The Chord Electronics QBD76HD is a very unique digital to analog converter to say the least. The QBD76HD is one of a handful of distinct DACs designed around FPGAs rather than a mass produced silicon DAC chip. Externally the QBD76HD is just as unique with a rock solid aluminum enclosure and a simplistic yet sophisticated industrial design audiophiles have come to expect from Chord. Tying both external and internal design together is a one-of-a-kind large glass porthole that enables a blue LED lit view of the inter-workings of the QBD76HD. In addition to its unique design the QBD76HD has a unique sound that ranks right up there with some of my favorite DACs.
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The Chord QBD76HD DAC of Distinction
Love it or hate it the Chord QBD76HD looks like no other DAC. It's small frame just 13.3" wide x 2.4" high x 5.7" deep enable placement in many more locations than traditional DACs. The DAC's 15.4 lbs. weight is comprised mainly of its beautifully finished aluminum enclosure. During the review I opened the top of the unit to swap chips and was pleasantly surprised to see very thick walls on all sides of the QBD76HD. I'd assumed there would be minor corner cutting or thinning of the aluminum somewhere. I was fortunate to have both the black and silver versions of the QBD76HD in for review. I prefer the silver version because the light color allows one to see the detailed metal work with curves and cut-outs much better than the anodized black version.
The QBD76HD contains two glass portholes. The small porthole allows the user to view an informational display for items such as buffer size, input selection, and sample rate. The much larger porthole is less informational to the untrained eye. Nonetheless the large opening displays a nice looking internal design that inspires a certain pride of ownership. Surrounding the large porthole are little blue LED lights that illuminate the inside of the DAC as well as emanate a surreal blue light into one's room. When projected on the ceiling of my dark listening room the blue light produced dreamlike clouds. For the most part I liked the effect of the blue lights. Unfortunately there is no way to disable the lights. Users who love the sound of the QBD76HD but dislike the light show may be forced to hide this distinctive looking DAC in a breathable cabinet to stop the light from entering the listening area.
Internally the Chord Electronics QBD76HD DAC is all about Field Programmable Gate Arrays (FPGA). In layman's terms an FPGA is like a blank digital canvas that allows engineers to program any function into the chip. Chord uses FPGAs to gain flexibility in design and to distinguish itself from most other high end companies. The QBD76HD contains a Xilinx Spartan 3 FPGA, with 1.25 million gates. Everything digital in this DAC is done via FPGA. For example switching of SPDIF inputs, all digital SPDIF decoding, digital PLL, RAM buffer controller, WTA filtering, and the 5th generation Pulse Array DAC are all FPGA controlled.
Chord is on the 5th generation of its Pulse Array DAC. Among the improvements to this version of the delta-sigma DAC are the noise shaping and jitter reduction capabilities. DACs use noise shaping to reduce noise in the audio band. The Pulse Array DAC uses 8th order noise shaping. This is higher than any known DAC according to Chord. Jitter reduction in the QBD76HD is done via a digital phase-lock loop (PLL) as opposed to more conventional analog PLLs. Chord specifically addresses data related jitter with this digital PLL and avoids the distortion and noise of an analog PLL with this design. Readers should note this PLL design is only used for the traditional S/PDIF and AES inputs.
The QBD76HD also contains a RAM buffer. Such a buffer has been the subject of countless Internet discussions with many armchair engineers suggesting a RAM buffer is the panacea to all digital problems. A button on the top of the DAC allows the user to select No Buffering, Minimum Buffering, or Maximum Buffering. According to Chord, "This RAM buffer sequentially takes all the data, retimes it, and sends it out. The RAM buffer allows the jitter free local clock operation without needing to send back a clock signal to the data source." That said the DAC does offer word clock output to send clock to a device such as a Lynx AES16 or Merging Technologies Mykerinos card. Maybe this is the belt and suspenders approach. During the review period I discovered one annoying issue when using the RAM buffer at its Maximum setting. I warmed up to the fact that playback is delayed by about three seconds after selecting play while the buffer is filled. However when switching between tracks of different sample rates such as from 24/96 to 24/192 with the buffer set to Max the first two or three seconds of the next track are completely skipped. It sounds as if the buffer is filled, but playback starts without the initially buffered data. I adjusted several settings within JRiver Media Center such as pausing playback for a few seconds when switching sample rates so the DAC's clock has time to lock in the new rate. The QBD76HD locks in on the new rate very fast anyway, but I wanted to eliminate all possible causes of the issue. I found the only way to hear a complete track including the first few seconds when switching sample rates is to set the QBD76HD's buffer to zero. One work around is to restart the new track once playback begins as the restarted track will keep the sample rate already set in the DAC. This buffer issue isn't a showstopper for me. I'm fairly sure Chord can adjust its on-board software to eliminate the issue if it's reproducible in the Chord test lab.
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The Chord QBD76HD Inputs of Distinction
The QBD76HD wouldn't be a Chord product if it didn't contain a unique twist on its inputs. Chord is one of a few DAC manufacturers who require dual wire AES. Dual wire AES requires two AES/EBU cables from a transport or sound card for 24/176.4 and 24/192 playback. Sample rates at 96 kHz and below function fine with only a single wire connection. Requiring dual wire AES is a design decision based on performance. The manufacturers with this requirement have waived the convenience of a single wire connection because they believe performance gains can be had with two wires. I've discussed single versus dual wire a few times with different engineers. Some say this is a gray area and dual wire is really the way to go for ultimate performance while others suggest the Audio Engineering Society has all but concluded single wire is sufficient.
One configuration I've never seen is dual wire TosLink. The QBD76HD manual specifies dual wire for 176.4 and 192 sample rates even via TosLink connection. I don't know how one would configure this using consumer hardware such as any PC with two optical outputs. I'm guessing this is more of a professional specification.
There are two 75 ohm BNC coaxial S/PDIF inputs on the QBD76HD. The BNC connector is capable of a true 75 ohm connection, unlike RCA and XLR connectors, and is preferred by many engineers and consumers. If nothing else the locking BNC connector is much more desirable than the more common and sometimes problematic RCA connector. At the end of the review period I tested the coaxial inputs on both Chord QBD76HD DACs I had in-house using a Berkeley Audio Design Alpha USB to feed a digital audio signal. According to the user manual the QBD76HD is capable of sample rates up through 192 kHz over a single coaxial S/PDIF connection. According to my tests the QBD76HD has trouble with higher sample rates via coaxial S/PDIF.
Black QBD76HD Without Chip Upgrade
Bottom Coaxial S/PDIF input: Display indicated Lock during playback of 176.4 and 192 kHz material. The display never indicated the sample rate as it should and sound was never produced out of the analog outputs. Thus playback of 176.4 and 192 material via single coaxial S/PDIF wire didn't function.
Top Coaxial S/PDIF input: Display indicated Lock during playback of 176.4 and 192 kHz material. The display never indicated the sample rate as it should and sound was never produced out of the analog outputs. Thus playback of 176.4 and 192 material via single coaxial S/PDIF wire didn't function.
Silver QBD76HD With Pre-production Chip Upgrade
Bottom Coaxial S/PDIF input: Capable of playback of 44.1, 48, 88.2, 96, and 192 kHz via single wire without problems. Attempts to play 176.4 material resulted in a barrage of clicking sounds emanating from the DAC. The clicking noise is from the output relays as the DAC struggled to obtain a good digital lock from the output of the Alpha USB. During normal playback there is a single click when the sample rate changes and the clock locks. During playback of 176.4 material the clock was incapable of locking thus producing the very fast clicking heard in this recording done with my iPhone.
Top Coaxial S/PDIF input: Capable of playback of 44.1, 48, 88.2, 96, and 192 kHz via single wire without problems. Attempts to play 176.4 material resulted in clicking sounds emanating from the DAC every 10 to 15 seconds while the music played. The clicking noise is from the output relays as the DAC struggled to obtain a good digital lock from the output of the Alpha USB. These were the same output relay sounds as produced through the bottom input. Here is a recording of playback using the top coaxial S/PDIF input.
Note: According to Chord it has many customers using QBD DACs with 24/176.4 material and the DAC has always worked well. Before publishing this review I used the Musical Fidelity V-Link 192 as a different USB to S/PDIF converter to test the coaxial inputs at high sample rates. I was unable to play 24/176.4 material at all and playback of 24/192 material suffered from the clicking of the output relays while struggling to obtain a digital lock from the V-Link output.
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The vast majority of my listening was done through the QBD76HD's high speed USB input capable of playing PCM audio up through 24/192 and pure DSD audio using the DoP v1.0 standard (chip upgrade required for DSD playback). The original QBD76 DAC contained a Bluetooth input that has been replaced in the HD models with the high speed USB port. Both the HD and non-HD versions of the DAC contain a full speed USB port capable of 44.1 and 48 kHz playback using an inferior adaptive USB transfer mode. The HD version's high speed USB port is differentiated from the full speed USB port by a unique Lemo four pin connector. This Lemo connector fits perfectly in the hole left by the Bluetooth antenna allowing a much simpler upgrade from the QBD76 to the HD version. Chord supplies a Lemo connector terminated USB cable for use with the high speed USB port. I was unable to find a source for USB cables with this unique connector other than Chord. However the Lemo connector can be purchased from Internet sources if any computer audiophiles are brave enough to terminate their own cable.
The high speed asynchronous USB input uses a Cypress USB receiver that hands the data off to a discrete Xilinx CPLD. Chord worked with an Italian USB design team to develop the necessary driver interface but the handling of the USB data is Chord's own proprietary design. The Xilinx CPLD handles all of the clocking and data and switches two crystal oscillators, one each for sample rates based on 44.1 or 48 kHz, to give the correct clock information for the sample frequency.
This async USB input is on an electrically isolated card, replacing the Bluetooth card, that is completely separate from the main DAC circuitry and power supply. The DAC circuitry itself has several layers of power supply regulation and filtering to protect the audio circuit from any induced noise. Each main component such as the crystal clock generator, the op amp output stages and the S/PDIF inputs have their own discrete power supply sections to provide as much isolation as possible.
Custom software / drivers are required to use the QBD76HD on both Apple's OS X and Microsoft's Windows operating systems. A linux driver is currently unavailable.
During the review period I heard a high pitched whine coming from my speakers when listening to the QBD76HD via its high speed USB input. This high pitched whine was fairly quiet but still audible when listening for it but only when playback was stopped. I duplicated the issue with both DACs and both pre and post DSD chip upgrades. I measured the high pitch at 5323Hz when connected via USB to my battery powered MacBook pro and 4887Hz when the DAC was connected to my C.A.P.S. v2.0 server's 
SOtM tX-USB card. Chord attempted unsuccessfully to reproduce this issue and provided measurements taken with an Audio Precision analyzer that display no such noise. I was unable to reproduce the high pitched whine after replacing the QBD76HD with an EMM Labs DAC2X. That lead me to believe the Chord DAC was 100% the cause of the issue. However, after placing the Chord DAC back in my system and changing amplifiers from my Spectral Audio DMA-260 to the Bel Canto ref1000m mono blocks the high pitched noise also stopped. At the direction of Chord I tried several different configurations and was unable to pin down the exact cause. The noise wasn't caused by the DAC alone and wasn't caused by my amplifier alone. I'm willing to chalk this one up to a system incompatibility that an experienced local dealer could probably help resolve.
Here is an FFT graph of the sound coming from my speakers without the Chord QBD76HD high speed USB input connected.
Here is an FFT graph of the sound coming from my speakers with my MacBook Pro running from battery connected to the Chord QBD76HD high speed USB input using the supplied USB cable.
Here is the Audio Precision graph from Chord that displays no noise in the areas I measured in my system.
The Chord QBD76HD A Distinctive Sound
Over the years I've listened to many DACs. A sure sign of a great DAC is one that can keep me from checking my email or browsing CA while in my listening chair. During the entire review period of a couple months the QBD76HD kept me engaged 100% of the time. This DAC has a unique sonic signature that produced great sounding music through my system. The QBD76HD's unique sound is less like the airy Berkeley Audio Design Alpha DAC and closer to, but less vivid than, the dCS Debussy. The readily apparent sonic signature of the QBD76HD is a full mid bass, plenty of slam, and beautiful decay. Listening to Ottmar Liebert's One Guitar at 24/96 through the QBD76HD I noticed the guitar reproduced just a touch thicker than I am used to hearing through my Alpha DAC or I could say the Alpha DAC is a bit thinner. Either way both DAC reproduce Ottmar's guitar wonderfully but different. The full mid bass and punchiness of the QBD76HD was pleasantly audible during Elvis Costello's (The Angels Wanna Wear My) Red Shoes and Watching The Detectives from his The Best of Elvis Costello: The First 10 Years album. I must have listened to the opening of 'Detectives' five times with the volume plenty loud. Not only were the drums impressive but the bass line throughout the track was just as prominent and engaging through the QBD76HD. I really like Elvis Costello's version of Almost Blue but he can't compare sonically to his wife Diana Krall's rendition from The Girl In The Other Room at 24 bit / 96 kHz. Near the 3:25 mark of the track and running through the end is a wonderfully full and deep bass that was worthy of a few replays during the review.
Plenty of bass and transient slam can be heard through the QBD76HD on the Kansas City Symphony's performance of Passacaglia at 24 bit / 176.4 kHz. The bass was deep and controlled, maybe a tad thick for my taste or what I'm used to, but very enjoyable. Passacaglia and Martin Vatter's Walchensee, Mondnacht from the album Klangbilder I in high resolution 24/88.2 both helped this Chord DAC shine when reproducing incredible instrument decay. On Passacaglia the instruments rang out with great decay, hanging on and fading very delicately. On Walchensee, Mondnacht the wonderful decay of the piano's hauntingly deep notes and piercing high notes seemed to hang on and on and on in a very good way. I didn't get the sense that the QBD7HD was memorializing the events in any manner.
Listening to the vocals of Randi Tytingvaag's Red Or Dead I heard a bit more smoothness than I am used to hearing. I prefer her vocals a bit more stern, but the smoothness wasn't enough to detract from the otherwise great reproduction of the other elements of this track. Throughout the track instruments can be heard in the background coming in and out with the bells very prominent. On the track My Heart Belongs To Daddy a similar coming and going of instruments can be heard in both channels. Through the Chord QBD76HD the sounds are very clear, distinct, and the separation of instruments is terrific.
Near the end of the review period I received a DSD capable chip from Chord. I swapped out the chips inside the DAC to enable pure DSD playback using DSD over PCM (DoP v1.0) through the high speed USB input. Pure DSD playback without conversion to PCM was flawless on both Mac OS X with Pure Music and Audirvana Plus and on Windows 7 with JRiver Media Center version 17. I listened to The Blue Coast Collection 1 & 2 from Blue Coast Records in both 24 bit / 96 kHz PCM and 1 bit / 2.8224 MHz DSD. These albums were recorded to analog tape then transferred to DSD. The PCM version was created using Korg's Audiogate (I believe) from the DSD files. Vocals on the PCM version sounded very synthetic compared to the native DSD version through the Chord QBD76HD. The vocals almost sounded like a recreation or Technicolor version of the DSD version. This is most evident when listening to Keith Greeninger and Dayan Kai on Looking For A Home. In addition, the center image on the PCM version sounds like Keith is singing through an orange traffic cone compared to the laid back and much wider center vocal image reproduced with the pure DSD layback of the QBD76HD.
The beauty is the ability to hear this collection in pure DSD like Blue Coast intends it to be heard. This has nothing to do with a format war or PCM v DSD. If this recording was done live to two track at 24/192 PCM I'm willing to bet I'd be singing the praises of the PCM version over a converted DSD copy. Now that record labels and artists are releasing pure DSD recordings it's wonderful to hear these recordings in their native format. The QBD76HD is in a position to playback PCM and DSD over USB without a glitch.
Conclusion
The Chord Electronics QBD76HD is a great digital to analog converter. This DAC is unique from all points of view. Externally the QBD76HD looks sophisticated, simplistic, and modern. The blue LED lights add a touch of "because we can" engineering and I like that from Chord. Its thick, bomb proof, aluminum housing with clear glass porthole exude quality and richness. Internally the QBD76HD is just as unique. Built around custom FPGAs instead of DAC chips produced by the millions Chord will never be accused of copycatting or following the mass market. Chord Electronics ltd. marches to its own drummer as does the QBD76HD DAC with its unique sound. The QBD76HD not only looks great but sounds great as well. I thoroughly enjoyed every piece of music played through this DAC. From fine details at low levels to bombastic transients at concert levels the QBD76HD reproduced it all wonderfully. The Chord Electronics QBD76HD DAC with asynchronous USB input to 24/192 is highly recommended and one of my new favorite DACs.
Product Information:
- Product - Chord Electronics ltd. QBD76HD DAC
- Price - QBD76HD $7,000, QBD76HDSD $8,500 (with DSD option)
- Product Page - Link
- User Manual - Link (PDF)
Associated Equipment:
- Source: MacBook Pro, C.A.P.S. v2.0 Server
- DAC: Berkeley Audio Design Alpha DAC Series 2, dCS Debussy
- Preamp: Spectral Audio DMC-30SS Series 2
- Amplifier: Spectral Audio DMA-260
- Loudspeakers: TAD Labs CR1 Compact Reference
- Remote Control Software: JRemote, Apple Remote
- Remote Control Hardware: iPhone 4, iPad (3rd Generation)
- Playback Software Windows 7: J River Media Center 17, iTunes, Pure Music v1.86, Audirvana Plus
- Cables: Spectral Audio MH-770 Ultralinear CVTerminator Series II Loudspeaker Cable, Spectral Audio MI-350 Ultralinear CVTerminator Series II Analog Interconnects (RCA), Mogami W3173 Heavy Duty AES 110 ?, MIT Oracle ZIII Power Cables, ALO Audio AC6 Power Cables, Wire World Silver Starlight USB Cable, AudioQuest Diamond USB Cable
- Network: Cisco SG200-26 Switch, Baaske MI-1005 Ethernet Isolator, Micro Connectors Augmented Cat6A Ethernet Cable, Apple AirPort Extreme, Cisco RVS4000 Router, Cisco DPC3000 Docsis 3.0 cable modem, Comcast Extreme 105 Mbps Internet Service
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