ADAT Extender
ADAT Extender
The ADAT extender can be used to extend 8 channel ADAT data 100 metres or
more using standard CAT5/CAT5e cable.
Combined with suitable analogue to digital and digital to analogue converters such
as the Focusright Octopre or the Behringer ADA8000 you can send up to 8
channels of audio both ways along a single cable. The system also supports word
sync to sample lock the A to D converter to the sample clock of your mixer.
Extending the ADAT signal requires two identical units, one at each end of the
cable.
Each unit has an ADAT optical input and an optical output. When the units are
connected by a CAT5 crossover cable the signal connected to the ADAT input on
one unit appears at the ADAT output on the other unit.
Typical uses include using the system as a digital ‘snake’ for stage or recording
purposes, or as an active mic splitter for simultaneous PA use and recording.
Use of the extender with a digital mixing desk
The ADAT extender can also be used to transmit TOSlink compatible SPDIF data,
in which case the range is considerably extended.
Cable
When two units are connected together, the units are identical, rather than being
dedicated to transmit or receive. Consequently the interconnect cable required is a
standard CAT5/CAT5e crossover cable of the type used to network two computers
without an intermediate hub. The unit has been tested on lengths of standard CAT5
cable up to 100 metres in length. In practice the maximum length of cable may be
far greater and this will depend on the quality of the cable used, but no guarantee
can be given for lengths greater than 100 metres.
Correct wiring for a CAT5 crossover cable
The units will not work with ‘straight’
CAT5 cable, however no harm will
come to the units by use of the wrong
cable provided that it is wired for
CAT5. Alternatively straight CAT5
cables can be used with a crossover
adapter such as Maplin item number
A07AB.
The data sent down the cable is not
ethernet compatible, and it should
never be connected to an ethernet
switch or hub. Connecting it to a hub
will not only prevent the extender
working but could cause damage to
either the unit or the hub.
Beware CAT6! CAT6 cable appears very similar to CAT5, but beware, CAT6
crossover cables are wired differently to CAT5, and can damage the unit. Take care
if buying a commercial crossover cable as many are wired for CAT6. If, when the
units are connected together, the power supply does not power both units, disconnect immediately and check your cable.
Tip: Check the ends of your cable and ensure that the blue wire is in the centre of
the connector at both ends.
Power
The units have their own power regulation and can be powered by any voltage
from 6 to 12 volts. Power is fed via a standard 2.1mm coaxial power connector.
Note the polarity: the centre pin is negative. Accidentally reversing the power will
do no harm as the unit is diode protected.
The CAT5 cable also carries power, therefore when two units are linked, it is only
necessary to use a single power supply. When power is applied to one unit, both
units are powered. If two power supplies are used, each will power it’s own unit
without affecting the other. In some circumstances, depending on cable type, using
two power supplies may improve the distance over which the units will operate.
As the units take very little current, if you prefer, they can be powered for several
hours from a PP3/MN1604 9volt battery.
Warning: If using an unregulated supply, ensure that the supply’s open circuit output does not exceed 18 volts.
Loop mode
Loop mode is turned on by the LOOP switch between the ADAT input and the
ADAT output. When loop mode is turned on, the data on the ADAT input is fed
straight back to the ADAT output as well as being sent down the CAT5 cable.
This feature is useful when the ADAT signal is required in two places. For example, if the ADAT extender is connected to a Behringer ADA8000, selecting loop
mode means that the microphone inputs on the Behringer unit are also fed to it’s
line level outputs. By this method the combination of the mic amp and the ADAT
extender can be used as an active mic splitter.
Obviously, when switched to loop mode, the unit is not capable of receiving a
signal from the other end of the cable.
Word sync
In many cases it is essential that the mic amplifier and A to D converter is synchronised to the sample rate clock of the mixer receiving the output. In all cases
locking digital devices together is recommended, and word clock is a more accurate synchronisation signal than the return ADAT stream.
The word sync channel supports standard TTL level square wave word clock, and
is a totally separate channel to the ADAT audio channels, There is no need for the
signals to necessarily be synchronous.
To use the word sync channel, simply input the word clock into the BNC connecter
on one unit, and set the adjacent switch to TX. With the switch on the other unit set
to RX, the word sync signal is then fed to the output BNC connector on both units.
When the word sync function is not in use, I recommend that both units are set to
RX.
In theory the word sync channel could be used to send other TTL level data
between the units, subject to bandwidth limitations. It is not however suitable for
video or for bipolar data streams such as RS232 or MIDI.
Warning: beware earth currents. In some venues, there may be a significant difference in the earth potential at either end of the cable. This is obviously no
problem with the ADAT signals as they are connected optically.
As the word sync input is an electrical connection, there is a possibility of earth
currents running through the CAT5 cable. To prevent this, the word sync input is
isolated from the unit ground, however it is not possible to isolate the word sync
output, therefore if using the word sync output at both ends of the cable, be aware
that earth currents can occur.
If an earth current is flowing in the CAT5 cable, it can create jitter in the word
clock. More importantly however, severe earth currents caused by an electrical
fault can damage the unit or the cable.
For reasons of jitter, I also recommend that when using the word sync facility, the
unit receiving word clock should be the one which is connected to power.
Using three or more units
By making up a suitable CAT5 parallel strip, more than two units can be used to
make a simple audio network.
Here is an example of a suitably wired parallel strip:
In this case the parallel strip includes the crossover so straight CAT5 cables would
be used.
With this network, the two master units will receive ADAT data from each other,
whereas the two slave units receive data only from Master 1. This may be useful,
for example, to send mic feeds to both a main and a foldback mixer whilst simultaneously sending the mix output to the main PA amplifiers on stage.
Note that adding additional units in this way will reduce the length of cable which
can be used.
Technical Specifications
Power
Input voltage
Absolute maximum rating
Input current
6-12 volts DC
18 volts
approx 70mA per unit
Data
Data format
ADAT Data rate
Maximum data rate1
Maximum sample rate
ADAT digital audio or TOSlink SPDIF
up to 12.3 Megabits/second
15 Megabits/second
8 channels at 48 KHz (as per ADAT spec.)
4 channels at 96 KHz
Transmission distance of optical interface
approx 5 metres on plastic fibre
CAT5 format
Low Voltage Differential Signalling
Signal level
approx 350mV peak to peak
Signal impedance
100 ohms.
Latency1
approx 70nS plus 5nS per metre CAT5 cable.
Transmission distance on CAT5
better than 100 metres2
Data jitter1
better than 16nS on 100 metres of cable
Word clock
Output level
Input impedance
Output impedance
Output rise/fall time
Additional clock jitter1
R.O.H.S. Compliance
approx 3.3 volts peak-to-peak
approx 250 Kohm
approx 95 ohms
approx 250 nS (into high impedance input)
approx 6 ns on 100 metres of cable.
(less than 0.03%)
All components are R.O.H.S. compliant and
unit is manufactured with lead-free solder.
1
Theoretical values, based on manufacturers specifications of component parts.
2
Actual maximum operating distance will depend on cable quality and jitter tolerance of equipment receiving the ADAT output. For standard CAT5 cable and
equipment tolerant of 20% jitter, the system should theoretically work to 150
metres.
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