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Setting Up and Using the Servo 120a Power Amplifier
Bridge switch
Output connectors
Input connectors
Protection LED
Headphone jack and
Speaker on/off switch
Channel Input control
Ten-segment LED meters
Setting up your Servo 120a is a simple procedure which takes only a few minutes:
1. Remove all packing materials (save them in case of need for future service) and decide
where the amplifier is to be physically placed—it can be used free-standing or mounted in a
standard 19" rack, requiring only one rack space. When installed, make sure that there is good
ventilation around the entire unit (we recommend using spacer panels, especially if multiple
amplifiers are used in a rack. Before rack-mounting, use a Philips screwdriver to remove the
Servo 120a’s feet.
2. Set the rear panel Bridge switch as desired (see page 10 in this manual).
3. Make the speaker connections, using the 5-way binding post output connectors on the rear
panel. It is never a good idea to power up any amplifier that is not connected to loudspeak-
ers. In normal operation, any loudspeakers with a minimum impedance load of 4 ohms (that
is, 4 ohms or greater) can be used; however, in Bridge mode, 8 ohm speakers
must
be used.
Be sure to connect the loudspeaker correctly. In normal mode, connect them with the red (+)
terminal connected to the positive input of the speaker and the black (ground) terminal con-
nected to the negative input of the speaker. See page 10 in this manual for connection instruc-
tions when using the Servo 120a in Bridge mode.
4. Next, make the signal input connections, using the electronically balanced 1/4" and/or the
unbalanced RCA-type input connectors on the rear panel (if operating the Servo 120a in Bridge
mode, use the left input only—see page 7 in this manual). If your mixer or crossover network
has balanced outputs, use the Servo 120a’s electronically balanced inputs (unbalanced two-
conductor plugs can also be inserted into these inputs, but you’ll get better signal quality and
less outside noise and hum if you use balanced lines).
5. On the front panel of the Servo 120a, turn both Channel input controls fully counterclock-
wise. Then connect the supplied 3-pin “IEC” cable to the rear panel IEC connector and to any
grounded AC socket. Because of the relay protection circuitry built into the Servo 120a, you
can even plug it into the same power strip that other audio devices (such as a mixing console)
are connected to. You can then turn on all devices at once with the single power strip on-off
switch, with no danger of damaging connected speakers by generating “thumps.”
6. Press the front panel Speaker on/off switch (so that it is in, in its “down” position) and then
press the front panel Power switch in order to turn on the Servo 120a. The Power LED will light
and the Protection LED will go on. After approximately five seconds, the Protection LED will
go off and the Speaker LED (in the Speaker on/off switch) will light instead (you’ll hear a click
when this occurs).
7. Apply an input signal to the Servo 120a at or about +4 dBu (if sending signal from a mixer,
drive the output meters at approximately 0 vu). While the input signal is present, slowly raise
the Channel Input controls until the desired sound level is achieved. The ten-segment LED
meters next to each Channel input control will show you the continuous power output of the
Servo 120a as signal is being passed. For the best signal-to-noise ratio, the Servo 120a should
normally be run with the Channel Input controls at or near maximum and the right-most (+4
dB / 100%) segment should light occasionally (but not frequently) during peak levels. If you
are using a mixer that has a master output level control (sometimes called “Control Room
level”), use it to attenuate the signal as necessary to achieve the desired speaker level.
8. You can monitor the output signal in privacy by connecting a pair of headphones to the
front panel headphone jack and pressing the Speaker on/off switch so that it is out (in its “up”
position), at which time the Speaker LED will go off.
WARNING: Because the Servo 120a is capable of generating extremely high headphone
signal levels, always start with the Channel Input knobs turned down and then slowly
raise them to the desired level.
If you encounter difficulty with any aspect of setting up or using your Servo 120a, you can call
Samson Technical Support (1-800-372-6766) between 9 AM and 5 PM EST.
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