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MP 24x CONNECTION
Even though the system variations are limitless in most
applications where the MP 24x is used, an installer must
follow some basic interconnect guidelines. Unfortunately,
even though the system and the primary components such as
mixers, processors and amplifiers are of commercial grade,
most of the source components, i.e. turntables, disc players,
tape decks and so on are consumer grade, with consumer
interconnect limitations. Therefore, on the input side of the
MP 24x, RCA connectors will prevail with unbalanced lines
thereto attached. It is recommended, for no scientific reason,
that the turntable furthest to the left be connected to Phono 1,
and proceed from left to right with Phono 2 and then Phono 3,
if used. See Service Information on page Schematic-1 to
convert any PHONO level Input into a LINE level Input.
When determining which Line Inputs to use for what, the
process becomes a bit more difficult. Obviously, if one of the
line devices feeding the MP 24x is of the commercial variety
sporting balanced outputs, use Line 2 for this due to its
unique ability to accept such foreign substances. The rest of
the assignments are pretty much a matter of what you want to
appear where on the source switches. As you can see, Lines 1
through 3 appear only on Input Channels 1 and 2; Lines 4
through 6 appear only on Input Channels 3 and 4. So the
layout will depend on how heavily you will use the Phono
Inputs and how many line level devices you will be using.
On the Output side, things are a bit less restrictive. On the
MAIN OUTPUTS you have been given a choice between
XLR balanced and ¼" unbalanced. Which you use should be
derived from some consideration of how far the cable has to
run from the mixer to the next component, how much ambient
noise there is in the local atmosphere (Radio Moscow in the
next building, 36,000 SCR controlled light dimmers in the
next rack), and any other possible encumbrance on the quality
of the audio inside the jacket. Most experienced installers and
users of commercial sound equipment have a good handle on
which to use in a given situation. The general rule is: if the
Output from the MP 24x is running longer than 10 feet, use
balanced cables. If the input to your system equalizer,
crossover, or power amplifier is balanced, go balanced. If
you keep the cable length short and your destination has
unbalanced inputs, you can probably get away with using the
¼" unbalanced connectors.
The TAPE OUTPUTS are unbalanced RCA connectors;
the assumption being that most readily available tape record-
ing equipment such as would be used in a club situation
would be of similar type. Simply determine whether you want
the signal processing in the Effects Loops to have an effect on
the recording being made and connect the record inputs (left
and right) to the appropriate PRE-LOOP or POST-LOOP
TAPE OUTPUTS. These Tape Outputs do not contain any
signal from the Microphone section. If you need to record the
Mic, use the Unbalanced Main Outputs, Zone Output, or the
Manual-6
Booth Output with the Booth Ducker circuit defeated. (If
none of these are available, see Service Information on page
Schematic-1 for internal jumper changing instructions.)
The front panel switchable LOOP is for stereo devices
only, so consider which effects are connected where. Some
processors, such as delays and reverbs, have only one mono
input and two outputs. This is accommodated automatically
by using the MONO Output of the MAIN EFFECTS LOOP.
The Zone Outputs and the Booth Outputs are the auto-
matic mono/stereo type. If mono is required, simply connect
only to the LEFT OUTPUT. Inserting a plug into the RIGHT
OUTPUT automatically renders it stereo. All of these Output
connectors are unbalanced. Attempting to run TRS balanced
on any of these results in an open leg on the receiving
component and causes problems.
This is a good place to discuss the problems encountered
in connecting the MP 24x to all of the different types of
cables and connectors that one finds when basing a system on
consumer goods (the pieces of equipment with the RCA
connectors), commercial audio products (¼", XLR etc.), and
no telling what else. In consumer audio devices, one rarely
finds ground-lift capabilities, or any of the other hum preven-
tion devices normally provided on commercial equipment.
Chassis ground and signal ground are normally the same
thing, a situation which may cause problems when the two
species get on the same bus.
The best we can do to try to help you eliminate hum,
oscillations, or other stray characters from your system is to
tell you to experiment. If you think lifting the ground on the
MP 24x, crossovers, equalizers or power amplifiers might
help, go ahead and try it. There is science involved in de-
humming a system, however it is sometimes faster to just
experiment. Occasionally, directly grounding the chassis of
the mixer to the power amplifiers with a large gauge wire
helps. And by the same token, isolating the two when they are
installed in the same rack may have a quieting effect. A word
of caution: Don't do anything with Level controls up, power
on, or under any condition that could cause damage to
delicate loudspeakers and ears. Make your changes with the
system off, then power up carefully to make sure you haven't
made matters worse. Bring up Level controls slowly and with
great caution. Surprises are nice on birthdays and Christmas,
and rarely any other time.
If hum problems only exist on the Phono Inputs, there is
always a possibility for experimental troubleshooting at this
end also. Experience has shown that just because the manu-
facturers put ground wires on them, they are not always
connected! Some turntables even have two ground wires, one
for the tone arm and one for the chassis. Sometimes only one
of these should be connected for optimum signal-to-noise,
sometimes both, sometimes none. The rule is: "Whatever
works, works."
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