Allen&Heath 21 Series - Manual (Page 11)

8
f) MONO MASTER FADER
Controls the output level of the mono mix.
This mix is a mono sum of the main stereo output, is derived
after the left/right master faders, and therefore depends
upon their position for output level.
PFL select is available to check the signal supplying the
mono output for level and quality.
g) MONITOR SECTION
This section selects the signals available for headphone
monitoring via the top panel socket and/or for control room
monitoring via the monitor output socket on the rear.
There are separate volume controls for headphones and output
to amplifier.
Selecting PFL in any section of the mixer
will override the monitor outputs.
The three monitor source select buttons (Mono, Stereo, Tape)
can be used in permutations described as follows:
BUTTONS DEPRESSED MONITOR OUTPUT
Mono only Mono mix
Stereo only
Tape only
Stereo mix
Return from stereo tape machine,
connected to "Tape In" socket on rear
panel.
Mono Stereo Stereo mix
Mono + Stereo + Tape Stereo tape return
Stereo + Tape Stereo tape return.
The VU meters, except when any PFL function is selected, will
follow the selected monitor source.
We suggest, as a normal procedure, that the Mono button be
left depressed. This will allow simple switching between
Mono and Stereo by operation of the stereo button alone.
Similarly, as can be seen from the above priority table,
both Mono and Stereo buttons can be left depressed whilst
operating the Tape button for A-B checks.