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REPRINTED
WITH PERMISSION
FROM THE JUNE 1995
ISSUE OF EQ |
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LSI FIBOX FIBER OPTIC
SYSTEM |
| LIGHTWAVE
Systems, Inc. (LSi) licenses some of its technology from Lester Audio Laboratories, one of
the early developers of fiber-optic systems for pro audio. The original work
concentrated on the development of fiber-optic snake systems that would carry large
numbers of audio signals between remote locations. The Lightwave Systems products
concentrate on smaller-scale applications of this technology that can be expanded or
distributed as required to suit different applications. For |
used as a
2-channel mic preamp for recording on one day and on the next day as a distribution system
to serve live sound and broadcaster mixers simultaneously. The |
and no
short circuits. The LSi
Fibox system is a series of 1/3-rack-space-wide interlocking modules (1 U high) that can
be combined in various configurations to |
series: the
FBAI-M, a 20-bit A/D 2-channel fiber-optic interface with mic preamps; and the FBAO-M, a
fiber-optic interface that outputs 2-channel analog audio through a |
 DUELING FIBOXES: The FBAI-M (top) and the FBAO-M. |
 |
20-bit
D/A converter. These two solid little black boxes could easily be used just as a
high-quality mic preamp in anything from location recording to a project studio; the
fiber-optic aspect might simply be a bonus. There are also modules in this series
that provide AES/EBU digital outputs for direct connection to a DAT recorder or digital
workstation, and interface modules for SMPTE timecode signals and other forms of data.
Optional rack-mount ears allow the units to be |
| many
users, this means thay can buy a few Fibox systems and change the configuration each time
they are used. These Lego-like boxes may be |
great
advantage of fiber systems is their ability to provide absolute isolation between inputs
and outputs of the system. No hum, no buzz, |
allow up
to 12 channels of audio to be sent down a single fiber-optic cable. I was supplied
the first two production modules available in this |
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| installed
into a standard rack. The
FBAI-M front panel features two identicalinput sections with a flush-mounted gain control
and mic/line level selector switch. There are also switches for 48 V phantom power
(mic level only) and the power switch. A green LED indicates power and two red LEDs
next to each of the gain controls indicate clipping (OL). The connectors are mounted
on the rear panel: two female-XLRs for audio in; a 15-pin sub-D connector for stacking
audio from up to 12 units onto a single fiber; the ST-type fiber optic connector; and a
coaxial power connector. There is also a polarity switch for reversing pins 2 and 3
on input 1 of the unit.
The FBAO-M front panel simply offers
a |
stereo
headphone jack to quickly verify the presence of signal, a power switch, and the green LED
power indicator. The rear
panel looks similar to the input unit except the XLRs are male, the stacking connector is
a 25-pin sub-D connector, and the switch is for disconnecting the audio ground from the
chassis of the unit. Both units use substantial wall-wart power supplies along with
the nonlatching connector. This format of power supply can be a problem, especially
when securing them in a portable rack. [LSi has revised the wall-wart supply in later
production models to reduce its size and added a latching coaxial power connector.]
An optional rack-mount power supply is available that also includes |
battery
backup for critical applications. The unit functioned flawlessly during my testing, with transparent
transmission of the audio (see fig. 1) and complete freedom from artifacts and noise (the
microphones were noisier than the mic preamps and the rooms were noisier than the best
mics). The gain controls did jump in level in the last 10 degrees of rotation, a
problem common to many mic preamps. The unit does allow accurate level setting and
the recessed controls prevent accidental adjustment. The D/A converter unit runs hot
to the touch, so it should be mounted where sufficient convection cooling is available.
[LSi states that the revised power supply in later models does not suffer from this |
problem.]
The 20-bit A/D and D/A converters allow you to maintain a good safety margin before
clipping without compromising noise. This feature is especially important because
the gain controls will typically be out of reach at the mic preamp and not at the mixing
console or recorder. If
you are plagued by electro-magnetic interference in your audio lines, ground-loop
problems, or are just looking for a good mic preamp, then you should consider the Fibox.
You can buy the fiber-optic cables prebuilt if you don't want to build you own, and
you will quickly learn to appreciate the reduction in cable size and weight. The
phone companies have been using this stuff for about 30 years; now it's our turn. |
 MANUFACTURER:
Lightwave Systems, Inc., 900 Jackson Street, Suite 700, Dallas, TX 75202. Tel:
214-741-5142.
APPLICATIONS: Modular stereo
converters for sending interference-free audio signals over fiber-optic cables up to 2.5
miles in length.
SUMMARY: A high-quality mic
preamp combined with 20-bit A/D and D/A converters to provide ground-isolated optical
transmission of audio signals.
STRENGTHS: Extremely low
noise and distortion, offering the user a cutting-edge technology for the price of a good
mic preamp.
WEAKNESSES: New technology
with connectors you won't find at Radio Shack for a while yet.
PRICE: $749.50 per module;
$1499 per 2-channel system as reviewed.
BY WADE MCGREGOR |
 FIGURE
1: The LSi Fibox system has an extremely flat frequency response (red) and phase response
(blue) throughout the A/D, fiber-optic link, and D/A signal chain. |
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