail that the DAC-2 could bring out was stunning. The HRx titles from Reference Recordings are not music that I listen to often, and so I don't want to read too much into tracks that I'm not as familiar with, but it made me long for the day when all music that I purchase will be at the same level as the studio master in fidelity. Large orchestras were rendered with more clarity than I had heard; letting the individual performances shine through instead of being lost in a cloud of muddled sound. It opened my ears up to the possibility that my previous lack of enjoyment in some music might be due to the fact that recordings have not been able to convey the power and scope of the music properly.

Moving the DAC-2 home to my main system, I was surprised at the initial difference that I heard. While listening to Fake Plastic Trees from Radiohead, I switched back and forth between the DAC-2's output and the DAC inside of my Squeezebox Touch that was providing the digital signal for the DAC-2. What I heard was a large difference in how the guitar sounded, but it was a difference that I hadn't expected. The Squeezebox sounded a bit brighter and sharper, which at first you could easily assume to be additional detail that was coming through. As I continued to listen, it was actually the DAC-2 was more accurate and detailed, with a far smoother, more natural sounding guitar. Whereas the Touch was a touch harsh and metallic after the note was struck, the DAC-2 rendered that note and it's decay far more faithfully, sounding more akin to a real guitar and not to a recording of a guitar. It made music far less fatiguing to listen to, as that harshness would tire my ears after a while.

The soundtrack to The Piano from Michael Nyman is a recording that I come back to all the time for it's pure, solo piano work and wonderful music. Listening to "The Heart Asks Pleasure First", I didn't just hear the notes from the piano, but far more than that. I could hear the weight with which the notes were being struck, and the full body of the note as it hung in the air. The best description I can give is to comparing the sound of my stereo without the DAC-2 to that of a Viewmaster, and with it to an actual 3D environment. Without the DAC you can see the width of the soundstage, and see that notes are coming from a certain location and depth, but they just exist at that point. With the DAC-2, there was a fullness and body to the notes, taking them from a 2D point to a full bodied, 3D representation. Removing it from the chain made this soundtrack sound thin, harsh, and less natural than with it being involved. I have found that past components have affected my soundstage before, causing it to shrink or expand in depth and width, but never one that gave it this added dimension of weight.

I really began to cement my impressions of the DAC-2 and it's sonic signature while taking in the recently remastered version of Abbey Road from The Beatles. On "Here Comes the Sun", George Harrison's guitar extended out beyond my left speaker with the DAC-2, and the notes were more distinct, with less blurring into the other activity in the recording and smaller details becoming apparent that I had overlooked before. With the Touch alone the guitar was firmly anchored to the left speaker, refusing to extend beyond its physical boundaries. On "Come Together", John Lennon's vocals sounded less strained than they had before, the DAC-2 removing those harsh artifacts that previously would cause fatigue as the time went by. Now I could hear what Lennon's voice sounded like during the recording and enjoy album after album.

The most impressive material I listened to was Neil Young's Live at Massey Hall album, which includes a DVD with a 24/96 stereo PCM track. This live recording brought out all the details from the concert, with the sound of his piano on the stage, the acoustics of the concert hall, and the reverberation of the notes in the open space. It sounded more like I was on stage at the show than any previous concert recording that I had listened to and it just sucked me in. Making you forget that you're listening to a recording and that you are hearing the musicians live is the ideal goal for any system, and the DAC-2 helped to bring my system closer to that goal than it has come before.

Typically I would round out my listening experiences with the issues that I encountered with the unit, but with the DAC-2 I was drawing a blank on what I ran into. The main issue I encountered is that the Wyred 4 Sound DAC's and integrated amplifiers share common remote codes, but I got around this by disabling the DAC-2's remote in the menu, and this is a problem that very few people are likely to run into themselves. I additionally had the DAC-2 and the Oppo encounter a locking error when listening to Neil Young over Optical, but this didn't happen over Coaxial, or over Optical from the Touch or SACD changer, and so I'm assuming it was just a fluke occurrence that should not typically be an issue.

As far as the STI-500 is concerned, I have nothing but positive things to say about it. Over all the reviews that I have done for Secrets over the past years, I've discovered that the component that has made the most impact on my system is the preamp or receiver. Speakers, CD players, Blu-ray players, amplifiers, and DACs have all made significant impacts, but the brains of the system really affects everything that goes through the system. Using the STI in a HT bypass mode made this easy to compare, as I could hook the DAC up to a receiver and the STI simultaneously. As both were using the same amplifier and speakers, I could switch between inputs on the STI quickly to see the difference in sound quality between a receiver and the STI.

Honestly, it didn't take much comparison to see a clear difference between the two components. The noise floor in the STI was far, far quieter than either the Onkyo or Pioneer receivers. With no music playing, the STI on its own was dead quiet but the Onkyo and Pioneer both had a bit of a hum in the background. This could be due to the amplifiers running in the receivers and some of that electrical noise getting into the preouts of the receiver, but it was clearly there. When actually playing back music, the STI brought about far more clarity between instruments and voices in anything I listened to. Soundscapes where all the instruments would typically blend together were now a collection of distinct sounds, letting your isolate the individual components and pick out details that you had not heard before.

The amplifier section of the STI-500 was quick, detailed, and very accurate to my ears. My Mythos STS speakers are not the hardest load for an amplifier to drive, but the STI really let them shine, with lightning fast responses when musical sections demanded power, and very detailed mid-range and highs. I would not describe the STI as being warm sounding, as it was very clear and accurate, but perhaps a touch dry for someone that enjoys the warm sound of tubes or vinyl. If paired with a speaker that has a bit of a warmer sound, then this sound of the amp might be colored over a bit. In my own use I really enjoyed all of the extra detail that was coming out of the speakers and never found the sound to be fatiguing or piercing to the ear.

This also affected the performance of the DAC-2. When comparing the DAC-2 to the Squeezebox Touch on either of my receivers, it was always in favor of the DAC-2, but it wasn't always a runaway decision. When comparing them both using the STI-500, the DAC-2 was far and away the winner, and so it was the platform I used for the majority of my DAC-2 listening. Extra detail that the DAC-2 could pick out of the music was often glossed over, or muffled by background noise, when using either of the receivers, but that detail shined through on the STI-500. I'm not saying that you shouldn't listen to the DAC-2 if you are playing it with a receiver, but that as the rest of your system improves, the DAC-2 has that detail and resolution to grow along with it.

On the Bench

Since the STI-500 is a fully balanced amplifier, I was unable to test it on my equipment, as it does not support measurements on those devices. For the DAC-2, all measurements were done at 16/44.1 resolution as the current measurement software has an issue with Windows 7 at rates higher than that. The output signal was the optical output from my computer.

At 1 kHz, the THD+N numbers for the DAC-2 were very low at 0.00448% with only one noticeable peak at 3 kHz that was over 85dBV below the peak frequency.

Moving on to a 10 kHz signal, the THD+N drops down to 0.0012%, with over 100 dBV between the peak frequency and the closest peak.

On the 19 kHz, 20 kHz IMD test, the IMD number is very low at 0.0025%, and the peaks are again over 85 dBV above the lower peaks.

On 60 Hz, 2 kHz, the IMD number stays very low at 0.0058%, with side peaks at 4 kHz and 6 kHz, each more than 80 dBV below the main peaks.

On 60 Hz, 7 kHz, IMD is almost identical at 0.0059%, with a side peak at 14 kHz that's around 85 dBV below the main peaks.

The frequency response of the DAC-2 is basically flat out to 15 kHz, and then has a very slow and gradual roll-off of around 3db out to 20 kHz.

Overall, the DAC-2 has posted fantastic results on the bench.

Though I was not able to test the STI-500 myself, Wyred4Sound was nice enough to run the unit through their Audio Precision test device using the same specifications that we would use for our own testing, though we were not able to witness the testing ourselves.

With 5V output for a 1 kHz sine wave, the STI-500 measures around 0.01% of THD+N at both 4 and 8 ohms.

Moving up to 20V output, the THD+N doubles on the 8 ohm load and triples on the 4 ohm load, but the secondary peaks are still 70 to 85 dBV below the 1 kHz peak.

The frequency response at 5V has a slight roll off of around 0.3 dBV from 20 Hz to 20 kHz at 4 ohm, and a roll off at 8 ohm that is the same, but flattens out at around 20 kHz.

At 20V of output, the frequency response roll-off looks to be almost identical as at 5V.

Here we see the power output into 4 and 8 ohm loads graphed against THD+N. For most of the output range it stays below 0.01%, with the knee in the graph occurring right around 0.03% for both loads.

In these two graphs (the first is 8 ohm, the second is 4 ohm), we see that at 8 ohm, the THD+N is flat out to 1 kHz, then there is a rise from 1 kHz to 10kHz where the THD+N triples, then goes back down to its original level by 20 kHz. With the 4 ohm load, the THD+N starts to rise by 30 Hz, cresting at 5 kHz, and then falling from 10 kHz down to 20 kHz, with a peak value that is close to 10 times the THD+N numbers at 20 Hz. However, even these peak numbers are still fairly low at under 0.035% THD+N.


I'm one of those people that have moved to having most of my music library stored in a lossless format on a server for quick access to everything. I love the convenience of it, but usually found that for really critical listening I would go back to playing the physical CD. With the Wyred4Sound DAC-2 I no longer felt that I needed to have the CD in the player to get the best possible sound. Music took on an extra dimension that it did not possess before, and was more relaxing and enjoyable to listen to for long periods of time. Installation into my system was transparent and once it was configured I never needed to go back and change anything at all on the DAC-2, allowing me to relax and enjoy the music.

I did notice the benefits of the DAC-2 far more when it was connected through the STI-500 or directly to the amplifier itself. Running it through a receiver caused a bit of loss in the detail, and the differences between the Touch and the DAC-2 were far more subtle. This made the flexibility provided by the HT Bypass mode all the more important, as it lets more people get the full benefit out of the DAC-2 by skipping over a weaker link in the chain. The performance of the pair was so wonderful as a stereo setup, that I actually reconfigured all of my other components (TiVo, Oppo BDP-83) for stereo mode, hooked up their analog outputs to the STI-500, and enjoyed a pure stereo system instead of a multichannel system for a couple of weeks.

For someone that is looking to get high quality music playback from their PC, or looking to take an existing digital component to the next level, the DAC-2 comes highly recommended. It supports all of the current high resolution material out there, integrates easily, and will be able to continue even if 24/192 music becomes the new standard. If you are looking to get the highest quality stereo performance out of your multichannel system, or just want a high performance integrated amplifier for your stereo setup, then I would certainly put the STI-500 on the list of components to audition as well. It has the power and control to drive any speaker you might have, and all the inputs and features you could ask for.