5
OPERATING CONTROLS
The operating controls are located on the front panel except for the AC mains switch.
AC mains switch
The
AC mains switch (9)
is located on the rear panel and connects the 909 from the AC
supply when it is switched to ON.
When it is set to OFF the unit is completely disconnected and the LEDs on the front panel
remains dark.
Switching to ON activates the stand by mode and the
Stand by LED (1)
on the front panel
illuminates.
POWER button
The
POWER button (2)
on the front panel switches the 909 into operating mode or back
into stand by mode. In operating mode the
Stand by LED (1)
and the
POWER LED (3)
are
illuminated. In stand by mode only
Stand by LED (1)
lights up.
After switching to operating mode the protective circuits of the 909 take a few seconds to
check all circuits of the power amp before enabling the speaker outputs.
PROTECTIVE CIRCUITS
The protective circuits of the 909 operate outside the signal path. When the amp is on, these circuits constantly
check for errors with respect to temperature, DC offset and overload.
Temperature
In the event that one of the channels of the power amp exceed their maximum allowable
temperature the overheat protection switches off the output relays and the
POWER LED (3)
goes out. The unit is switched into stand by mode and the
ERROR display (4)
shows a 1.
As a precaution, we recommend to lower the volume and wait a while before turning the
909 back on by pressing the
POWER button (2)
. The 909 can only be switched back on
after the temperature has fallen below the allowable limit.
DC offset
If the DC voltage at the speaker outputs of the 909 exceeds the allowable limit, the speaker
relays will be switched off and the
ERROR display (4)
shows a 2. In this case we
recommend to lower the volume level. The 909 will re-enable the speaker outputs
automatically as soon as the DC offset falls within the allowable limit.
NOTICE:
If both errors (temperature and DC offset) occur at the same time, the
ERROR display (4)
shows a 3.
In both cases the upper error display refers to the right channel, the lower error display to the left channel.
Overload
If the current, which is flowing through the power transistors of the 909, exceeds the
allowable limit, the speaker relays will be switched off and the 909 automatically switches
into standby mode after a few seconds.
In this case we recommend to lower the volume level and check all connections from the
909 to the speakers. Usually a shorted connection is the reason for this error.
The 909 can only be switched back on by pressing the
POWER button (2)
