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Contractor Series Power Amplifiers
Reference Manual
Crosstalk, 20 Hz to 20 kHz:
Better than 50 dB below
rated power.
Common Mode Rejection (CMR):
Better than 70 dB
from 20 Hz to 1 kHz.
DC Output Offset (Shorted Input):
±10 mV.
Controls
Level:
A detented rotary level control for each chan-
nel located on the rear panel.
Power:
An on/off rocker switch located on the front
panel.
Mode:
A two-position switch located on the back
panel which, when turned to “Stereo,” operates the
amplifier as two independent channels. When
“Bridge” is selected, the amplifier bridges the two
output channels for twice the output voltage.
Channel Operation Switch (CH Series only):
A two-
position switch located on the back panel which,
when turned to 4/8 Ohm, sets the amplifier to drive
low-impedance speaker loads. Turning the switch to
70V/100V (70V only on the CH4) sets the amplifier to
drive distributed high-impedance speaker loads and
inserts a 70-Hz high-pass filter into the signal chain to
prevent step-down transformer saturation (see Section
4.4).
Indicators
Signal:
A green indicator for each channel which
flashes when a very low-level signal (>-40 dBm) is
present at input. May be used for troubleshooting
cable runs.
Clip:
A red indicator for each channel which turns on
when distortion becomes audible in the amplifier
output.
Fault:
A red indicator for each channel which indi-
cates amplifier has muted output. Normally off. Status
may be monitored remotely by plugging into back-
panel RJ11 Fault jack.
Power:
A blue indicator that turns on when the
amplifier has been turned on and has power.
Input/Output
Input Connector (standard module):
One Neutrik
Combo connector for each channel which features a
balanced
¼
-inch (6.35-mm) phone jack and a 3-pin
female XLR connector, in parallel with a barrier strip
termination.
Input Stage:
Input is electronically balanced and
employs precision 1% resistors.
Input Impedance:
Nominally 20 k ohms, balanced.
Nominally 10 k ohms, unbalanced.
Input Sensitivity:
Channel independent. Factory set
at 1.4 volts for standard 1-kHz, 8-ohm power. 26-dB
gain and 0.775-volt sensitivity available as a Service
Option.
Output Impedance:
See Figures 7.7 and 7.8.
Output Connectors,
CH1 and CH2:
Four-terminal touch-proof barrier
block, one per channel, allows connection of load to
8-ohm, 4-ohm, 70V or 100V outputs.
CH4:
Four-terminal touch-proof barrier block.
CL Series:
Four-terminal touch-proof barrier block.
Output Signal,
Stereo:
Unbalanced, two-channel.
Bridge-Mono:
Balanced, single-channel. Channel 1
controls are active; Channel 2 should be turned down.
Protection
CH and CL Series amplifiers are protected against
shorted, open or mismatched loads; overloaded
power supplies; excessive temperature, chain
destruction phenomena, input overload damage and
high-frequency blowups. They also protect loud-
speakers from input/output DC, large or dangerous
DC offsets and turn-on/turn-off transients.
Options
Service Options: SST-SBSC: variable Linkwitz-Riley
stereo crossover with mono-summed sub-bass
outputs; SST-MX: 100-Hz Linkwitz-Riley crossover with
stereo sub-bass output; SST-SX: 80-/120-Hz switch-
able Linkwitz-Riley crossover with mono summed
sub-bass output.
Construction
Rugged steel chassis is formed into a durable
package, then coated with environmentally friendly
powder for long life and ease of maintenance.
Cooling:
Proportional speed fan.
Dimensions,
Width (all models):
EIA Standard 19-inch rack mount
(EIA RS-310-B);
Height (all models):
5.25-inch (13.34-cm);
