JBL Professional MPC-XU User Manual

I. Description

MPC-XU Universal Crossover

For JBL MPC and MPA amplifiers
Owner’s Manual and Installation Guide

The MPC-XU is a dual-channel universal crossover filter accessory for use with JBL MPC
and MPA power amplifiers.

The MPC-XU is user configurable to fulfill these functions:

 active crossover
 bandpass filter
 subsonic filter
 ultrasonic filter

The MPC-XU allows independent filtering of the two audio channels. The choices are:

 high-pass filtering (selection of 19 frequencies)
 low-pass filtering (selection of 17 frequencies)
 bandpass filtering (selection of any combination of the high-pass or low-pass frequencies)

Figure 1. One channel of the MPC-XU

Each channel has an electronically balanced input and bypassable low-pass and high-pass
sections. Each filter circuit uses a 4-pole (24 dB/oct) Linkwitz-Riley alignment.

An alternative to the MPC-XU, the MPC-X100 is preset at 100 Hz for use only as a
subwoofer crossover.

The MPC-XU installs onto the amplifiers input card, where its settings are not easily acces­sible to the user. This makes the MPC-XU ideal for installed or rental sound systems, since it
practically eliminates the danger of unauthorized tampering with crossover setting or
incorrect crossover output connections, as well as the loudspeaker damage that may result
from such user tampering.

Installing the MPC-XU involves soldering a 10-pin and a 12-pin header into corresponding
holes on the input card, a process that only qualified technical persons should attempt. We
recommend that you enlist an authorized JBL service center to perform the task. See the
installation section of this manual for more information.

Figure 1 shows a block diagram of one channel of the MPC-XU:

Programmable
Linkwitz-Riley
Low-Pass Filter

Programmable
Linkwitz-Riley
High-Pass Filter

*TD-000082-00*

TD-000082-00

Rev. B

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II. Installation

CAUTION: The MPC-XU contains active components which can be damaged by electro­static discharge (ESD). Be sure to practice standard ESD precautions, and always ground
yourself and your workstation before handling exposed circuit cards.

Installing the MPC-XU requires PC board soldering skills. Only qualified service technicians
should attempt it. Any authorized JBL service center can perform the installation.

The MPC-XU installs on the amplifier input board of any JBL MPA or MPC amplifier.

Tools needed:

Soldering iron

¼-inch (6.3 mm) nutdriver

Phillips screwdriver

Wire cutters

Rosin-core solder

Desoldering iron or other suitable desoldering equipment (Do not use desoldering braid; it can

damage the solder pads on the input board and might not remove solder adequately.)

CAUTION: Preparing the input board for installation of the MPC-XU involves removing
solder from feed-through holes on a 2-sided circuit board. Excessive heat can damage the
solder pads you will be working on. Proper equipment and experience with desoldering
delicate PC board circuitry is essential to successfully perform the procedure. Damage caused
by improper installation is not covered under warranty.

Input panel

CH2 CH1

10 10

12

88

66

14

44

18 18

22

24

0

-dB -dB

CH2 INPUT CH1

12

14

GROUND

STEREO

24

0

PARALLEL BRIDGE LEVELLEVEL

INPUT

Figure 2a. The input panel’s location
on the rear panel of the amp

1 Turn off the amplifier and disconnect the AC power cord from the AC source. Disconnect

all cables from the amplifiers input panel.

2 Position the amplifier so the rear of the chassis is facing you. The input panel is located on

the left side of the rear panel. See Figure 2a.

LOW IMPEDANCE

AUDIO TRANSFORMER

CH1

CH1

070100

DIR. OUTPUT

ISOL.OUTPUT

70V

25V

BRIDGE

100V

MONO

LOW IMPEDANCE

AUDIO TRANSFORMER

CH2

CH2

070100

DIR. OUTPUT

ISOL.OUTPUT

70V

25V

BRIDGE

100V

MONO

Figure 2b. The input panel (MPC)

Wire jumpers: W303/304 and
W403/404 (MPC); or W305/
306 and W405/W406 (MPA)

Solder holes for MPC-XU

Figure 2c. The input panel (MPA)

3 Locate and remove the screws securing both the upper blank and the lower input panels to

the rear side of the chassis (2 screws on each mini panel). The upper blank panel will
simply drop off when its screws are removed.

4 Gently pull the lower input panel out from the amplifier. Once it is removed, you will

notice a ribbon cable connecting the input PC board to the amplifier. Disengage the
locking wing clamps on the ribbon header and carefully remove the ribbon head from the
socket on the board. Now the input panel assembly is completely free from the amplifier.

5 Desolder and remove the wire jumper pairs indicated in Figure 2b or 2c.

6 Under where the jumpers were located, youll find two rows of solder pad holesone

with 10 holes and another with 12 holes. Remove the solder from all 22 holes.

7 With the input panel facing you and the component side of the MPC-XU board facing

away from you, carefully insert the header pins of the MPC-XU fully into the socket holes.
Turn the assembly over and solder the MPC-XU in place. Make sure all the header pins are
well soldered. Visually inspect for cold solder joints and verify that you have sufficient
clearance to re-install the ribbon connector on the top side of the assembly. Finish by
trimming the MPC-XU header pins as required.

2

NOISE SHIELD

#4-40 NUT

CH. 1 GAIN CONTROL

NOISE SHIELD

INPUT PANEL PCB

TAB

Figure 3 Figure 4

8 If you need to make any adjustments to the MPC-XU settings or if you need to record

them, do so now, because the MPC-XU will be inaccessible once the noise shield is
installed and the input panel is re-installed into the amplifier chassis. See Section III,
Programming the MPC-XU, below.

9 Using a ¼-inch (6.3 mm) nutdriver, remove the outer 4-40 nut from the stud in the panel

mounting bracket, next to Channel 1s gain control potentiometer. Place the noise shield
over the circuit board of the MPC-XU (Figure 3) and bend the grounding tab down so its
hole goes over the stud. Re-install the nut, and tighten it securely (Figure 4).

10 Reconnect the ribbon cable to the input board connector. Press the locking clamp wings

of the connector closed. You will feel them snap into place.

11 Carefully reposition the input board/MPC-XU assembly into the amplifier chassis and

secure it by fastening the two mounting screws. Make sure the screws are tightened snugly,
but do not over-torque them. Re-install the upper blank panel.

Installation of the MPC-XU is now complete, and the amplifier is now ready to be installed
into the system.

III. Programming the MPC-XU

The MPC-XU board has four switches, six 3-pin headers, and four SIP resistor network
sockets (see Figure 3). All these are used for programming the module. The circuitry for the

Figure 5. The MPC-XU’s switches, jumpers, and resistor networks.

Setting input operating mode on amplifier or input card

The input board or accessory on which the MPC-XU is installed has provisionsswitches or
headersfor setting the operating mode of the amplifier. In the signal flow, the MPC-XU is
located after these switches or headers, so its operation is affected by the mode setting.

Stereo or Parallel Mode OperationIf the amplifier is to be used in stereo or parallel
modes, configure both channels of the MPC-XU accordingly.

two channels is identical, so the switches, headers and sockets
are divided between them: those designated by a 3-digit
number starting in a 1 (switches S101 and S102, headers J101,
J102 and J103; and SIP resistor network sockets RN102 and
RN104) are for Channel 1, while those with a 3-digit number
starting in a 2 are for Channel 2. The following instructions
will use an x in place of the first digit, except where a specific
channel reference is necessary.

Bridged Mode OperationIf the amplifier is to be used in bridged mono mode, bypass
Channel 2 of the MPC-XU and use only Channel 1s input and processing.

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