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- Never connect an output terminal to ground, or to
any other input or output. Observe relative
loudspeaker polarity: loudspeakers connected in
reverse polarity will exhibit degraded performance,
particularly in bass frequencies, and may be
damaged as a consequence.
- Use a high quality stranded loudspeaker cable, and
keep cable runs as short as possible.
7.4.4 Output bridge mode
When bridged, the input source must be connected
to input A (A+B) or C (C+D) respectively. Output
SpeakON cables must be connected to the bridge
on channel 1+/2+ of channel 1 and 3+/4+ of
channel 4.
The main benefit of bridging the output is a doubling
of output voltage. Bridging can be used to turn a
four-channel by 10K4 amplifier, for example into a
three-channel amplifier with 2 x 1300W and 1 x
4200W at 8 ohms or 2 x 2100W and 1 x 5000W at
4 ohms
Most power amplifier designs, when bridged,
automatically introduce a +6 dB input gain boost
which can lead the user to conclude that said
amplifier delivers more than double the power when
in bridge mode. This is clearly not the case, as the
gain boost artificially enhances perceived power at
the cost of headroom. The 10K4 amplifiers work on
globally set constant gain, and automatically
compensate the input gain by -6dB. 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.
7.4.5 Amplifier gain
The amplifiers of 10K4 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.
The range is +23dB to +44dB in 3dB steps.
Individual channel fine level adjustment is available
using the potentiometers on the front panel.
The unique adjustable input gain feature of the
10K4 amp li fie r 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 maxi- mum 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 -6dB, keeping all channels at the
same gain.
7.4.5.1 Channel gain level (front panel pots)
Individual channel gain (level) may be adjusted using
the potentiometers located on the front panel.
Range is from 0dB to infinity. The attenuation is
-10dB.
- 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.
7.4.5.2 Amplifier sensitivity
Sensitivity is defined as how many Volts (rms) or dBu
(referred to 0.775V rms) 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 the 10K4 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.
Zenith 10K4 Amplifier Manual
19
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