ART DI/O: Tu be, or not Tu be…
Frank Alles
6 July 2001


Sample Rate: Switchable 44.1/48/88.24/96kHz - 128x oversampling
Inputs and Outputs: S/PDIF and ¼" Stereo Analog
Tube Designation: Hand-selected, Dual Triode 12AX7 Tube
Channels: 2 Channels of A/D and D/A Conversion
Sync: intelligent Sync ñ Covers a Wide External Range
External Sync Range: 22kHz to 100 kHz
Digital Interface: S/PDIF Coaxial, In and Out, RCA Jacks
Frequency Response: 10Hz to 30 kHz, +/- 0.5 dB
Dynamic Range: 100dB typical
Maximum Input Gain: +20dB
Maximum Input Level: +20 dBu
Maximum Output Level: +20 dB.
Input Impedance: 100K Ohms
Output Impedance: 220 Ohms
Power Requirements: USA - 9vac @ .8A (typical). Export Units are configured for country of destination
Price: $249

Applied Research and Technology
215 Tremont Street
Rochester, NY 14608
Voice: 716.436.2720
Fax: 716.436.3942

Recently, I conducted an A/B test of a neat and inexpensive digital processor, the ART DI/O (digital input/output) against the Perpetual Technologies P-3A processor with the ModWright Signature modifications.

The DI/O, manufactured by Applied Research and Technology (ART), is one of those unique products that one normally discovers entirely by accident, or hears about from one’s audio buddies, who proceed to make claims that any right-thinking audiophile would scoff at. My personal inducement to try the DI/O came from Stereo Times’ publisher, Clement Perry, with some additional impetus from fellow ST writer Marshall Nack. In a phone conversation with Nack, I was told that the diminutive $249-wonder was quite the adroit performer, comparing favorably to his beloved $5,000 reference DAC. So, I just had to try one for myself.

ART, a New York-based firm, is a manufacturer of electronics for musical instruments and professional recording applications, so the DI/O was not actually designed for use in the consumer audio market. Looking over the DI/O’s various inputs, outputs, and other features, that fact is readily apparent. Not only does the unit provide digital to analog conversion, it provides analog to digital, to boot. This facilitates the recording of musical instruments and other analog sources directly to a digital recording medium, including a pc’s hard drive. In addition the unit provides D to A conversion—the process normally employed in the audio-playback chain.

A Crystal Semiconductors CS8427 digital transceiver is used in conjunction with a AK-4524 codec, by Asahi Kasei Microsystems (AKM), to convert analog to digital, and/or digital to analog. [Note: codec is a device that converts, or encodes, analog signals into a form for transmission on a digital circuit. The digital signal is then decoded back to analog at the receiving end of the transmission link. The acronym is from enCOde/DECode.]

The DI/O’s analog inputs and outputs are provided via standard ¼" phono plugs, the type normally found on guitar amplifiers, and, as DI/O owners have found, you need to buy phono plug-to-RCA jack adaptors to facilitate the use of standard interconnects with RCA plugs. One digital input and one digital output are provided on S/PDIF coaxial RCA-type connectors. The DI/O does not upsample, but the input sampling rate is switchable between 44.1, 48, 88.2, and 96 kHz, with 128x oversampling. There is a front panel potentiometer that adjusts the level of the incoming analog signal and another pot to dial in the user’s preference for "Tube Warmth," from transparent to warm.

There has been much ado among audiophiles regarding the "Tube Warmth" feature. The controversy centers on whether the unit’s single 12AX7 tube is in the D to A loop, or the A to D loop. The owners manual states that the tube is in the A to D circuit and is used for sweetening digital recordings—it is not used in audio playback. A phone call to ART’s Sr. Engineer, Mitch Milton, has verified that this is in fact the case. As further ironclad proof, Mitch suggested that I remove the tube from the unit and then play it. Omitting the tube is actually a good idea because not only will the DI/O run much cooler, but it will require less current from the power supply. I’m running my DI/O sans tube and guess what—it sounds exactly the same as it did with the tube!

When I removed the cover from my DI/O, I found it very cramped in there. I think the tube was actually touching the flanking electrolytic capacitors. Sheesh! My original intent was to remove the tube, and also to find a way to install quality RCA connectors for the analog outputs. However, I became discouraged from adding the RCAs due to the serious lack of working space.

To address another topic, for those audiophiles who find that the reversal of absolute polarity is audible, the DI/O lacks any provision for switching absolute polarity.

Rationale/System Configuration

In order to match the volume levels of the two converters for my evaluation, I had to use a passive volume control and an extra pair of interconnects in line with the DI/O’s output. This may have put the DI/O at a slight disadvantage, but was necessary because the output level of the DI/O is extremely high (around 7 volts), and it actually overloaded my preamp inputs when run directly in without attenuation. (Active preamps with electronic volume control are the most susceptible.) Plus, matching the DI/O’s output level to that of the P-3A allowed instant A/B comparisons.

After the ModWright modifications to my P-3A, I find that I prefer the sound of the P-3A used by itself, without the P-1A. So, I connected the P-1A, with its jitter reduction, Resolution Enhancement, and upsampling, to the DI/O in an attempt to even the playing field as much as possible. I also used the DI/O with the stock power supply from the P-3A because it puts out double the current of the smaller wall-wart supply that comes with the DI/O. The P-3A and P-1A were both powered by the Monolithic P3 power supply.

The outputs of the two DACs were then run into the InnerSound preamp (see my full review), with the P-3A on the CD input and the DI/O on the Video input—which have identical performance characteristics.

Playing through various tracks on different CDs, and switching back and forth from my listening seat via the remote, I must state for the record that I was amazed at my inability to detect a difference in any sonic parameter between the two DACs.

To confirm that I wasn't crazy, I asked my wife, Tina, to sit in the listening seat while I performed the same experiment with her. I noticed that she was listening with her eyes closed, which was perfect. After playing through a recording that she chose, Tina opened her eyes and asked me when I was going to make the switch. She was quite surprised to learn that I had switched back and forth at least a dozen times during the cut. I then played music from a few more CDs and still Tina could hear no difference. As for me, whether I listened with my eyes open or closed, I could discern no difference between the two units. This held true for all types of music—vocals, violin, piano, and some very raucous percussion.

The next day, I decided to optimize the DI/O’s performance a bit more by removing the P-3A DAC entirely and connecting the DI/O to the Monolithic P3 power supply. I also tried a different digital cable.

The DI/O seemed to respond quite well to these refinements, producing some of the most captivating and musical sound I have ever heard in my system from a digital source. Playing "I’ll Never Fall in Love Again," performed by Burt Bacharach and Elvis Costello on the Austin Powers: The Spy Who Shagged Me soundtrack CD, I was amazed at how lifelike and natural the cut sounded. I mean, Elvis was literally "there" and the instrumental accompaniment couldn’t have been much more convincing. The depth and control of the lowest bass was very respectable.

From subsequent non-A/B listening sessions, my impression is that the sound of the DI/O (with the P-1A) is quite close to the modified P-3A, especially in the midrange and high frequencies. If there is a difference worth mentioning, it may be in the area of bass performance. In the low- and mid-bass, the P-3A seems to exhibit slightly more control than the DI/O, though this distinction is rather subtle. The DI/O’s bass may be just perceptibly "rounder-sounding" with some material, but it is definitely ample and highly satisfactory.


At this point, I was sold on the charms of the DI/O, but as fate would have it, the unit developed an annoying habit of losing its digital lock when set to the external source (green LED) its best-sounding mode (in my experience and according to the manufacturer). Upon losing the lock it produced an annoying swishing/pulsating noise through the speakers that made me want to reduce the volume. After consulting ART, I returned the DI/O for inspection and possible warranty service or replacement.

ART’s service technician said that he was unsuccessful in getting my DI/O to duplicate the malfunction on the test bench, which I found curious in view of my experience. Be that as it may, they were good sports and sent me an entirely new unit—just in case.

After receiving the new DI/O and installing it in my system, I noticed that there was still a problem getting the DI/O to maintain its digital lock. As it happened, after switching to a different digital cable, the problem abated and the DI/O has maintained its lock ever since. Previously, however, the DI/O lost its lock with more than one of my cables, which now leads me to suspect that the quality of the digital cable and connection are more critical than with other DACs. For example, both the P-1A and the P-3A never failed to lock solidly with the same cables that caused the problem in the DI/O.


Adding the P-1A to the DI/O appears to offer results similar to those attained by using the ModWright P-3A alone, which, in reality, is a little less expensive than the P-1A-DI/O combination. Still, for those who already own a P-1A, or can take advantage of its digital speaker or room correction features, pairing it with the ART DI/O represents a lower-cost alternative to other converters. And for those who require an inexpensive, high-performance DAC that can handle 24/96, the DI/O is an obvious contender.

Top 3 reasons not to buy a DI/O

  1. High >7V output will overload some active preamps

  2. Critical of digital cable/connection

  3. Tube all glow—no show.

Top 3 reasons to buy a DI/O

  1. Low price

  2. Musical & detailed performance

  3. Only $249

The DI/O is generally sold at musical instrument stores such as Sam Ash, and ART has listed its authorized retail outlets on its website. I purchased my original DI/O from for use in a second reference system.