Empirical Audio Overdrive SX Ethernet DAC/Pre

Overdrive SX Ethernet DAC/Pre
Device Type: Digital to Analog Converter
Digital Inputs: Ethernet: Up to 24bit, 44.1, 48, 88.2, 96, 176.4, 192 kHz; S/PDIF Coax Canare 75 ohm BNC - up to 24/192 kHz, I2S (Empirical standard RJ-45) up to 24/192 kHz
Output: 1 Pair RCA (Unbalanced) and 1 Pair XLR Balanced
Dimensions (H x W x D): 2.5 inches X 6.75 inches X 6.75 inches
Weight: 3.11 pounds

Substation SX AC Power Supply: (IEC AC Connector)
Dimensions (H x W x D): 2.5 inches X 6.75 inches X 6.75 inches
Weight: 2.9 pounds
Price: $12,995 (Overdrive SX DAC and Substation AC Power Supply)

Availability: Direct Sales
Website: www.empiricalaudio.com

The Empirical Audio Overdrive SX Ethernet DAC/Pre represents Steve Nugent's most current thinking on DAC design. Steve, chief designer and owner of Empirical Audio, has been building Empirical Audio DACs since 2009. His engineering background and experience in digital design have served him well having come up with many original creations and unique approaches in DAC design. The Overdrive SX builds on the basic design of his Overdrive SE, a DAC I reviewed for AudioStream back in 2014.

Many key design elements have been preserved in the Overdrive SX from the SE version. The aluminum casework of the DAC and Substation AC power supply with their well vented appearance and top mounted heat sink are impressive looking and visually suggest a high-performance product. The Overdrive SX utilizes a small chassis size for short digital and analog signal paths to reduce noise from ground-plane coupling and crosstalk. An AC-coupled output is also included because DC-coupling would not allow pure Class-A operation.

Perhaps the greatest difference is the Ethernet input that replaces the USB input of the older SE version. The Overdrive SX can be ordered with a USB input to replace the Ethernet module for those that prefer USB.

I asked Steve to discuss the changes in the Overdrive SX from the older SE model:

The visible difference is the Ethernet interface (input) which replaced the USB interface and a new volume knob with diamond insert, as well as a ground wire in the power umbilical.

It is still optional to have a USB interface rather than Ethernet. It is also a new USB module, with galvanically isolated XMOS interface.

The other internal physical changes include:

Duelund output capacitors
This replaces the previous combination of capacitors with a single capacitor for each channel. The result is, in our opinion, a more coherent stereo image. The original capacitors are still optional at some cost savings.

Improved linearity of the output driver compensation circuits
This makes the output drivers behave more ideally, like excellent vacuum tubes or JFETs, while still maintaining the liquid smoothness of bipolar transistors, which we prefer over the sound of JFETs or MOSFETs.

Improved power decoupling on many circuits for better dynamics, linearity and lower jitter
This improves dynamics, jitter and lowers distortion. Direct measurements of our stand-alone Ethernet interface, the "Interchange" which uses the same Ethernet module, shows jitter of ~15psec at the end of the S/PDIF coax cable. Because the Ethernet module is directly interfaced with I2S inside the Overdrive SX, we expect the jitter to be even lower. Our listening tests seem to confirm this. It is not possible to make an accurate direct measurement inside the DAC. For jitter measurements, we prefer to make these directly on the digital signal with a GHz bandwidth scope, as we have found this to have a better correlation to sound quality. We have published many of these measurements on our forum.

Some power devices were relocated for better cooling
The Ethernet interface draws significantly more power than the USB interfaces so we moved 2 more devices to the top heatsink for better cooling. Since virtually all circuits run Class-A inside the Overdrive SX, it tends to run warm.

Substation power unit improvements
These include a different power sequencing scheme as well as more voltages being pre-charged to avoid arcing of the main relay thus preventing degradation of the contacts over time.

We chose Ethernet as our new reference interface for several reasons:

  1. It does not have the burden of needing custom drivers to be issued for each new operating system for Linux, Mac or Windows. Even our XMOS USB implementation requires a driver for Windows.
  2. We have found that USB requires the customer to jump through more hoops to optimize many variables to achieve exceptional sound quality. These variables include USB output port quality, USB cable quality, computer or server power supply quality, playback software versions, background tasks running on the OS and different OS's, and maybe other variables. Any of these can impact sound quality with USB. It's not that USB cannot sound great, it's just more difficult to get there. Not that Ethernet is without hoops, but there are fewer roadblocks to good sound quality. The router power supply and how it is grounded to earth-ground and the Ethernet cable quality still seem to matter, but these don't make a huge difference and it is not necessary to purchase expensive solutions to get stellar results.
  3. Given identical implementations and clocks for Ethernet and USB modules, we have found the Ethernet to deliver a better rendering of very high-frequencies. Our XMOS USB sounds very similar for vocals, midrange and bass, but for the highest frequencies of rain falling, percussion, guitar, wind sounds and footsteps, Ethernet tends to be more live sounding. Since the implementations are almost identical, we can only speculate that the data is somehow being altered during playback by DSP or other manipulation with USB. Since different playback software for USB sounds different, and even different versions of the same software sound different, it's hard to believe that something is not changing in the playback process.
DAC chip used in the Overdrive SX
The D/A chip has not changed from the SE. It is an Analog-Devices Delta-Sigma chip. We found by testing several different D/A chips that majority of them can be configured to sound great (there are a couple of exceptions), so selecting the best one is not just a matter of picking the latest technology or even the best distortion or S/N specs. This chip was chosen because the reference voltage can be adjusted to control output volume and the digital filters are selectable rather than defaulted, and of course, because it was musical. Making most D/A chips sound great is a function of implementation and optimizing power delivery, not just choosing the latest technology chip. Because we can select the digital filter with this chip, we can essentially make this Delta-Sigma sound a lot like a NOS R2R DAC, but also supporting hi-res files and delivering clear, fast high-frequencies, which is usually the deficiency in R2R. We get the step-size accuracy of the Delta-Sigma combined with a non-invasive digital filter that is better than an apodizing filter and mimicking the R2R. There is very little pre or post ringing and the impulse response achieves the maximum voltage applied. As a result, the DAC delivers very accurate transients, even at the highest frequencies; attack and decays that are natural and live-sounding. Echoes of the venue walls are revealed that give you a real sense of the venue size and shape.

Simplicity in Function
The Overdrive SX was relatively easy to set up given that there are just a few external controls on the panels of the power supply and DAC that need to be addressed. There is a power switch on the front of the Substation power supply that provides DC to the Overdrive DAC. 3 LED indicators display the 3 DC voltages supplied to the DAC. When the power switch is off, only the Substation is powered with no DC output.

A toggle switch on the DAC selects from the 3 inputs while another toggle switch selects from Low, Medium, and High frequency digital filter roll-off. The High is the down position and is the recommended filter. A De-emphasis toggle switch applies an equalization at the high-frequencies that eliminates hardness due to high-frequency pre-emphasis in some recordings. The down or Normal position is recommended.

There are 2 recessed switches; one allows High/Low gain. The other selects the volume control In or Out. Two Volume Range jumpers are also provided and are located just inside the front panel to optimize the operation of the volume control. 3 LEDs indicate USB operation, Data flow, and DC power.

The Volume Control is designed to provide best performance when at near maximum position.

Associated Components and Software Used in the Evaluation of the Overdrive SX

I utilized my Asus G701VI laptop running Windows 10 Pro 64 (Version 1709) in a dual boot configuration with a standard Windows version on one partition and another partition with AudiophileOptimizer 2.20 beta 6. The Asus G701VI possesses an overclockable Intel Core i7 6820HK processor with 32 GB DDR4 2400Mhz SDRAM and a very fast PCIe Gen3 X4 NVMe SSD. This laptop has 3 USB 3.0 ports as well as a Thunderbolt port (USB type- C). An NVIDIA GeoForce GTX1080 with 8 GB VRAM processes video. This powerful video processor allows significant CUDA offload processing for the Signalyst HQPlayer. The Asus laptop was plugged into a Shunyata Research Hydra DPC-6 v2 distribution center to firewall the noise generated by this computer from contaminating my AC line.

The Asus was placed on a Synergistic Research Tranquility Base UEF grounded with the Synergistic Research High Definition Ground Cable / Grounding Block as was the computer.

A G-Technology 24 TB G|RAID Thunderbolt 3 / USB 3.1 drive was connected to the Asus. The G|RAID Thunderbolt drive was powered by an HDPlex 200w linear power supply plugged into a Shunyata Denali 6000T power conditioner. The G|RAID Thunderbolt drive and its HDPlex power supply were placed on a Synergistic Research Tranquility Base.

The music software used for the Overdrive SX evaluation was JRiver Media Center 23 (64-bit version). The Overdrive SX, a DLNA device, works with JRiver and Audirvana Plus for OSX. JRiver Media displayed the Overdrive SX as an Audio Renderer with music files played back from a playlist.

The Overdrive SX was plugged into a Shunyata Research Triton v3 with a Shunyata Sigma NR AC cord.

An AudioQuest Vodka Ethernet cable was employed for the Overdrive SX input from an AQVOX SE modified switch.

Initial Musical Experience

I connected the balanced output of the Overdrive SX to my Ayre KX-R Twenty preamp. Steve feels that using the balanced output will result in superior sonic performance. The Overdrive SX is limited to 24 bit, 192kHz, which turns out not to be much of a limitation for this user. It didn't take long for me to conclude that the Overdrive SX is a very special sounding DAC.

The Overdrive SX puts out an enormous wide soundstage with excellent depth perspective. This DAC also reproduces a sense of image height, no doubt, only limited by my Wilson speakers. The Overdrive SX DAC is very revealing from top to bottom and is superb in resolving inner detail with a lifelike presence in both timbre and dynamics. The Overdrive has extremely low noise and overall coloration. The sonic signature of the Overdrive SX is a slightly darkish overall balance that never truncates or blunts transients. The low end has good grip, definition, and impact that will truly entertain audiophiles who possess a dynamic system.

The Overdrive SX tends to have a more distant perspective when reproducing musical instruments and voices. This is not an in-your-face presentation, but a relaxed natural sound that is very engaging over the long haul.

In terms of general use, the Overdrive Substation power supply and DAC get quite warm-so forget about stacking these two units upon each other. I also recommend that users should leave good ventilation around the power supply and DAC for optimum performance.

In discussions with Steve Nugent, I found that he was concerned that his Ethernet Overdrive SX might suffer sonically from poorly implemented Ethernet or Wi-Fi solutions. Steve provided me an early design of his Wi-Fi interface that was quite easy to set up. I must admit that the Empirical Wi-Fi product sounded as good or better than my more complicated Ethernet setup; an Asus Media Bridge (RP-AC68U) that feeds a TP-LINK MC200CM Gigabit Media Converter, Tripp Lite Duplex Multimode 62.5/125 Fiber Patch Cable (SC/SC) fiber cable connects to another TP-LINK MC200CM Gigabit Media Converter, and this to an AQVOX SE switch. All powered by linear power supplies and connected to a Shunyata DPC-6 v2 power conditioner.

How Good is the Volume Control?

I connected the Overdrive SX directly to my Ayre MX-R Twenty power amps with balanced cables. The sonic result was quite good and should satisfy most users unless they own a very fine preamp. I did find that my Ayre Acoustics KX-R Twenty preamp ($27,500.00) did outperform the Overdrive's direct volume connection by presenting a fuller sound with more weight. But I recommend using the Overdrive SX direct-to-amp connection if one doesn't need a preamp for multiple input sources.

I reprinted Steve's explanation of the volume control design from my 2014 Overdrive SE review:

"No one would disagree that the best performance will be achieved when the line-out of a DAC is directly connected to an amplifier. This of course is hazardous with the typical DAC and requires the use of DSP software volume control to reduce the volume. Speaker damage is obviously a concern with this technique, as well as bit decimation. The Overdrive uses a volume control technology that connects the line-out directly to the amps, but uses the D/A conversion reference voltage to reduce the volume rather than DSP. The reference voltage is the voltage that is used by the D/A to generate the height of the stair-steps that make up the analog output waveform. There are no other devices or gain stages added or being changed with volume adjustment in the Overdrive. One gets the benefit of direct line-out to amp connection without having the hazards or the decimation that occurs with DSP software volume control. This volume technology is unlike all other techniques in that it reduces distortion levels as the volume is decreased. This is exactly what one wants from an ideal volume control. Direct amplifier connection is what we recommend."
Comparisons

How does the Overdrive SX compare to my reference, the Ayre Acoustics QX-5 Twenty? I listened with JRiver Media Center 23 for both DACs in a similar software setup. Sonically, these two DACs sound quite different from each other. The Ayre has a more forward presentation presenting images in the front plane of the speakers while the Overdrive SX tends to portray the same images behind the front plane of the speakers. The Overdrive has similar soundstage width when compared to the QX-5, but the depth seems larger and easier to discern with the Overdrive SX. Both DACs are fast sounding with excellent transient response, but the Ayre has a little more punch to the bass. Just which one is best sounding is going to depend on one's personal taste and associated components. I found both the Overdrive SX and the Ayre QX-5 Twenty to be among the best DACs I have experienced, each possessing their own sonic signature.

Music

Stacey Kent's release I Know I Dream-Orchestral Sessions (44.1/24) not only had wonderful image stability and pinpoint focus of her voice, but was extraordinarily expressive and involving listening to the Overdrive SX. The orchestra backing Stacy had an open and airy sound that was harmonically rich with extended treble with no harsh edge.

Listening to Reference Recordings' Michael Stern conducting the Kansas City Symphony performing Adam Shoenberg's American Symphony (24/176.4) was a real treat when heard with the Overdrive SX. I found that this is a magnificent orchestral recording with great bloom and three-dimensionality to the sound. The Overdrive reproduced a richly layered soundstage with wonderful tonal naturalness. The inner detail and resolution of this recording was lifelike with excellent dynamic life and detail.

The Overdrive SX's pure realism was displayed listening to Eric Bibb's Migration Blues (24/48). Eric's voice and guitar emerged from a black-velvet background with immediacy and palpability. The backup instruments sounded real with tonal colors that were rich with excellent resolution of transient detail. Perhaps the most impressive feature of the Overdrive SX was its ability to allow one to get lost in the music with its vanishingly low noise and coloration.

Conclusion

Steve Nugent has designed a first-class sounding DAC that I found to not only be transparent and revealing, but musically engaging as well. I also liked the ability of this DAC to act as a preamp when driving my amps directly. While I didn't find the inability of this DAC to directly play DSD files to be a major shortcoming, I hope that the Overdrive SX will become Roon Ready in the near future. For those audiophiles looking for something special in appearance and sound, the Empirical Audio Overdrive SX deserves your consideration.


Associated Equipment

COMMENTS
bobflood's picture

Great Review!

Thanks,

Bob

Steven Plaskin's picture

Thanks for checking out my review Bob,

Steve

Bob Parish's picture

Are you kidding me?

Al Moritz's picture

Why DSD? PCM is all you need.

My Schiit Yggdrasil also decodes only PCM. I applaud manufacturers who do not put extra effort and money into a format that I am not interested in, only because a minority of users crave for it. Had my DAC incorporated DSD, with a concomitant price increase, I might not have bought it.

Apparently there are many who think the same way as I do, since Schiit gear sells like hotcakes. I wish also Steve Nugent well with his product.

Bob Parish's picture

I'm sorry, but PCM is all I need for don't listen to music. I'm tired from PCM fatigue sound since CD begining in the 1990's...
I'm audiophile for MORE than 40 years with almost US$100K invested in high end stuff, and after listen to HQPlayer upsampling to DSD512, I WILL NEVER MORE LISTEN TO PCM DIRECT! NEVER!
If you didn't try this, you really don't know what you are saying.
If you want details about my settings, try here: http://www.theabsolutesound.com/articles/oppo-digital-sonica-network-dac/

agb's picture

Reading some of Lavorgna's copy it appears we share the same taste in music. I have an earlier Stacy Kent album...excellent. And almost all of Bibb's. He's as good as they come. As a kid Eric had Bob Dylan visit his home once and taught him a few licks. And Dylan taught me Travis picking in Washington Sq. Park. May I recommend the entertaining Bibb with Habib Koite album? And Blues Singer too. Running now to buy that Migration Blues CD - yes, it's that good on Amazon's preview feature.

Michael Lavorgna's picture
...you share the same taste in music as Steve Plaskin, the guy who wrote this review ;-)

A few months ago, we changed the layout of the main page to try to highlight the writer whose name appears directly under the article title. Perhaps we need to reexamine this issue. I'd appreciate any recommendations you may have as to how we can make the author more obvious.

Cheers

Steven Plaskin's picture

I have the Bib album with Habib Koite; Brothers in Bamako.

Good stuff!

Thanks for your suggestions,

Steve

agb's picture

Evidently Plaskin has very good taste in music, as well as good ears.

It was my bad eyes that made me miss the author of this review. Apologize for it. I have no suggestion for making the names more prominent - that is a coding issue. Thanks for the replies guys.

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