MPC-XU Universal Crossover
For JBL MPC and MPA amplifiers
Owner’s Manual and Installation Guide
I. Description
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)
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 acces-
sible 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
Figure 1. One channel of the MPC-XU
*TD-000082-00*
TD-000082-00
Rev. B
1
NOISE SHIELD
#4-40 NUT
NOISE SHIELD
TAB
CH. 1 GAIN CONTROL
INPUT PANEL PCB
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
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.
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.
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.
3
Bypassing the filters
To completely bypass the filter circuitry of a channel, set the jumpers on both Jx01 and Jx02
across pins 1 and 2, which are the upper two pins on their headers (see Figure 6). Note: If you
neglect to place jumpers on either header, no signal will pass on that channel.
Figure 6
Programming the low-pass filter
Switch Sx01 in
"×1" position
Switch Sx01 in
"×10" position
Resistor network
in RNx02
Bypass/enable header—To use the low-pass filter, set the jumper on
Jx01 across pins 2 and 3, which are the lower two pins on their header.
But if you do not wish to use the low-pass filter and want to bypass it
instead, set the jumper across pins 1 and 2.
80 Hz
100 Hz
120 Hz
160 Hz
200 Hz
250 Hz
500 Hz
800 Hz
1600 Hz
2000 Hz
800 Hz
1000 Hz
1200 Hz
1600 Hz
2000 Hz
2500 Hz
5000 Hz
8000 Hz
16000 Hz
20000 Hz
120K
82K
68K
56K
47K
33K
18K
12K
5.6K
4.7K
Setting frequency—To set the corner frequency (at which the output
is 6 dB down) of the low-pass filter section, choose the appropriate
resistor network value and switch setting for RNx02 and Sx01, respec-
tively. (Sx01 is a ×10 range switch. In its upper position, the frequency
range is ×10; in the lower it is ×1.) Use the low-pass table to select the
right combination. See the appendix of this manual for keys to
identifying the correct resistor network.
Inserting the resistor network—If there is a resistor network already
installed in the socket, carefully pull it straight out. Insert the pins of
the new resistor network into the socket holes and carefully press the
network into the socket. Be careful to avoid bending the pins of the
resistor network. Orientation of the resistor network is unimportant, as
long as all 8 pins are well seated in the socket.
Low-pass filter frequency table
Programming the high-pass filter
Switch Sx02 in
"×1" position
Switch Sx02 in
"×10" position
Resistor network
in RNx04
Bypass/enable header—To use either the high-pass filter or the
constant-directivity horn equalization, or both, set the jumper on Jx02
across pins 2 and 3, which are the lower two pins on their header. But
if you do not wish to use either one of these functions and want to
bypass them, then set the jumper across pins 1 and 2.
20 Hz
30 Hz
200 Hz
120K
82K
56K
47K
27K
22K
20K
15K
12K
5.6K
4.7K
"2.7K
300 Hz
40 Hz
400 Hz
50 Hz
500 Hz
Setting frequency—To set the corner frequency (at which the output
is 6 dB down) of the high-pass filter section, choose the appropriate
resistor network value and switch setting the RNx04 and Sx02,
respectively. (Sx02 is a ×10 range switch. In its upper position, the
frequency range is x10, in the lower it is ×1.) Use the high-pass table to
select the right combination. See the appendix of this manual for keys
to identifying the correct resistor network.
80 Hz
800 Hz
100 Hz
120 Hz
150 Hz
200 Hz
400 Hz
500 Hz
800 Hz
1000 Hz
1200 Hz
1500 Hz
2000 Hz
4000 Hz
5000 Hz
8000 Hz
Inserting the resistor network—If there is a resistor network already
installed in the socket, carefully pull it straight out. Insert the pins of
the new resistor network into the socket holes and carefully press the
network into the socket. Be careful to avoid bending the pins of the
resistor network. Orientation of the resistor network is unimportant, as
long as all 8 pins are well seated in the socket.
High-pass filter frequency table
4
CD Horn Equalization (Boost)—In addition to enabling the high-pass filter at Jx02, if you
opt for CD horn equalization you must place a jumper at Jx03 as well. The MPC-XU offers
two equalization curves for CD horn correction:
• For +6 dB of boost at 20 kHz, place the jumper across pins 1 and 2 of Jx03.
• For +10 dB of boost at 20 kHz, place the jumper across pins 2 and 3 of Jx03.
• To bypass the CD Horn Equalization, do not place a jumper in one position or the other.
Pins 1 & 2 Pins 2 & 3
None
The table at left is a summary of the jumper
settings for the MPC-XU.
Function
Bypass low-pass
Header
J101
J101
J102
J102
J103
J103
J103
J201
J201
J202
J202
J203
J203
J203
X
X
X
X
Enable low-pass
Bypass high-pass
Channel 1: Enable high-pass
Disable CD horn boost
X
CD horn boost, +6 dB @ 20 kHz
X
X
X
X
X
X
CD horn boost, +10 dB @ 20 kHz
Bypass low-pass
Enable low-pass
Bypass high-pass
Channel 2: Enable high-pass
Disable CD horn boost
X
CD horn boost, +6 dB @ 20 kHz
CD horn boost, +10 dB @ 20 kHz
X
X
IV. Typical configurations
Subsonic Filter (Infrasonic Filter)
Applications: Subsonic filters are commonly used in sound installations to filter out rumbles
and other inaudible or unwanted low frequency signals and to protect speaker tuned vented
speakers from damage due to excessive energy below the tuning frequency.
For a subsonic filter, determine the lowest useable frequency that the speaker can safely
handle and set the high-pass filter to that frequency. Typical subsonic filters are set at 50 Hz, 40
Hz, 30 Hz or 20 Hz.
Program settings:
1 Set Jx01 to bypass the low-pass filter (if not using) by placing jumper across pins 1 and 2.
2 Set Jx02 to enable the high-pass filter by placing jumper across pins 2 and 3.
3 No jumper on Jx03.
4 Insert proper resistor network in RNx04 socket.
5
Ultrasonic Filter
Applications: An ultrasonic filter is useful for minimizing RF interference, oscillations,
leakage or aliasing from digital devices, or other signals that are too high in pitch to hear but
may wreak havoc in an amplifier system.
Typical ultrasonic filters are set at 16 kHz or 20 kHz.
Program settings:
1 Set Jx01 to enable the low-pass filter by placing jumper across pins 2 and 3.
2 Set Jx02 to disable the high-pass filter (if not using) by placing jumper across pins 1 and 2.
3 No jumper on Jx03.
4 Insert proper resistor network in RNx02 socket.
Bandpass Filter
Applications: A bandpass filter is useful if the speaker system has a limited bandwidth.
High-pass
freq. (set
Low-pass
freq. (set
by RNx04
and Sx02)
by RNx02
and Sx01)
Program settings:
1 Set Jx01 to enable the low-pass filter by placing jumper across pins 2 and 3.
2 Set Jx02 to enable the high-pass filter by placing jumper across pins 2 and 3.
3 No jumper on Jx03.
4 Insert proper resistor network corresponding to the lower limit of the desired passband in
RNx04 socket.
5 Insert proper resistor network corresponding to the upper limit of the desired passband in
RNx02 socket.
CD Horn Equalization Filter
Applications: A constant directivity horn requires a 6 dB per octave boost at high frequen-
cies to provide a flat frequency response. On the MPC-XU you must use the CD horn
equalization in conjunction with the high-pass filter.
Program settings:
1 Set Jx01 to bypass the low-pass filter (if not using) by placing jumper across pins 1 and 2.
2 Set Jx02 to enable the high-pass filter by placing jumper across pins 2 and 3.
3 Set Jx03 to select the EQ curve you desire: across pins 1 and 2 to +6 dB at 20 kHz, or
across pins 2 and 3 for +10 dB at 20 kHz.
Subsonic Filter with CD Horn EQ
Applications: This would be suitable only if the loudspeaker system uses a passive crossover.
Program settings: Use settings 1, 2 and 4 from the subsonic filter instructions and setting 3
from the CD horn equalization filter instructions above.
Subsonic and Ultrasonic Filter
Program settings: Use settings 2, 3 and 4 from the subsonic filter instructions along with 2
and 3 from the ultrasonic filter instructions above.
6
MPC-XU
2-Way Active Crossover
This configuration routes the frequencies below a particular frequency to amplifier Channel 1,
which will driver the low-frequency speaker(s), and the frequencies above to Channel 2, which
will drive the high-frequency speaker(s). Using the MPC-XU as a crossover requires that you
drive both amplifier inputs with the same full-band signal.
Program settings:
1 On the input module, set the amplifer mode to parallel. Alternately, you could use a Y-
cable to provide the same signal to both channel inputs.
Channel 1:
2 Set J101 to enable the Channel 1’s low-pass filter by placing jumper across pins 2 and 3.
3 No jumper on J103.
4 Insert a resistor network into RN102 that is appropriate to the desired crossover frequency.
5 Subsonic (infrasonic) filter—If you need subsonic (infrasonic) filtering, set J102 to enable
the high-pass filter by placing jumper across pins 2 and 3, and insert a resistor network into
RN104 corresponding to the roll-off frequency you desire. If you do not want subsonic
(infrasonic) filtering, set J102 to disable the high-pass filter by placing jumper across pins 1
and 2.
Channel 2:
6 Set J202 to enable the Channel 2’s high-pass filter by placing jumper across pins 2 and 3.
7 Insert a resistor network into RN204 that is appropriate to the desired crossover frequency.
8 CD horn EQ—If you need equalization for a constant-directivity horn, set a jumper on
J203 for the amount of boost you need. If you do not want CD horn equalization, do not
place any jumper on J203.
9 Ultrasonic filtering—If you need ultrasonic filtering, set a jumper on J201 across pins 2 and 3
to enable Channel 2’s Low-pass filter and insert a resistor network into RN202 that
corresponds to the desired roll-off frequency. If you do not want any ultrasonic filtering,
set the jumper on J201 across pins 1 and 2 to bypass the low-pass filter.
Multi-way Crossover System
The MPC-XU allows you to set up 3- and even 4-way systems. Of course, this also requires that
you use more than one amplifier and more than one MPC-XU. You must feed each amplifier
with the same full-range signal and use the MPC-XU to filter the signals in the individual channels.
Each MPC-XU should be configured in the bandpass filter configuration as described above.
7
V. Warranty & Contacting JBL
These products are designed and backed by JBL Professional, the world leader in sound
reinforcement. For complete JBL warranty information, to order replacement parts or to ask
for clarifications to this manual, contact JBL Professional:
Within the United States: Contact the Applications Dept, JBL Professional, PO Box 2200, 8500
Balboa Blvd, Northridge CA 91329 USA. In the USA you may call Monday through Friday
8:00 a.m. to 5:00 p.m. Pacific Coast Time: (818) 894-8850.
In other areas throughout the world: Contact the JBL Professional Distributor in you country.
A list of JBL Professional Distributors and U.S. Service Centers can be attained from the JBL
Appendix
Identifying resistor networks
Use this chart to identify the values of the resistor networks. See the tables on page 4 to find
the correct values for the desired filter frequencies.
RESISTANCE CODE
2.7K 272
3.9K 392
4.7K 472
5.6K 562
6.8K 682
8.2K 822
10K 103
12K 123
15K 153
18K 183
20K 203
22K 223
27K 273
33K 333
39K 393
47K 473
56K 563
68K 683
Use only these three digits to
determine resistance code.
Disregard the other
numerals and letters.
JBL Professional 8500 Balboa Boulevard, P.O. Box 2200 Northridge, California 91329 U.S.A.
A Harman International Company
MPC-XU MANUAL 3/99
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