These days, if one wants to transmit multichannel digital audio data optically, the only store-bought eight-track solution available involves putting one of Apogee’s Fiber DX AMBUS card into one of its AD-8000 boxes. The AMBUS card converts the internal Apogee AMBUS data format to the long optical wavelengths and ST connectors used by Wadia and Apogee.
Product PointsApplications: High-quality remote recording scenarios
Key Features: Converts bidirectionally between plastic optical cable system and glass optical cable system
Contact:Merging Technologies at 847-272-0500; www.merging.com.
+ Well built
+ Uniquely functional
– Each unit acts as both transmitter and receiver – you pay for some features you might not use
The Score: The first standalone multichannel plastic-to-glass converter solution – if you need to run ADAT ODI data anywhere between 6 feet and 3,000 feet, this is the way to do it.
What do you do at the other end? Buy another expensive AD-8000 to act as a receiver? I’ve had a dozen custom boxes built for me – designed simply to go back and forth between ST-glass and ADAT ODI and AES/EBU. Z-Systems also put six ST glass fiber-optic transmitters and receivers in the most recent 16×16 distribution box I bought from the company last summer.
So, sending multichannel ADAT-type digital data over great distances can be done, albeit with a lot of custom work. As far as I’m concerned, the useful upper limit of ADAT-ODI plastic fiber cabling is about three feet, and 18″ sounds even better. I can easily hear the deleterious effects of six feet of plastic fiber.
If you want to really hear how bad the jitter added by longer lengths of plastic fiber-optic cable sounds (to train your ear to hear smaller amounts), just try one of those 13′ or 16′ long lightpipe cables and compare its sound with that of an 18″ cable. You’ll be amazed!
I was overjoyed when I discovered that Merging Technologies built the very converter boxes I had been searching for. The Onouris Long Distance Fiber-Optic Converters are little silvery units measuring about 7 inches by 4 inches by 1 inch. Each front panel has two sets of three optical connectors: one unit’s receiver converts from glass input to two plastic outputs in parallel, while the other one converts from a plastic fiber-optic input to one glass transmitter, wired in parallel with two plastic transmitters (in pass-through/distribution mode).
There is also an alternate optical distribution amp mode that, when selected by an internal jumper change, allows a source fed into the Glass In receiver to be redistributed to the Glass Out and the three Plastic Out connectors. I have configured two of my four Onouris units in this manner, and have labeled them strictly as receivers.
The Onouris units contain no switches and, therefore, no complexities – just a power LED that indicates proper AC operation. There are no wallwarts – the Onouris units accept AC directly; 115 V and 230 V versions are available separately. Two units are included in the Onouris Long-Distance System (OLDS), a solution said to work without problems up to 600 meters. With a small internal resistor change, the system can apparently work even up to 1,000 meters. I have successfully used the Onouris boxes with 150-meter glass cables – the maximum distance I have ever needed to send multichannel digital data.
Standard (ADAT-compatible) TOSlink connectors operate at a nominal wavelength of 660 nanometers. This works fine for low-cost All Plastic Fiber (APF) such as that generally used in the ADAT-compatible lightpipe world, and allows transmission distances of up to a maximum of 10 meters under optimal conditions – your mileage may vary. Actual maximum distance may further be limited to only about 6 meters over plastic fiber, depending on manufacturer’s implementation and choice of optical connectors.
In the case of the Onouris units, Merging Technologies employs mechanically similar Toshiba transmitting and receiving modules, but they are optimized to operate at the longer wavelength of 800 nanometers. This wavelength (in the near infrared) allows transmission distances of up to 1 kilometers with proper 200 micrometers Plastic Clad Silica Fiber (PCSF). (Silica is the generally used terminology in optical fiber to refer to glass fiber since glass is made out of silica.)
It is important to note that this 800-nanometer wavelength, while being optimum (low loss/meter) for PCSF is not at all optimized for standard APF. It is thus not a good idea to use these connectors to terminate transmitters and receivers designed for plastic fiber – the maximum distance over standard plastic cables would be even less than normally achieved with 660-nanometer transmitters. Loss over plastic cables is so great at 800 nanometers that transmission is not reliable after a few (say 4 meters to 5 meters) of plastic fiber.
The Onouris boxes clearly indicate where to connect glass fibers and where to connect plastic fiber. One cannot reliably use the high-class and long Merging Technologies PCSF cables to connect to standard ADAT ODI-compatible transmitters and receivers, however tempting that idea might seem.
My first listening tests were done with standard ADAT ODI-compatible equipment and APF plastic fiber cables to determine the necessity (or not) for the extra conversion complexity afforded by the Onouris units. It was during these trials that I came to my own conclusions (cited above) about the coarsening of sound quality as the plastic APF fiber reached lengths greater than a couple of feet.
While I had heard various opinions about maximum lengths bandied about over the years by audiophile reviewers, this is the first time I did my own listening tests. The 15-foot standard APF cables do work; they just sound terrible!
At any transmission distance greater than 2 feet or 3 feet, inserting a set of Onouris boxes into the signal path improved the sound quality – irrespective of the length of PCSF glass fiber used between them. That is to say, whether one uses 10 meters or 100 meters of glass fiber cable between Onouris units, the sound does not change.
With APF plastic fiber, the sound gets rougher and rougher as one exceeds 1 meter. I’ve been sending stereo data down hundreds of feet of glass fiber cable for years and have been quite happy with the sound quality. The Onouris converter set now extends this quality level to multichannel digital data.
For anyone transmitting high-quality digital data in the ADAT ODI format, I consider Merging Technologies’ little Onouris boxes to be a serious must-buy unless, of course, one is able to keep one’s plastic APF fiber cable lengths extremely short.