Shure FP42 User Manual 3

Model FP42 User Guide

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Stereo Microphone Mixer

GENERAL

The FP42 is a 4-input, 2-output, compact, self-contained stereo
mixer for applications in broadcasting, recording and sound rein­forcement. The high-reliability FP42 integrates all the operating
features of a professional stereo mixer in a single unit—small and
lightweight enough for location use, but with the reliability of a stu­dio console.

FEATURES

S Wide, flat frequency response, low distortion, and high

output level

S Reliable operation under all temperature and humidity

conditions

S Protected against RF interference and damage from input

overload and shorted outputs

S Four transformer-coupled XLR inputs, each microphone-line

switchable with low-cut filters and cuing function

S Full-separation pan pots with center detent on each input for

precise spatial positioning

S Phantom power for condenser microphone operation
S Built-in tone oscillator permits level checking and line testing
S Left- and right-channel transformer-coupled XLR outputs,

with microphone-line and mono-stereo switches

S Parallel stereo headphone jacks (1/4-inch and mini) with

level control

S Left and right mix bus jacks
S Active, feedback-type input gain controls for high-level input

signals without input attenuators

S Adjustable-threshold limiter with left- and right-channel peak

indicators

S VU meters with range switch and battery check function
S Left- and right-channel master level controls and ganged

headphone level control

S Powered by ac (120 or 240V—internally selectable) or

built-in battery pack

S Low battery drain provides up to 10 hours operation under

normal conditions

S Noiseless and automatic switchover to and from battery

power

S Rugged, durable construction
S Compact and lightweight for field use and transporting
S Rack-mountable with accessory rack mount kit
S Listed by Underwriters Laboratories, Inc.;

listed by Canadian Standards Association as Certified

CONTROLS AND CONNECTIONS

Power Off/On Switch: applies power to the FP42 circuitry.

Channel Level/Cue Rotary Controls: adjust individual input

channel signallevels. Each channel can be cued by pulling the con­trol knob outward, rotating the knob to the desired level, and push­ing the knob inward to activate the channel.

Lo Cut Filter Slide Switches: reduce unwanted low-frequency
signals such as wind noise by 6 dB per octave at 150 Hz.

Pan L --R Rotary Controls: assign each input channel signal to the
left (L) or right (R) output channel, or equally to each output channel
(center detent).

Master Rotary Control: determines mixed output level at left (L)
and right (R) output connectors. The control is “clutched”: both
channel levels can be set simultaneously, or the left (inner knob) or
right (outer knob) channel can be set individually. The control also
sets the tone oscillator level when the ToneOsc switch is turned on.

Mono/Stereo Slide Switch: selects either monophonic output sig­nals (both left and right output connectors carry the same signal) or
stereo operation (input channel signals are assigned to left or right
output channels depending on Pan control positions).

Limiter In/Out Slide Switch: activates fast-acting, peak-respond­ing limiter circuit to cut overload distortion during loud program in­tervals without affecting normal program levels.

Peak/Limiter LEDS: indicate limiter operation with the limiter in,
and indicate approaching program overload with the limiter out.
The LEDs are activated by the shortest transient peak, but remain
on long enough to provide easy recognition.

L and R VU Meters: indicate 0 VU with a +4 dBm output (recom­mended for normal use to provide approximately 14 dB headroom
from operating level to clipping level). Rear-panel VU Range +4/+8
slide switch permits changing to 0 VU = +8 dBm. The VU meters are
lit during ac operation only; therefore, the illumination serves as a
visual alarm if the ac is interrupted and the unit has automatically
switched to battery operation.

Batt Check Momentary Push-button Switch: operates in con­junction with the left-channel VU meter to indicate battery condi­tion. With the Power switch on and the switch depressed, a new set
of batteries will give about a +2 VU i ndication. Battery condition is
good if the reading is above 0 VU: a lower reading means that new
batteries are required for proper operation.

T one Osc Off/On Slide Switch: provides a highly stable, low-dis­tortion 1-kilohertz tone for line tests and level checks. The tone sig­nal level is controlled by the Master Level control. The tone signal
appears on both the line and microphone outputs, as well as the
Headphones and Mix Bus connectors. The tone oscillator should
be switched off when not in use.

Headphones 1/4-inch Stereo Phone Jack and Miniature 3.5
mm Stereo Phone Jack: permit monitoring mixer output through

most stereo headphones. The Headphones rotary control adjusts

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the output level of both left and right channels. Note that the head-

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phones output level is high enough for use as an auxiliary unbal­anced line feed to drive a tape deck or a power amplifier.

Input 1–4 XLR Connectors: are balanced, professional, three-pin
audio connectors. Pins 2 and 3 are “hot,” and pin 1 is ground. For
microphone operation, the Input Mic/Line switches must be in the
Mic position; for line level inputs, the switches must be in the Line
position. Phantom Off/On Slide Switch: controls the application of
phantom power for condenser microphones to all inputs. With the
switch on and Input Mic/Line switches in the Mic position, +30 Vdc
is applied to pins 2 and 3 of each input connector. Series current­limiting resistance is 3.3 kilohms for each input. When using other
than Shure condenser microphones, verify that the voltage and re­sistance requirements are compatible.

Output L and R XLR Connectors: are professional, three-pin au­dio connectors for connection to either low-impedance microphone
or line-level inputs of power amplifiers, mixers, or other signal-proc­essing equipment. The Output Mic/Line switch selects either mi­crophone- or line-level output signals.

Mix Bus L and R Phono Pin Jacks: provide direct access to the
left and right output channel mixing buses. This facilitates stacking
or “multing” FP42s to achieve additional input capacity without los­ing any inputs. With two FP42s connected at their mix bus jacks, for
example, the left and right mix buses of each unit are directly con­nected, providing two independent (ganged) master gain controls
and two isolated line amplifiers with eight individually controlled in­puts. Since the buses are directly connected, a 6 db drop in the gain
of each output channel will occur, and the master or input controls
must be increased to compensate.

Adjustments

Turn the Power switch to the On position (VU meters will light in ac
operation). Turn the Phantom switch on if non-battery-operated
condenser microphones are to be used with the FP42. (Caution: Do
not turn the Phantom switch on when using unbalanced low-imped­ance microphones; objectionable hum will result.) Note that phan­tom power cannot be applied to the inputs with the Mic/Line
switches in the Line position; if line-level condenser microphones
(such as Shure’s SM82) are to be operated on phantom power,
contact Shure’s Customer Services Department for modification in­structions.

Turn the Limiter switch to Out. For each input channel, apply an in­put signal and rotate the associated Pan control to assign the signal
to the left or right output channel as desired. Adjust the Channel
Level control for each channel so that the VU meter needles move
with the audio signals in the 0 VU to –20 VU range, with occasional
movement into the 0 VU to +3 VU (red) area. With the limiter out, the
red Peak/Limiter LEDs will flicker as the signal level approaches
clipping.

If desired, activate the Lo Cut Filter switches above the Channel
Level controls. The filter action will help reduce wind noise and un­desirable low-frequency signals such as from condenser micro­phones or turntable rumble (see Figure 1).

INSTALLATION AND OPERATION

Battery Operation

In addition to 120- or 240-volt ac operation, the FP42 can be oper­ated from an internal battery pack. Current drain is typically 32 mA
at + 4 dBm output level. Battery operation is recommended for re­mote, on-location operation, and as an emergency backup source
in case of ac power failure.

Access to the battery compartment is through the bottom of the
chassis. Three 9-volt transistor radio batteries power the FP42 at
full rated output. Use alkaline batteries for maximum life. Battery life
is approximately 10 hours at +4 dBm continuous use. Note that
phantom power loading will increase battery drain.

With batteries in the battery compartment, the FP42 will automati­cally and silently switch to battery operation should the ac voltage
fall below a suitable level.

Battery condition can be determined by using the Batt Check switch
on the front panel. With the FP42 power switch on, activate the Batt
Check switch, and observe the VU meter. A new set of batteries will
give about a +2 VU indication. Battery condition is good if the read­ing is above 0 VU; a lower reading means that new batteries are
required for proper operation. (Note that the FP42 power switch
must be turned on to check battery condition.)

Connections

Connect the signal sources to the three-socket XLR Input connec­tors and set the Mic/Line switches for the proper level. Connect the
three-pin XLR Output L and R connectors to low-impedance micro­phone or line-level inputs of power amplifiers, mixers, VTRs, etc.
Set the Output Mic/Line switch for the appropriate signal level.

If desired, connect additional FP42s or other mixers using the Mix
Bus phono pin jacks. A common ground connection can be estab­lished using the rear-panel Ground binding post.

Connect the line cord to a 120 Vac +10%, 50/60 Hz source if the
FP42 is to be ac-operated. If 240-volt ac operation is desired, refer
to the Service section.

LO-CUT FILTER ACTION

FIGURE 1

Note that each input Channel Level control has a cuing capability.
To cue a channel while the other channels are carrying program
material, pull the desired channel Level control outward to the cue
position. This removes that channel from the mixing circuitry and
routes it only to the Headphones jacks. Adjust the Headphones lev­el control to a comfortable listening level, and adjust the cued chan­nel Level control for a proper mixing level. Restore the cued signal
to the program mix by pushing the Channel Level control inward.

The limiter circuit is activated by the Limiter switch. With the switch
set to In, mixer output is limited to the preset threshold level of +14
dBm. Increasing the Channel Level or Master gain controls in­creases the average output and the amount of limiting. To adjust the
limiter threshold, refer to the Service section.

With the limiter circuit in, the Peak/Limiter LEDs light to show limiter
action. The LEDs respond much faster than VU meters and are ac­tivated by extremely short transient peaks, but remain on long
enough for easy recognition.

VU Meter

The VU meters are factory-calibrated for use with a 600-ohm termi­nated line. The VU Range switch on the rear panel selects either a
+4 or +8 dBm output at 0 VU meter indication. (This switch changes
the meter indication but does not change the actual output level.)
Microphone output levels are 50 dB below line output. The +4 range

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