Owner’s
Manual
UF-2
Universal
Filter
®
A
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*TD-004031-00*
Rev. A
UF-2 UNIVERSAL FILTER
I. DESCRIPTION
The UF-2 is a Mini-Slot accessory dual-channel universal filter for use with QSC amplifiers using the Level
1 or Level 2 Open Input Architecture, such as the EX and MXa Series. Depending on how you set and select
the resistor networks and programming jumpers and switches, you can configure the UF-2 to be a subsonic
or ultrasonic filter, a bandpass filter, or an active crossover.
Using the UF-2 as a crossover is ideal for rental sound systems, since it virtually eliminates the possibility
of unauthorized tampering with crossover settings or incorrect crossover output connections, and the
loudspeaker damage that may result from such user errors.
The UF-2, as does any other Mini-Slot accessory, mounts to an input module (the standard input module,
or any of the Open Input Architecture accessory modules that directly replaces the standard input module)
with a 10-pin header and a 12-pin header that solder to the corresponding holes on the input module. The
installation process involves soldering, so only qualified technical persons should attempt to install the UF2 to the input module; ideally, you should enlist QSC’s Customer Service Department or an authorized
service center to perform the task. The installation section of this manual offers more information about
installing the UF-2.
II. FEATURES
The UF-2 allows independent filtering of the two audio channels. You can select high-pass, low-pass, or
bandpass filtering, as well as the frequencies of the filtering.
Either channel’s circuitry contains electronically balanced input circuitry and bypassable low-pass and highpass circuitry. Each filter circuit has a four-pole (24 dB/octave) Linkwitz-Riley alignment and a “x10” range
switch. Figure 1 shows a block diagram of the UF-2.
Low-Pass Filter Bypass
(+) Input
(-) Input
Input
Differential
Amplifier
Programmable
Linkwitz-Riley
Low-Pass Filter
High-Pass Filter Bypass
1
2
3
Optional
CD Horn
Boost
Programmable
Linkwitz-Riley
High-Pass Filter
3-pin
jumper block
Figure 1—Block diagram of UF-2 (1 of 2 channels shown)
1
1
2
3
Channel
Output
3-pin
jumper block
III. PROGRAMMING THE UF-2
The UF-2 circuit board has four switches, six 3-pin headers, and four SIP resistor network sockets (see
Figure 2). 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 three-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 three-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.
S101
J101
J102
S102
S202
J202
J103
RN102
J201
S201
J203
RN104
RN204
RN202
Figure 2—UF-2 Circuit board switch, jumper and resistor network locations
Notes on Stereo, Bridged, or Parallel Operation
The input board or accessory on which the UF-2 is installed has provisions—switches or headers—for
setting the operating mode of the amplifier, i.e., stereo, parallel-mono, or bridged-mono. In the signal flow,
the Mini-Slot accessory is located somewhere after these switches or headers, so you must configure both
channels of the UF-2 accordingly, regardless of the operating mode selected. Usually you would use
identical settings on both channels in stereo or parallel mode, depending on the application. If the amplifier
is in bridged mode, bypass Ch. 2 of the UF-2 and use the Ch.1 input and processing only.
Bypassing the Filtering
To completely bypass the filtering 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 3). Note: If you neglect to place jumpers
on either header, no signal will pass on that channel.
1
2
3
Pins 1 & 2
shorted together
1
2
3
Pins 2 & 3
shorted together
1
2
3
Figure 3—Jumper positions
Programming the Low-Pass Filter
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. If, however, you do not wish to use the low-pass filter and want to bypass it instead, set the jumper
across pins 1 and 2.
2
To set the corner frequency (at which the output is 6 dB down) of the low-pass filter, choose the appropriate
value and switch setting for RNx02 and Sx01, respectively. (Sx01 is a “x10” range switch. In its upper
position, the frequency range is x10, in the lower it is x1.) Use the table below to select the right combination.
Sx01 = x1
80 Hz
Sx01 = x10
800 Hz
RNx02
120K
100 Hz
120 Hz
1000 Hz
1200 Hz
82K
68K
160 Hz
200 Hz
250 Hz
1600 Hz
2000 Hz
2500 Hz
56K
47K
33K
500 Hz
800 Hz
1600 Hz
5000 Hz
8000 Hz
16000 Hz
18K
12K
5.6K
2000 Hz
20000 Hz
4.7K
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
eight pins are well seated in the socket.
Programming the High-Pass Filter and CD Horn Equalization
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. If, however, you do not wish to use either
one and want to bypass them instead, set the jumper across pins 1 and 2.
To set the corner frequency (at which the output is 6 dB down) of the high-pass filter, choose the appropriate
value and switch setting for RNx04 and Sx02, respectively. (Sx02 is a “x10” range switch. In its upper
position, the frequency range is x10, in the lower it is x1.) Use the table below to select the right combination.
Sx02 = x1
20 Hz
30 Hz
Sx02 = x10
200 Hz
300 Hz
RNx04
120K
82K
40 Hz
50 Hz
80 Hz
100 Hz
120 Hz
150 Hz
200 Hz
400 Hz
500 Hz
800 Hz
400 Hz
500 Hz
800 Hz
1000 Hz
1200 Hz
1500 Hz
2000 Hz
4000 Hz
5000 Hz
8000 Hz
56K
47K
27K
22K
20K
15K
12K
5.6K
4.7K
2.7K
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
eight pins are well seated in the socket.
3
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 UF-2 offers two equalization curves for CD horn correction: one with +6 dB of boost
at 20 kHz (place the jumper across pins 1 and 2 of Jx03), and one with +10 dB of boost at 20 kHz (place
the jumper across pins 2 and 3). If you do not place a jumper in one position or the other, the CD horn
equalization circuit will be inactive.
The table below is a summary of jumper settings for the UF-2.
Pins 1 & 2 Pins 2 & 3
Function
None
Header
Bypass low-pass
J101
Enable low-pass
J101
Bypass high-pass
J102
Channel 1: Enable high-pass
J102
Disable CD horn boost
J103
CD horn boost, +6 dB @ 20 kHz
J103
CD horn boost, +10 dB @ 20 kHz
J103
Bypass low-pass
J201
Enable low-pass
J201
Bypass high-pass
J202
Channel 2: Enable high-pass
J202
Disable CD horn boost
J203
CD horn boost, +6 dB @ 20 kHz
J203
CD horn boost, +10 dB @ 20 kHz
J203
X
X
X
X
X
X
X
X
X
X
X
X
X
X
IV. TYPICAL APPLICATIONS
Subsonic Filter
Subsonic filters are commonly used in sound installations to filter out rumbles and other inaudible or
unwanted low frequency signals and to protect speaker drivers. Vented speaker enclosures in particular
often exhibit a phenomenon in which the acoustical damping on the driver(s) drops at extremely low
frequencies below their own resonant frequency. In a situation like this, a subsonic filter will help to prevent
damage from over-excursion of the speaker cone.
Program settings:
Typ. 20–50 Hz
Subsonic roll-off
Figure 4—UF-2 as a subsonic filter
1. Set the jumper on Jx01 to bypass the low-pass
filter (across pins 1 and 2).
2. Set the jumper on Jx02 to enable the high-pass
filter (across pins 2 and 3).
3. No jumper on Jx03.
4. Insert a resistor network in RNx04 that is appropriate to the desired roll-off frequency—typically 20,
30, 40, or 50 Hz.
4
Ultrasonic Filter
An ultrasonic filter is useful for minimizing RF interference, oscillations, leakage or aliasing from digital
devices, and other signals that are too high in pitch to hear but may wreak havoc in an amplifier system.
Program settings:
Typ. 16–20 kHz
1. Set the jumper on Jx01 to enable the low-pass
filter (across pins 2 and 3).
Ultrasonic roll-off
2. Set the jumper on Jx02 to bypass the high-pass
filter (across pins 1 and 2).
Figure 5—UF-2 as an ultrasonic filter
3. Insert a resistor network in RNx02 that is appropriate to the desired roll-off frequency—typically 16
or 20 kHz.
Bandpass Filter
A bandpass filter may be useful if the speaker system driven by the amplifier has a limited bandwidth.
Minimizing the out-of-the-passband energy may result in reduced distortion and better intelligibility.
Program settings:
1. Set the jumper on Jx01 to enable the low-pass filter (across pins 2 and 3).
2. Set the jumper on Jx02 to enable the high-pass filter (across pins 2 and 3).
3. No jumper on Jx03.
4. Insert a resistor network in RNx04 that corresponds to the lower limit of the desired
frequency passband.
5. Insert a resistor network in RNx02 that corresponds to the upper limit of the desired
frequency passband. This frequency must be higher than the one selected for the
previous step.
CD Horn Equalization Filter
A constant-directivity horn requires a 6 dB per octave high-frequency boost from about 3.5 kHz to provide
a flat frequency response. On the UF2 you must use the CD horn equalization in conjunction with the highpass filter.
Program settings:
1. Set the jumper on Jx01 to bypass the low-pass filter (across pins 1 and 2).
2. Set the jumper on Jx02 to enable the high-pass filter (across pins 2 and 3).
3. Set the jumper on Jx03 to select the EQ curve you desire: across pins 1 and 2 for +6 dB
at 20 kHz, or across pins 2 and 3 for +10 dB at 20 kHz.
4. Insert a resistor network in RNx04 that corresponds to the desired low-frequency roll-off.
5
Subsonic Filter with CD Horn EQ
Use settings 1, 2, and 4 from the Subsonic Filter, and setting 3 from the CD Horn Equalization Filter. This
would be suitable only if the loudspeaker system uses passive crossovers.
CD Horn boost
Subsonic roll-off
Figure 6—UF-2 as a subsonic filter with CD horn EQ
Subsonic and Ultrasonic Filter
Use settings 2, 3, and 4 from the Subsonic Filter along with 2 and 3 from the Ultrasonic filter.
Typ.
20–50 Hz
Typ. 16–
20 kHz
Figure 7—UF-2 as a subsonic and ultrasonic filter
2-Way Active Crossover
This configuration routes the frequencies below a particular frequency to amplifier Channel 1, which shall
drive the low-frequency speakers, and the frequencies above to Channel 2, which shall drive the highfrequency speakers. Using the UF-2 as a crossover requires that you drive both amplifier inputs with the
same full-band signal.
HF Driver
Fc
Channel 2
Amp
Channel 2
Channel 1
Channel 1
SPA-2
LF Driver
Figure 8—UF-2 as a 2-way active crossover
6
Program settings:
1. On the input module, set the amplifier mode to parallel. Alternately, you could use a Ycable to provide the same signal to both channel inputs.
Steps 2 through 5 configure Channel 1.
2. Jumper J101 to enable Channel 1’s low-pass filter (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. If you need subsonic filtering, set a jumper on J102 to enable Channel 1’s high-pass filter
(across pins 2 and 3) and insert a resistor network into RN104 that corresponds to the
roll-off frequency you desire. If you do not want subsonic filtering, set J102 to bypass the
high-pass filter (across pins 1 and 2).
Steps 6 through 9 configure Channel 2.
6. Set J202 to enable Channel 2’s high-pass filter.
7. Insert a resistor network into RN204 that is appropriate to the crossover frequency you
set in #4.
8. 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. If you need ultrasonic filtering, set a jumper on J201 to enable Channel 2’s low-pass filter
(across pins 2 and 3) 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 to bypass the low-pass filter (across pins 1 and 2).
Multi-way Crossover System
The UF-2 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 UF-2. The other basic requirement of using the UF-2 as a crossover
is that you must feed each amplifier with the same full-range signal and use the UF-2 to filter the signals
in the individual channels.
Figure 8 depicts an example of a 4-way system. Because of the multitude of possible system configurations,
the fundamentals of the technique used in the example will be explained below, with a few specifics. The
actual crossover frequencies you should use will depend on your speaker system.
7
Subwoofer
UF-2: Mids & Highs
Ch. 1: LP @ 5 kHz; HP @ 1000 Hz
Ch. 2 LP @ 20 kHz; HP @ 5 kHz
The subwoofer subsystem in the example is driven
by a bridged amplifier. Channel 1 of the UF-2 in this
amplifier is set with the high-pass filter at 20 Hz (for
subsonic filtering) and the low-pass at 150 Hz,
which is the crossover point to the woofers. Channel 2 of the UF-2 is bypassed.
Ch. 2
UF-2
Ch. 1
EX4000
(stereo mode)
Woofer
The woofers are driven by an amplifier operating in
the parallel mode. Both channels of its UF-2 are set
with the high-pass filter at 150 Hz (the crossover
point from the subwoofers) and the low-pass filter at
1 kHz.
UF-2: Woofers
Ch. 1: LP @ 1000 Hz; HP @ 150 Hz
Ch. 2 LP @ 1000 Hz; HP @ 150 Hz
Ch. 2
UF-2
Midrange and High Frequencies
Ch. 1
The remaining speakers are driven by the same
amplifier: the mids by channel 1, and the highs by
channel 2. The settings for channel 1 of the UF-2
are: high-pass at 1 kHz (the crossover from the
woofers) and low-pass at 5 kHz (the crossover
point to the high-frequency drivers).
EX2500
(parallel mode)
UF-2: Subwoofer
Ch. 1: LP @ 150 Hz; HP @ 20 Hz
Ch. 2 Bypassed
Channel 2 of the UF-2 is set for high-pass at 5 kHz.
For ultrasonic protection, the low-pass is set at 20
kHz.
Ch. 2
UF-2
Ch. 1
EX4000
(bridged mode)
Figure 9—Multiple amplifiers with UF-2s,
set up for 4-way crossover operation
V. INSTALLATION
Installing the UF-2 requires PC board soldering skills, so only qualified service technicians should attempt
it. Any authorized QSC service center—or, for an additional installation fee, the QSC factory service
center—can perform the installation.
The UF-2 installs on the amplifier input PC board of any QSC EX Series amplifier. Some older EX amplifiers
may require an upgrade to the current input board. Contact the QSC Service Department for details on
compatibility with older EX amplifiers.
When installed, the UF-2 settings and adjustments are not externally adjustable; this can prevent tampering
by unauthorized users.
Tools and materials you will need:
Soldering iron
Desoldering iron or other suitable desoldering equipment
Phillips screwdriver
Wire cutters
Rosin-core solder
Do not use desoldering braid because it may damage the Mini-Slot socket solder pads on the input board,
and it also might not adequately remove solder.
8
The UF-2 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.
CAUTION: Preparing the input board for installation of the UF-2 involves removing
solder from feed-through holes on a two-sided circuit card. Excessive heat can easily
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
following procedure. Please contact the QSC Customer Service Department if you
feel you might not be qualified to perform the installation yourself. One last warning:
damage caused by an improper installation will void the warranty.
Before you start any work, turn off the amplifier power switch and disconnect the AC power cord from the
AC source. Disconnect all cables from the amplifier’s input panel.
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 10.
LOW IMPEDANCE
CH1
DIR. OUTPUT
Input card
BRIDGE
MONO
CH2
14
18
24
12 10 8
-dB 0
LEVEL
6
4
2
CH2 INPUT CH1
GROUND
STEREO
14
18
12 10 8
24
INPUT
PARALLEL
BRIDGE
-dB 0
CH1
LOW IMPEDANCE
CH2
DIR. OUTPUT
6
4
2
CH1
AUDIO TRANSFORMER
0 70 100 ISOL.OUTPUT
70V 25V
100V
CH2
AUDIO TRANSFORMER
0 70 100 ISOL.OUTPUT
LEVEL
BRIDGE
MONO
70V 25V
100V
Figure 10
Begin the installation by locating and removing the screws securing both the upper blank and lower input
panels to the rear side of the chassis (two screws on each mini panel). See Figure 10. The upper blank panel
will simply drop off when its screws are removed.
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. See Figure 11.
Next, desolder and remove the wire jumper pairs W305/W306 and W405/W406 (W303/W304 and W403/
W404 on MXa Series amplifiers). Under where the jumpers were are two rows of solder pad holes, one with
10 holes and another with 12. These are the Mini-Slot “sockets.” See Figure 11.
Figure 11
9
Continue preparing the PC board by removing solder from all 22 in-line socket holes. Once this is done, you
are ready to install the UF-2.
With the input panel facing you and the component side of the UF-2 board facing away from you, carefully
insert the header pins of the UF-2 fully into the socket holes. Turn the assembly over and solder the UF2 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 UF-2 header pins as required.
Reconnect the ribbon cable to the input board connector. Press the locking clamp wings of the connector
closed. You will feel them snap onto place.
If you need to make any adjustments to the UF-2 settings or if you need to record them, do so now, because
the UF-2 will be inaccessible once the input panel is re-installed into the amplifier chassis.
Carefully reposition the input board/UF-2 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 UF-2 is now complete, and the amplifier is now ready to be re-installed into the system.
VI. WARRANTY AND DISCLAIMERS
Disclaimer
QSC Audio Products, Inc. is not liable for any damage to speakers, amplifiers, or any other equipment that
is caused by negligence or improper installation and/or use of the UF-2.
Product Warranty
QSC Audio Products, Inc. guarantees the UF-2 to be free from defective material and/or workmanship for
a period of three years from date of sale, and will replace defective parts and repair malfunctioning products
under this warranty when the defect occurs under normal installation and use—provided the unit is returned
to our factory via prepaid transportation with proof of purchase (sales receipt). This warranty provides that
examination of the returned product must disclose, in our judgment, a manufacturing defect. This warranty
does not extend to any product which has been subject to misuse, neglect, accident, improper installation,
or where the date code has been removed or defaced.
VII. TECHNICAL ASSISTANCE & SERVICE
Servicing your unit requires a trained technician capable of performing the type of service you need. There
are no user serviceable components inside your unit and the danger of electric shock exists. Additionally,
some of the components in your unit has QSC specific parts that require QSC replacements. Comprehensive service manuals for some models are available at QSC.
Technical Assistance
If you suspect that your UF-2 is defective, check your system configuration and UF-2 settings to determine
the origin of the problem. In many cases, incorrect audio interfacing, poor cabling, or other system level
impairments are the cause of problems in audio systems. For technical assistance beyond the information
given in this manual, QSC Technical Services may be contacted.
10
Factory Service
In the event that your UF-2 does need factory service, you may reach QSC Technical Services for return
instructions. A Return Authorization (RA) number must be obtained from QSC Technical Services. QSC
may not account for products that are returned without a Return Authorization number.
Product Return Guidelines
1. Pack the product well for protection during shipment. QSC will provide the factory
packaging free of charge upon request.
2. Include a copy of the sales receipt, your name, return address, phone number, and
defect description with your return correspondence.
3. Call QSC Technical Services for a Return Authorization number.
4. Mark the Return Authorization number on the outside of the packaging.
5. Ship the product prepaid to QSC Audio Products. We recommend United Parcel Service
(UPS).
QSC Technical Services
1675 MacArthur Blvd
Costa Mesa, CA 92626
Telephone:
(800) 772-2834
(714) 957-7150
(714) 754-6175
Fax:
(714) 754-6173
Bulletin Board: (714) 668-7567
Qualified Service Centers
QSC maintains a service center network for your convenience. If you choose to return your product to a local
service center, you may call QSC Technical Services for a referral. Accessories, input modules and other
peripheral QSC products must be returned to the factory for service.
International Servicing
For QSC products that are purchased outside of the United States, service must be referred to the distributor
or dealer from where the product was purchased. There are numerous service centers in many countries.
The service centers in your country may be located by your dealer, distributor, or by contacting QSC
Technical Services.
®
A
“QSC” is a registered trademark of QSC Audio Products, Inc.
U
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1675 MacArthur
11 Blvd. Costa Mesa, CA 92626
(714) 754-6175 FAX (714) 754-6174