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C Series C 20:8X, C 10:8X, C 10:4X and C 5:4X Operation Manual
at the cost of headroom. The C Series amplifiers
work on globally set constant gain, and automatically
compensate the input gain by -6 dB. For example, if
the amplifier is configured in a three channel mode,
then the selected gain is maintained from input to
output on all channels.
7.4.4 Amplifier input Gain
All C Series amplifiers feature adjustable input gain.
This versatility enables the amplifier to accommodate
a multitude of system configurations with various
input sources and speaker layouts.
Amplifier gain is set globally for all channels on four-
channel models, and in four-channel groups (A-D and
E-H) on eight-channel models. The range is 29-38
dB in 3 dB increments. Individual channel fine level
adjustment is available using the potentiometers on
the front panel.
The unique adjustable input gain feature of the C
Series makes it easier to attain the optimum balance
between headroom and signal-to-noise ratio in the
signal path. A weak signal at the input might require
the gain to be raised in order to achieve maximum
output power with the lowest signal-to-noise ratio. A
“hot” input signal, however, would require a lowering
of the gain to avoid sending the amplifier into Voltage
or Current clipping.
See Appendix to review the table containing Gain
versus VPL setting implications for input sensitivity
and output power.
Bridge mode operation automatically
compensates by -6 dB, keeping all channels
at the same gain.
7.4.4.1 Channel gain/Level (front-panel pots)
Individual channel gain (level) may be adjusted using
the potentiometers located on the front-panel behind
the dust filter cover. Range is from 0 dB to -Infinity
in 21 steps. The attenuation is logarithmic, with the
12 o’clock position indicating -10 dB.
Use your fingers or a screwdriver to adjust the
potentiometers.
If the level control is used to attenuate to a
lower level than the headroom relative to
input sensitivity AND the amplifier input is
driven into clip, there is a danger of clipping the input
stage before the current or voltage peak limiters are
activated.
7.4.4.2 Amplifier sensitivity
Sensitivity is defined as how many volts (rms) or
dBu (referred to 0.775 Vrms) are required to achieve
full (maximum) output power. As the output power
varies with the load impedance, 4 ohms is usually
the common reference.
Since C Series amplifiers are capable of providing
multiple maximum output power levels through use
of the VPL feature, many sensitivity calculations may
be required for a single amplifier. We recommend
use of the DeviceControl software to simplify this
process. DeviceControl’s device view page, used in
combination with the DIP-switch settings display,
will automatically produce a sensitivity calculation
from the given data (VPL, Gain and load).
7.4.5 Output Voltage Peak Limiter (VPL)
The Voltage Peak Limiter (VPL) is a unique feature in
C Series amplifiers. It is used to select the maximum
power available on each output channel. Four levels
can be set using the DIP-switches on the amplifier’s
rear panel.
Figure 9: VPL values in both V peak and Vrms
The values for VPL are displayed as maximum Voltage
Peak. To translate Voltage Peak into Vrms, you must
divide the Voltage Peak values by 1.41 (see table).
The VPL allows you to set the correct maximum
output peak power for optimum performance with
the connected speakers. The correct setting depends
on the system type (low or high impedance) and
the specific load connected to the channel. Since
each channel can be configured to deliver either
very high voltage peak power OR high current draw
at low impedances, it is important to set the VPL
correctly.
V peak
Vrms
100
70.7
63
44.5
45
31.8
32
22.6
7 OPERATION AND PERFORMANCE