Operation Manual

FP+ Series Operation Manual 14
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 frequen-
cies, and may be damaged as a consequence.
Use a high-quality stranded loudspeaker
cable, and keep cable runs as short as
possible.
5.4.5 Output bridge mode
It is possible to bridge channels in two-channel ver-
sions, or in pairs of two (A+B and C+D) in four-channel
versions. When bridged, the input source must be
connected to input A (A+B) or C (C+D) respectively.
Output speaker cables must be connected to the
plus pole on channel A or C and the minus pole on
B or D.
The main benet of bridging the output is a doubling
of output voltage. Bridging can be used to turn a
four-channel FP 10000Q amplier, for example into
a three-channel amplier with 2 x 1300 W and 1 x
4200 W at 8 ohms or 2 x 2100 W and 1 x 5000 W
at 4 ohms
Most power amplier designs, when bridged, auto-
matically introduce a +6 dB input gain boost which
can lead the user to conclude that said amplier
delivers “more than double the power” when in
bridge mode. This is clearly not the case, as the
gain boost articially enhances perceived power at
the cost of headroom. The FP+ Series ampliers
work on globally set constant gain, and automatically
compensate the input gain by -6 dB. For example, if
the amplier is congured in a three-channel mode,
then the selected gain is maintained from input to
output on all channels.
5.4.6 Amplier Gain
All FP+ Series ampliers feature adjustable input gain.
This versatility enables the amplier to accommodate
a multitude of system congurations with various
input sources and speaker layouts. Amplier gain is
set globally for all channels. The range is +23 dB to
+44 dB in 3 dB steps. Individual channel ne level
adjustment is available using the potentiometers on
the front panel.
The unique adjustable input gain feature of the
FP+ 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 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 amplier
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.
5.4.6.1 Channel gain/level (front-panel pots)
Individual channel gain (level) may be adjusted using
the potentiometers located on the front panel. Range
is from 0 dB to -innity in 31 steps. The attenuation
is logarithmic, with the 12 o’clock position indicating
-10 dB.
If the level control is used to attenuate to a
lower level than the headroom relative to
input sensitivity AND the amplier input is
driven into clip, there is a danger of clipping
the input stage before the current or voltage peak
limiters are activated.
5.4.6.2 Amplier sensitivity
Sensitivity is dened 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 FP+ Series ampliers
are capable of providing multiple maximum output
power levels through use of the VPL feature, many
sensitivity calculations may be required for a single
amplier. 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).
OPERATION AND PERFORMANCE 5