Model FP24 User Guide
Microphone Mixer
Headphone Monitoring
General Description
• Switchable between program audio or external (stereo) tape
The Shure FP24 is a studio-quality two-channel, portable, stereo
microphone mixer. With assignable L-C-R inputs, built-in slate mi-
crophone, 1 kHz tone oscillator, and headphone monitor, the FP24
is extremely flexible. Its impressive audio performance and com-
prehensive features make it suitable for the front end of any studio
or field production system. Radio, television, and film production
engineers will especially value its compact size, sunlight-readable
LEDs, and rugged mechanical and electrical construction that
make it able to withstand extremes in the field.
returns.
• High current headphone output has level control and peak
indicator.
Level Metering
• Dual-color LEDs indicate clipping and limiter activity for
each channel.
• Sunlight-readable, seven segment GaN LED output meters.
• 3-position LED brightness switch (intensity selector).
Features
High Performance Microphone Inputs
• Maximum of 66 dB of gain (each input).
Audio Limiters
• “Unclippable” input peak limiters with adjustable limiter
threshold (each input).
• Premium Lundahl input transformers provide superior audio
• Dual mono or linked stereo limiter operation.
quality and freedom from interference problems.
Flexible Powering
• Sealed, conductive plastic potentiometers for long life and
• Internal power from two AA batteries with easy access
reliable gain adjustment.
battery compartment.
• Phantom power, selectable between 48 volts and 15 volts.
• Chassis-isolated 5 to 14 VDC input for easy external DC
• Switchable low-cut filters with 80 and 160 Hz corner
frequencies, 6 dB per octave. Filters are inserted prior to
any active circuitry to maximize headroom.
powering.
• Power LED indicates low battery power.
• Inputs assignable to Left, Center (both left and right) or
Trouble-Free Design
Right
• High-strength, extruded aluminum chassis with protective
metal end panels withstands punishing field conditions.
Audio Performance
• Dynamic range exceeding 110 dB.
• 10 Hz to 50 kHz audio bandwidth.
• Exceptionally low distortion characteristics.
• All-metal connectors mount directly to the chassis for
durability and RF immunity.
• Free from “Pin 1” grounding problems.
• RF filtering on all inputs and outputs.
• Discrete, 6-transistor, balanced output drivers provide signal
integrity over long cable runs.
2005, Shure Incorporated
27A8727 (Rev. 1)
Printed in U.S.A.
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Front Panel Controls, Connectors, and Indicators
1
2
6
9
10
11
L
R
13
4
MIC
+16
0
+4 +8 +12
–30
–15
POWER
FP24
METER
1kHz
12
1
2
L C R
L C R
SLATE
TAPE RTN
PHONES
INT EXT
3
5
7
8
Figure 1. Front Panel
1. Input Gain Controls
8. Tape Return Switch
Sealed, conductive plastic rotary potentiometers.
Toggle switch allows external audio to be monitored in the
headphones. The center position is FP24 program audio.
The left and right positions monitor tape return audio; the left
position is locking, and the right position is momentary.
2. Input Peak/Limiter LEDs
Dual-color LED illuminates red at 3 dB below clipping; illumi-
nates amber to indicate limiter activity.
9. Headphone Connector
3. L-C-R Switches (Input Assignment)
Three-position switch assigns inputs to Left, Center (both
left and right) or Right outputs.
For stereo and mono headphones with ¼” connectors.
10. Headphone Volume Control
4. Slate Microphone
11. Headphone Peak LED
Condenser microphone with AGC activated by momentary
Slate Microphone Switches. Slate Microphone output ap-
pears at all outputs.
Illuminates 3 dB before clipping of either channel of the
headphone circuit and either channel of Tape Return audio.
12. Power Switch
5. Tone Oscillator/Slate Microphone Switch
Toggle switch activates 1 kHz tone oscillator when switched
to the left position and activates the slate microphone when
momentarily moved to the right position. Microphone inputs
are muted when Tone Oscillator or Slate Microphone are
activated.
Three-position switch selects the power source. The unit is
powered from internal batteries when in the left position;
powered from external DC source when in the right position.
Center position is off.
13. Power LED
Two-color LED illuminates green when the unit is powered
and changes to red when batteries require changing. For
external DC, the power LED is always green.
6. Output Meters
Indicates peak output level in dBu.
7. Meter Brightness Control
Three-position switch adjusts the intensity of illumination of
the output meter; low illumination, normal illumination, or
super-bright illumination.
Input Panel Connectors and Controls
3. High Pass Filter Switch
4
Three-position switch selects 80 Hz or 160 Hz corner fre-
quency filters, 6 dB per octave. Filters affect both inputs.
Center position of switch removes filters from the signal
path.
5
TAPE OUT
TAPE RTN
LEVEL
L
R
4. Tape Output
48V
80
LINK
ON
L
R
1
3.5 mm ( / in.) TRS stereo output (unbalanced) can be
8
used to feed consumer level DAT, MiniDisc, and CD record-
ers. Tip = Left, Ring = Right, Sleeve = Ground.
15V
160
THRESHOLD
LIMITER
1
2
7
PHANTOM
MIC INPUTS
5. Tape Return Level Control
Recessed potentiometers adjust Tape Return level feeding
the Headphone Monitor.
1
2
3
6
Figure 2. Side Input Panel
6. Limiter Switch
1. Mic Inputs
Activates input peak limiter. ON position functions as a dual
mono limiter, with each input signal controlling its own limit-
er. LINK functions as a stereo limiter, with both left and right
inputs controlled simultaneously. Center position of switch
turns limiters off.
Transformer-balanced XLR inputs accept microphone level
signals. Pin 2 = hot, Pin 3 = cold, Pin 1 = ground.
NOTE: You can use Shure A15LA line adapters to con-
nect balanced, line-level sources to these inputs.
2. Phantom Power
7. Limiter Threshold Level Control
Three-position switch selects either 48-Volt or 15-Volt phan-
tom power for both inputs. Center position turns phantom
power off.
Recessed potentiometers adjust peak level of limiter activa-
tion. Can be independently controlled for each input.
3
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Output Panel Connectors
1. Strap Slot
Attachment point for camera straps.
2. Tape Return Input Connector
3
2
1
3.5 mm ( / in.) TRS stereo (unbalanced) input for head-
8
phone monitoring of external audio sources.
Tip = left, ring = right, sleeve = ground.
1
4
3. Left and Right Line Level Outputs
Active-balanced XLR line-level outputs. +22 dBu peak out-
put level. Pin 2 = hot, pin 3 = cold, pin 1 = ground. Pin 3
can be grounded or ungrounded to drive unbalanced inputs.
TAPE RTN
5
1(L)
2(R)
4. Battery Compartment
5–14 VDC
LINE OUTPUTS
+
–
Houses two AA batteries. Insert positive (+) end of batteries
first.
Figure 3. Side Output Panel
5. External DC Power Input
Accepts 5–14 VDC from an AC to DC transformer or a bat-
tery supply. Locking, threaded coaxial connector.
Center pin = positive, sleeve = negative. Use the supplied
threaded connector for power supplies with plug-type con-
nectors (such as the Shure PS20). See Figure 5 for wiring
diagram.
Operational Notes
Input Transformers
Phantom Power
The FP24 uses premium Lundahl input transformers with pre-
mium magnetic core material to achieve high signal-handling capa-
bility, flat frequency response and minimum distortion. Because
these transformers provide galvanic isolation from the driving
source, they offer superior isolation from the adverse and uncon-
trolled environments of field-production. Their high common-mode
impedance also provides exceptional common-mode rejection.
Use one of the two phantom power settings on the FP24 for mi-
crophones that require it. Some microphones need the 48-Volt set-
ting to avoid a loss of headroom and increased distortion. The
15-Volt setting, however, lengthens battery life, and electret-con-
denser microphones rated for operation at 15 V or less generally
receive no performance benefit from the 48-Volt setting. Consult
your microphone documentation for phantom power requirements.
Dynamic microphones do not require phantom power. A properly
connected balanced, dynamic microphone is not affected by the
presence of phantom power and does not draw any current. How-
ever, poorly or incorrectly wired microphone cable can cause audi-
ble artifacts in the microphone signal (phantom power can be an
excellent cable tester). It is good practice to turn phantom power off
when not needed.
Output Circuitry and Tape Output
Each line level XLR output of the FP24 uses a discrete, six-tran-
sistor, “impedance balanced” output stage. The circuit uses over-
sized, high speed transistors to achieve low distortion, robust line
driving capability. Pin 2 is driven with signal, and pin 3 is not. (A
common misunderstanding is that a “balanced” output refers to
equal and opposite signals on pins 2 and 3. Correctly, “ impedance
balanced” refers to equal impedances from pins 2 and 3 to ground,
not equal signal voltages.) To drive unbalanced inputs, pin 3 can be
grounded or left unconnected. There is no change in signal level
driving balanced or unbalanced inputs.
High Pass Filter
To remove excess low-frequency energy in the audio signal, use
either of the two high pass (low cut) filter settings on the FP24. Use
the 80 Hz position for most applications, such as recording speech,
music, and ambient sound. The 160 Hz position is useful for en-
hancing speech clarity and reducing wind-noise. The high pass fil-
ter is a single pole design, 6 dB per octave.
The FP24’s tape output feeds consumer-level devices, such as
computer sound cards, DAT or MiniDisc recorders, and cassette
1
1
recorders. A cable wired with 3.5 mm ( / in.) TRS to 3.5 mm ( /
8
8
1
in.) TRS or 3.5 mm ( / in.) TRS to Left/Right phono (RCA) connec-
8
When possible, equalize at the sound source by microphone
selection, placement, use of a windscreen, and onboard micro-
phone filtering. Using both the high pass filter on the FP24 and the
one on a microphone has an additive effect, increasing the overall
slope of the roll-off.
tors will connect the FP24 to such devices.
Using the FP24 as a Mixer
The FP24 can be used as a simple two-channel mixer. Possible
applications include:
Headphone Monitoring and Tape Return
The three position Tape Return switch on the front panel selects
the audio source being monitored:
• Quickly reversing the stereo image of a recording without
reconnecting inputs or outputs.
• During set up, checking for mono compatibility by assigning
Center Position—Program audio (normal operation). Monitors
both inputs to the same output.
the Left and Right outputs of the FP24.
• Recording dialog in mono.
Left and Right Positions—Secondary audio source. Monitors
audio from the Tape Return input of the FP24. Can be used to verify
that signal is reaching cameras and tape machines. Left is locking;
right is momentary.
• Performing “mix minus” by routing Input 1 to Center and
Input 2 to Right. A summed mono signal of both inputs
appears at the Right output while only Input 1 appears at
the Left output. This is useful for post production processing
of Input 1 audio.
Important: The FP24 can drive headphones to very high levels.
Exercise care when monitoring. Reduce the level when the Head-
phone Peak LED illuminates.
4
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Limiters
Power Sources and Battery-Life
The FP24 has two built-in peak-responding limiters, one for each
input channel. Each limiter has a two-stage circuit: the first stage
keeps the input gain stage from clipping; the second stage limits the
variable gain stage according to the Limiter Threshold control set-
ting. This unique, two-stage topology limits the gain stage directly
after the mic input transformer without changing the input imped-
ance as other “at the mic” limiters do. The circuit enables the FP24
to limit in excess of 50 dB, making it very difficult to clip the unit re-
gardless of the gain setting.
The FP24 operates from either two internal AA alkaline cells or
an external 5–14 VDC battery supply or AC to DC transformer
(such as the Shure PS20). The power connector is a locking,
threaded coaxial connector. Center pin = positive, sleeve = nega-
tive. Use the supplied threaded power connector if necessary (see
Figure 5).
The external DC input supply is galvanically isolated (floating)
from the chassis and the rest of the circuitry. The isolation provides
trouble-free interconnection to other pieces of equipment sharing
the same DC power source. The center pin of the locking DC con-
nector is positive, and the sleeve is negative. Since the external DC
supply is floating, the positive or the negative can be connected to
the chassis with no adverse effects.
The FP24’s limiters can operate in either either dual-mono or ste-
reo. Use the three-position switch on the input panel to set the limit-
ing mode:
• In the middle position, the limiters are turned off.
Two AA, 1.5 Volt lithium cells can power the FP24 for up to
approximately 11 hours. However, several factors affect how long
a given pair of batteries will last. These factors include battery
chemistry, ambient temperature, use of phantom power, output
meter brightness, and the output drive level of the FP24. The chart
below provides estimates of battery life in different kinds of circum-
stances. Experimentation can determine expected battery life for
specific setups and environments.
• In dual mono operation (ON switch position), the limiters
work independently, responding only to their input signals.
• In stereo-linked operation (LINK switch position), the
limiters control both channels identically. This maintains a
stable stereo image.
When the limiters activate, the Peak/Limiter LED on the front
panel illuminates amber in proportion to the amount of limiting for
each channel.
NOTE: AA carbon cells and AA nickel-cadmium cells are not rec-
ommended for use in the FP24 since they have lower power capac-
ity than other types and will result in very short service life.
Tone Oscillator and Slate Microphone
The switch labeled 1 kHz/SLATE on the front panel controls two
functions. The 1 kHz position (left) mutes all inputs and sends a 1
kHz sine wave calibration tone at +4 dBu to all outputs. The tone
oscillator can be used to verify connections and set nominal levels
on recording and transmission equipment.
Battery
Type
Microphone Type and
FP24 Settings
Battery
Life
Eveready AA
2 dynamic handheld microphones, low
11 hrs.
6 hrs.
No. L91 (lithium) meter brightness, no headphones
2 dynamic handheld microphones, low
meter, low headphone level
The SLATE position (right) is a momentary switch position that
activates the built-in slate microphone located behind the front pan-
el. When the switch is held to the right, all inputs are muted and
slate mic signal is sent to all outputs. The slate mic circuit contains
an AGC (automatic gain control) to keep the slate level relatively
constant regardless of the acoustic level. Use the slate microphone
to document takes right at the mixer location when microphones
are on talent or away from the production mixer.
2 condenser, 15-Volt phantom pow-
ered microphones, normal meter in-
tensity, normal headphone level
Duracell AA MN
1500 (alkaline)
4 hrs.
2 hrs.
2 studio condenser, 48-Volt phantom
powered microphones, super bright
meter intensity, high headphone level
Test conditions: 70 degrees F, 42 dB of gain with an acoustic music
source, 600 ohm load, +4 dBu output
Metering and Clip-Indicators
Three two-color clip-indicators monitor signal levels throughout
the FP24:
Interconnecting the FP24 and FP33
1. Above each input gain control, a two-color LED glows red 3
dB below clipping. This clip circuit monitors both the front end
gain stage and the variable gain stage.
You can connect the balanced, line level XLR outputs of the
FP24 to the mix bus of the FP33 using the Shure A33LK accessory
kit (or construct a cable assembly as shown in Figure 4 on the fol-
lowing page).
2. A headphone-clip LED, located above the headphone level
control, indicates when either channel of the headphone cir-
cuit approaches clipping.
Combining an FP24 and a Shure FP33 (or FP32A) mixer yields
a flexible, cost-effective, 5 X 2 field mixing setup with the following
features:
3. The headphone-clip LED also indicates when either channel
of the tape return audio is near clipping.
• Simultaneously accepts a stereo microphone, hard-wired
shotgun, and two RF lavalier microphones.
When the limiter is activated, these input LEDs glow amber in
proportion to the amount of limiting.
• 48-volt phantom power for all five microphone inputs
The FP24 has a seven segment LED output meter that shows
peak output level in dBu. From left to right, the first three LEDs are
separated by 15 dB and the remaining LEDs are separated by 4 dB.
This calibration provides a 46 dB-dynamic range with good resolu-
tion in the critical signal level range.
• Limiters on the FP24 inputs
• Input assignment switches on the FP24 and pan pots on the
FP33 inputs
• Two output buses—assignable to mic or line level output.
• Master volume and headphone monitoring for all five inputs
The meter uses premium Gallium Nitride (GaN) LEDs which are
visible even in direct sunlight. A three-position switch on the front
panel controls the brightness of the output meter. Choose low, nor-
mal, or super-bright.
controlled from the FP33.
• Compact—FP24 adds little bulk to an existing FP33
package.
CAUTION – When set to super-bright intensity, the LEDs in the
output meter can irritate or damage eyes with prolonged direct ex-
posure.
• The FP24’s isolated external DC input jack eliminates
ground related interference problems.
5
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This class B digital apparatus complies with Canadian ICES–003.
Eligible to bear CE marking.
NOTE: When interconnecting the FP24 and FP33, inputs from
the FP24 appear at the FP33 mixbus with their polarity reversed.
(This is unavoidable due to the nature of the interconnection.) To
avoid cancellation or interference effects (e.g., comb filtering) be-
tween the signals from the FP24 and FP33 inputs, use Shure
A15PRS polarity inverters on the FP24 inputs, or do one of the fol-
lowing:
Conforms to European EMC directive 89/336/EEC: Professional Audio Products
Standard EN 55103 (1996); Part 1 (emissions) and Part 2 (immunity). The FP24 is
intended for use in environments E1 (residential) and E2 (light industrial) as defined in
European EMC standard EN 55103. It meets the applicable tests and performance
criteria found in the standard for these environments. EMC conformance is based on
the use of shielded interconnecting cables.
N 108
• Keep microphones connected to the FP24 as far away as
possible from those connected to the FP33.
• For microphones that must be close together (such as those
Limited Two-year Warranty
in a stereo pair), connect them to the same mixer.
Shure Incorporated (“Shure”) hereby warrants that this product will be free from de-
fects in materials and workmanship for a period of two years from date of purchase.
At its option Shure will repair or replace the defective product and promptly return it to
you, or refund the purchase price. You should retain proof of purchase to validate the
purchase date and return it with any warranty claim.
NOTE: If constructing your own FP24/FP33 interconnect cable:
• Keep cable length to a minimum, since the interconnection
is unbalanced.
• Be sure to drive the FP33 mix bus off of pin 2 of the FP24
since the FP24 inputs are reverse polarity with respect to
FP33 inputs.
If you believe this product is defective within the warranty period, carefully repack
the unit, insure it, and return it postage prepaid to:
Shure Incorporated
Attention: Service Department
5800 W. Touhy Avenue
FP24 XLR–L
FP24 XLR–R
FP33 mixbus
820 ohm
Evanston, Illinois 60714–4608 U.S.A.
Outside the United States, return the product to your dealer or Authorized Service
Center.
This warranty does not apply in cases of abuse or misuse of the product, use con-
trary to Shure’s instruction, or unauthorized repair. All implied WARRANTIES OF MER-
CHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE are hereby disclaimed
and Shure hereby disclaims liability for incidental, special, or consequential damages
resulting from the use or unavailability of this product.
Some states do not allow limitations on how long an implied warranty lasts, or the
exclusion or limitation of incidental or consequential damages, so the above limitation
may not apply to you. This warranty gives you specific legal rights, and you may have
other rights which vary from state to state.
820 ohm
Figure 4. FP24/FP33 Mix Bus Interconnect Cable
FCC Declaration of Conformity
We of
Positive: Solder to center pin
(marked with a white stripe on PS20 cable)
Shure Incorporated
5800 W. Touhy Avenue
Evanston IL 60714–4608 U.S.A.
847–600–2000
declare under our sole responsibility that the following product,
Model: FP24
Name: FP24 Microphone mixer/preamplifier
was tested and found to comply with Part 15 of the FCC rules.
Negative: Solder to sleeve
Operation is subject to the following two conditions: (1) this device may not cause
harmful interference, and (2) this device must accept any interference received, includ-
ing interference that may cause undesired operation.
Figure 5. Attaching the Supplied Threaded Power
Connector.
Testing was completed by the following NVLAP or A2LA accredited laboratory:
Certification
L.S. Compliance, Inc.
W66 N220 Commerce Court
Cedarburg, Wisconsin 53012
Telephone 262–375–4400
Fax 262–375–4248
Authorized under the DECLARATION OF CONFORMITY provision of FCC part 15
as a Class B digital device. Tested to comply with FCC standards. FOR HOME OR
OFFICE USE. This product complies with part 15 of the FCC rules. Operation is
subject to the following two conditions: (1) this device may not cause harmful
interference, and (2) this device must accept any interference received, including
interference that may cause undesired operation. Changes or modifications not
expressly approved by Shure Incorporated could void your authority to operate this
equipment.
Shure Incorporated, Manufacturer.
This equipment has been tested and found to comply with the limits for a class B
digital device, pursuant to Part 15 of the FCC rules. These limits are designed to
provide reasonable protection against harmful interference in a residential installation.
Signed:
Date: Sept. 15, 2000
This equipment generates, uses and can radiate radio frequency energy and, if not
installed and used in accordance with the instructions, may cause harmful interference
to radio communications. However, there is no guarantee that interference will not
occur in a particular installation. If this equipment does cause harmful interference to
radio or television reception, which can be determined by turning the equipment off and
on, the user is encouraged to try to correct the interference by one or more of the
following measures:
Name, Title: Craig Kozokar, Project Engineer, EMC
S
S
S
S
Reorient or relocate the receiving antenna
Increase the separation between the equipment and the receiver
5800 W. Touhy Avenue, Niles, IL 60714-4608, U.S.A.
In U.S.A., Phone: 1-847-600-2000 Fax: 1-847-600-1212
In Europe, Phone: 49-7131-72140 Fax: 49-7131-721414
In Asia, Phone: 1-852-2893-4290 Fax: 1-852-2893-4055
International Fax: 1-847-600-6446
Connect the equipment into an outlet on a circuit different from that to
which the receiver is connected
Consult the dealer or an experienced radio/TV technician for help
6
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