MLA-1 / MLA-10
Installation/Operations Manual
Table of Contents
Introduction 1
MLA-1 vs. MLA-10 Comparison 3
MLA-10 Details 4
MLA-1 Details 6
Special Interest Notes 8
1
MLA-1 / MLA-10
Installation/Operations Manual
INTRODUCTION
This is the preliminary manual covering the installation and operation of the MLA1 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 MLA10 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.
2
MLA-1 / MLA-10
Installation/Operations Manual
MLA-10
• The MLA-10 is designed as a
rack-mountable unit. It occupies a
single height of rack and is less than
4 inches deep.
• The MLA-10 is powered by a
UL-approved wall transformer and
has a front panel power switch and
power indicator.
• This unit has eight front panel
LEDs that indicate MIDI activity on
each of the 4 MIDI inputs and 4 MIDI
outputs.
• On the rear panel are 4 MIDI
input DIN connectors and 4 MIDI
output DIN connectors.
• On the rear panel is a 24-
position wire terminal strip for
connection of the multi-pair long
cable. This is a plug-in type, so that
the unit may be removed without
disconnection of individual wires.
MLA-1
• The MLA-1 is designed as a
surface mountable unit. This may be
inside of a wall box. It measures 6.7"
by 6.2" by .8".
• The MLA-1 is normally
powered remotely from a MLA-10,
but may be ordered from the factory
for wall-transformer power.
• Since this unit is normally
mounted inside a wall box, no LEDs
are included.
• MIDI connection is made via a
24 position terminal strip. Normally,
the installer would mount the MIDI
DIN connectors on a wall plate, and
wire these to the terminal strip.
• The unit has another 24-
position wire terminal strip for
connection of the multi-conductor
long cable.
3
MLA-1 / MLA-10
Installation/Operations Manual
MLA-10
The front panel of the MLA-10 has the Power switch and LED and the MIDI
activity LEDs. These activity LEDs will flicker whenever the associated channel
carries MIDI data.
INPUT OUTPUT
Power
12341234
Activity LEDs
The rear panel of the MLA-10 has the power connector for the wall transformer,
the eight MIDI connectors, and the terminal strip for the multi-pair long run cable.
INPUT OUTPUT
1342
1342
Midi Connectors
24
Long run Multi-pair cable
1
The definition of the pins of the terminal strip are as follows:
Pin Name Pin Name Pin Name
1 MIDI In #1 (-) 9 MIDI Out #1 (-) 17 Ground
2 MIDI In #1 (+) 10 MIDI Out #1 (+) 18 Ground
3 MIDI In #2 (-) 11 MIDI Out #2 (-) 19 Ground
4 MIDI In #2 (+) 12 MIDI Out #2 (+) 20 Ground
5 MIDI In #3 (-) 13 MIDI Out #3 (-) 21 +9 VDC
6 MIDI In #3 (+) 14 MIDI Out #3 (+) 22 +9 VDC
7 MIDI In #4 (-) 15 MIDI Out #4 (-) 23 +9 VDC
8 MIDI In #4 (+) 16 MIDI Out #4 (+) 24 +9 VDC
This means that a MIDI signal put into the MLA-10's MIDI Input #1 will be
converted and transmitted out on pins 1 and 2 as a ± pair. Pins 17 thru 24 are
intended as output power to a MLA-1.
Under no circumstances should pins 21
thru 24 be attached between two MLA-10 units.
Power
9VDC
4
MLA-1 / MLA-10
Installation/Operations Manual
Connections- MLA-10 to MLA-1
When attaching a MLA-10 to a MLA-1, wiring is very simple: Pin 1 on the MLA-10
goes to Pin 1 on the MLA-1 and so forth until pin 24.
If only 10 pair cable is used, skip past pins 19 and 20 on both ends. This
will provide two conductors of ground and two conductors of +9 VDC
power.
Connections- MLA-10 to MLA-10
When attaching two MLA-10's together, it is necessary to swap the In's versus
the Out's of the wiring. The connections will be as follows:
Unit Unit Unit Unit Unit Unit
A pin B pin A pin B pin A pin B pin
1 9 9 1 17 17
2 10 10 2 18 18
3 11 11 3 19 19 (optional)
4 12 12 4 20 20 (optional)
5 13 13 5
6 14 14 6
7 15 15 7
8 16 16 8
Clearly, the inputs and outputs have been swapped on one side. Note that pins
21 thru 24 are not attached at either end.
Failure to attach two MLA-10's as shown above will cause output to fight
output, and damage to both units will probably result.
We strongly recommend that a minimum of 22 AWG twisted pair
cable be used. An example of this would be Belden #9747, which is non-
shielded 12 pair.
5
MLA-1 / MLA-10
Installation/Operations Manual
MLA-1
With the cover removed, this PC board is found:
Pin 24
To
Multi-pair
long cable
J1
Note that pin 1's are closest to P C board edge
J1
This connector will attach to the long multi-twisted-pair cable. For each MIDI
channel used, a cable pair is needed. In addition, at least two pair of wires are
needed for power if the MLA-1 is being powered remotely from a MLA-10. If more
conductors are available, they should also be used for power. This will minimize
the voltage drop thru the cable.
When attaching a MLA-1 to a MLA-10, wiring is very simple: Pin 1 on the MLA-1
goes to Pin 1 on the MLA-10 and so forth until pin 24.
If only 10 pair cable is used, skip past pins 19 and 20 on both ends. This
will provide two conductors of ground and two conductors of +9 VDC
power.
J2
Pin 24
To
Midi DIN
Connectors
Pin 1Pin 1
We strongly recommend that a minimum of 22 AWG twisted pair
cable be used. An example of this would be Belden #9747, which is non-
shielded 12 pair.
6
MLA-1 / MLA-10
Installation/Operations Manual
J1 Connector
Pin Name Pin Name
1 Chan 1 Out (-) 13 Chan 3 In (-)
2 Chan 1 Out (+) 14 Chan 3 In (+)
3 Chan 2 Out (-) 15 Chan 4 In (-)
4 Chan 2 Out (+) 16 Chan 4 In (+)
5 Chan 3 Out (-) 17 Ground
6 Chan 3 Out (+) 18 Ground
7 Chan 4 Out (-) 19 Ground
8 Chan 4 Out (+) 20 Ground
9 Chan 1 In (-) 21 +9 VDC
10 Chan 1 In (+) 22 +9 VDC
11 Chan 2 In (-) 23 +9 VDC
12 Chan 2 In (+) 24 +9 VDC
(Note that some units are silk-screened to have pins 9 thru 16 as channels 5 thru
8. The wiring is the same regardless.)
J2
This connector carries the actual MIDI signals, and must usually be brought to
normal 5 pin DIN connectors. Normally, these would be mounted to a wall plate.
Any type of wire may be used for these connections. The wiring is as follows:
J2 Pin MIDI Connector J2 Pin MIDI Connector
1 MIDI Out 1, pin 4 13 MIDI In 1, pin 4
2 MIDI Out 1, pin 2 14 No Connection
3 MIDI Out 1, pin 5 15 MIDI In 1, pin 5
4 MIDI Out 2, pin 4 16 MIDI In 2, pin 4
5 MIDI Out 2, pin 2 17 No Connection
6 MIDI Out 2, pin 5 18 MIDI In 2, pin 5
7 MIDI Out 3, pin 4 19 MIDI In 3, pin 4
8 MIDI Out 3, pin 2 20 No Connection
9 MIDI Out 3, pin 5 21 MIDI In 3, pin 5
10 MIDI Out 4, pin 4 22 MIDI In 4, pin 4
11 MIDI Out 4, pin 2 23 No Connection
12 MIDI Out 4, pin 5 24 MIDI In 4, pin 5
(Note that some MLA-1 metal work was silk-screened with MIDI Ins designated
as channels 5 thru 8. The wiring is the same regardless.)
7
MLA-1 / MLA-10
5
Installation/Operations Manual
Please note that a 5-pin DIN connector is not numbered with consecutive pin
numbers. Viewed from the rear, the pin-out for the DIN is:
Rear View, DIN Ja
Pin 4
Pin 2
Pin
Special Interest notes:
1. One output may be connected to as many as 4 inputs. For instance, pins
1 &2 of a MLA-10 could be attached to pins 9 &10 of up to 4 other MLA-10's.
opposite of this is not true!! For instance, pins 1 & 2 of multiple units may not
be attached to pins 9 &10 of another. This would result in outputs fighting each
other.
2. While this multiple-slave approach may be used with MLA-1's also, it is not
possible to remotely power multiple MLA-1's from one MLA-10's. If Multiple
MLA-1's are to be used, contact the factory for instructions about modifying the
MLA-1's for local power.
3. When working with an MLA-1, you will be constructing some number of
panels with MIDI Jacks. You should keep in mind that, according to the MIDI
specification, the MIDI Input jacks have no ground connection. Only pins 4 and 5
need be connected, pin 2 is left unconnected. The MIDI Output jacks, however,
have pin 2 going to ground. If you are trying to find a source for 5-pin DIN jacks,
we recommend Switchcraft part number 57GB5F. These can be mounted with
screws or rivets.
The
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