In order to protect your device and your speakers from
accidental damage, Bias Series amplifiers include an
extensive automatic protection system.
14.1 Turn-On/Turn-Off muting
For about four seconds after turn-on, and immediately at
turn-off, the amplifier outputs are muted. Class D amplifiers
may cause severe speaker damage at power up due to the
high voltage levels at the output stage.
In order to avoid this, the outputs are muted for about 4
seconds after turn on. Similarly, turning off the amplifier can
cause the same problem: outputs are muted immediately at
turn off.
14.2 Short circuit protection
Short circuits or very low impedance loads may destroy the
output stage of any amplifier.
In order to protect the amplifier from the dangerously high
current surges arising from accidental output short circuits
or low impedance loads, all K series amps stop channel
activity when the current drawn from the load rises above
a set threshold.
In case of short circuit, the topmost front panel red LED will
light-up. At the same time, the “PROT” warning appears in
the first line of the LCD display. The channel is muted for
2 seconds after which the amplifier will check whether the
current draw is still over the safety threshold. Should this be
the case, the amplifier maintain muted the channel and the
procedure will reiterate every 2 seconds.
The amplifier will therefore automatically self-reset the chan-
nel every 2 seconds. Once the amplifier channel has under-
gone 50 resets and the output current draw is still above safe
limits, the channel enters a permanent protection mode: an
on/off cycle is needed to restart the unit and restore it to full
functioning mode. The red LED will be turned off and the
amplifier will return to normal operating conditions only when
the output current draw returns to acceptable levels.
14.3 Thermal protection
All Bias Series amplifiers use a continuously variable speed
fan to assist cooling (the fan speed changes in response to
the amplifier’s cooling needs).
If the heat sink temperature reaches approximately 80°C,
the yellow front panel LED starts blinking. If the temperature
should rise above 85°C the thermal sensing circuitry will
mute each power section channels, the yellow LED will be
steadily on, and the power supply will be cut off. At the same
time, the “PROT” warning appears in the first line of the LCD
display.
14 System and signal protections
Once the heatsink has cooled down, the amplifier will auto-
matically reset and the yellow LED will go off. One possible
way to reduce the temperature is to reduce the output power.
14.4 DC fault protection
In order to protect your speakers from mechanical damage
caused by a DC signal coming from the amplifier’s output, a
DC detection circuit is placed between the amplifier’s output
stage and power supply.
If a DC signal or excessive subsonic energy appears at a
channel output an instantaneous protection circuit will cut off
the power supply to both channels. Power supply shutdown is
used instead of speaker relays in order to improve the damp-
ing factor and reliability of K Series amplifiers. At the same
time, the “PROT” warning appears in the first line of the LCD
display.
14.5 Input/Output protection
An ultrasonic network decouples radio frequencies from the
outputs keeping the amplifier stable with reactive loads and
protects the loudspeakers against strong very high frequency
non-musical signals above the audible range.
Bias Series User Guide V1.0
Page 35
