JLCooper MLA-1 - Manual (Page 2)

MLA-1 / MLA-10
Installation/Operations Manual
INTRODUCTION
This is the preliminary manual covering the installation and operation of the MLA-
1 and MLA-10 MIDI Line Amplifiers.
The MLA-1 and MLA-10 are designed to act as long distance "amplifiers" for
MIDI signals. The normal MIDI protocol calls for a maximum cable distance of
about 50 feet, clearly not sufficient for many installations. The reason for this
restriction has to do with the basic type of electrical protocol (current loop), which
lends itself to inexpensive implementation.
Successful installations of 100 feet or so have been made, but require good (low
capacitance) cable. Much more than 100 feet of MIDI transmission requires
some sort of amplification.
The MLA-1 and MLA-10 take a MIDI input and convert it to a "push/pull" signal,
much like RS-422. This low impedance type of signal lends itself to long distance,
high reliability installations required by professional applications.
Since the MIDI signal is converted into a different format, an installation requires
a transmitter on one side of the long run, and a receiver on the other. Both the
MLA-1 and MLA-10 have 4 transmitters and 4 receivers each.
It is important to note that an installation requires either an MLA-1 or MLA-
10 on each side of the long run. Even a single MIDI signal requires this
pairing.
Normally, the long run consists of a multi-conductor cable. A twisted pair is
needed for each MIDI signal. The MLA-10 can provide power to the MLA-1; in
that case an additional number of wires is needed. For instance, a 4 input /
4 output system would need 8 twisted pair (16 conductors) for the signals, and
possibly another 4 conductor for power, for a total of 20 conductors.
The choice between the MLA-1 and MLA-10 depends on mounting and powering
requirements: the MLA-10 is a rack mountable unit with built-in MIDI connectors,
while the MLA-1 is normally meant to be mounted in a wall box where the actual
MIDI connectors are provided on a wall plate. The MLA-1 can receive its power
thru the multi-conductor long cable from a MLA-10 if desired.
As such, the MLA-1 and MLA-10 units are identical in concept, but slightly
different in implementation. We will treat each separately in this manual to
(hopefully) avoid confusion.
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