A Survey of Upper-Echelon DACs
(and Short Block USB Filter)
This is a follow-up to Ed Momkus’s March 2011 review of the Empirical Audio Overdrive DAC, Pace Car Reclocker, and Monolith Battery Supply.
I am one lucky guy: For the past few months I have had the incredible good fortune of evaluating a number of DACs in the $6,000-$10,000 price range. Needless to say that is some serious change, and I approached this with the expectation that all the DACs would all offer outstanding performance. While I didn’t expect them to sound identical to one another, I did expect such differences to be small, wherein each DAC had its own flavor. We’re going to kick off the series with the Overdrive® SE USB DAC/Pre from Empirical Audio, which I will refer to simply as the Overdrive. Thanks go to Merrill Wettasinghe of Merrill Audio, for suggesting that I include the Overdrive in my survey.
The man behind (and in front) of Empirical Audio is Steve Nugent. Steve is an accomplished electrical engineer, and first became known in the audio world for offering modifications to other manufacturers’ products. Steve then sequed into designing and manufacturing his own products, all pertaining to digital audio. Amongst the products Steve has produced are digital re-clockers, and interfaces for devices such as the Sonos and Squeezebox, so as to improve their performance when output to an external DAC. Steve eventually tackled the highest mountain in digital audio, the DAC itself.
The Overdrive is actually two chasses, the DAC itself, and a separate power supply that Steve refers to as the Substation Power Supply. The two are connected by a DC power supply umbilical cable which is included. The chasses are identical in size and overall appearance, and are quite compact, each measuring only 7 inches wide, 7 inches deep by 2.5 inches tall. Their look is a clean industrial design, which I find extremely attractive. The review unit had a silver face, but black is also available.
The back of the Power Station has an IEC socket for an AC power cord, and a balanced socket for the umbilical. The front face has the vertical lights on the extreme right, and in the center is a recessed panel with a toggle switch, which turns on and off power to the DAC itself.
The DAC has a series of heats fins on the top. Around back is a connector for the DC umbilical, as well as the following digital inputs:
- USB 2.0 (for a Mac or PC; supports up to 24/192)
- S/PDIF coax – BNC (RCA adapter included; 44.1, 88.2, 96 and 192 are supported at 16 and 24-bits
- I2S (Empirical standard RJ-45); 44.1, 88.2, 96 and 192 supported at 16 and 24-bits
It will be noted that the Overdrive does not handle DSD, a point I will return to later.
For the review I used a USB cable from my Mac Mini, and an RCA cable from my modified SONY which I use solely as an optical transport.
For the output, there are both RCA and XLR (left and right channels).
On the front face are three colored vertical lights on the extreme right; just to their left is a volume control, and to the left of it is a recessed panel with five toggle switches, two of which are further recessed. The leftmost of the two recessed switches controls overall gain; the upper position is low-gain, which is recommended when the Overdrive is connected directly to an amp. The lower position is high-gain, which is recommended for use when directly driving an amp which itself drives low efficiency speakers, or when connected to a line-level preamp. For the review I used my Miracle Audio Divinitive XR preamp between the Overdrive and my amps, and thus used the high gain position. The rightmost recessed switch selects between volume control (up position) and line out (down position). Because I controlled volume with the Divinitive XR preamp, I used this switch in the down position, thereby bypassing the Overdrive’s volume control.
Regarding the three “main” toggle switches: the rightmost switch selects input (USB, I2S, and S/PDIF); the middle switch selects between low, medium, and high frequency roll-offs (per Steve’s recommendation, I used this in the high frequency position); and the leftmost switch is a de-emphasis switch which reduces harshness on some older recording with pre-emphasis; I did not enable this function.
The design criteria for the Overdrive DAC include the following:
- Low jitter Clocks
- Low jitter 192 Async USB interface module
- Ultra-Simple pure Class-A analog Path
- a single stage to do I/V conversion, analog filtering, gain and output drive.
- D/A Volume Control
- Ultra-Linear Output Stage
- Fully Balanced Analog Path
- A large number of Black-Gate electrolytic capacitors
- Optimized power supply, including extensive use of Hynes regulators
The Company One Keeps
To ensure that I had a good source, Steve included a Mac Mini with Hynes Power supply, running Amarra software (which works with iTunes). The hard drive contained a wealth of terrific music, which I used along with some of my own music for the review. On the last day of the review I inadvertently deleted all of Steve’s Playlists. I already apologized to him, but would like to do so again. Sorry Steve. I will try to be more careful next time.
Toward the end of the review I retuned Steve’s computer to him (minus his playlist; sigh) and used my own Mac Mini, with a brand-spanking new Kaia Power Supply from Ryan Mintz of Core Audio Technologies (http://www.coreaudiotechnology.com/kaia-linear-power-supply), running Amarra. I downloaded the necessary driver from Steve’s website.
As an aside, with my previous PC-based HAL MS-1 computer server running JRiver, I was unable to detect a sonic difference between FLAC and WAV files. However, with my Mac Mini/Kaia Power Supply running Amarra, WAV files were noticeably superior to FLAC. There are too many variables involved for me to be able to explain the discrepancy. However, the difference was sufficient such that with the new setup, I will be switching to WAV.
Amplification was via a Miracle Audio Divinitive XR preamp , feeding Merrill Audio Veritas monoblock amplifiers. Speakers were the Lawrence Audio Double Bass speakers which were in for review, the Sadurni Acoustic Staccato horn speakers (review forthcoming), as well as my Gallo Reference 3.5s. Cabling was entirely from Merrill Audio.
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