grace design m801
mk2
owner’s manual
7
Preamplifier Operation
SETTING THE GAIN
First, turn the gain control fully counter-clockwise and check that the +48V phantom power is off.
Connect a microphone and then turn on the phantom power if required. When sending a signal to a
recorder, converter or interface that has fixed input levels, simply increase the gain until the optimum
recording level is reached. If the peak indicator flashes red excessively with the gain control in the
fully counterclockwise position, engage the -20dB attenuator.
When sending a signal to any recording device with an input attenuator, use the following proce-
dure: With the sound source present, turn the gain control clockwise until the peak LED begins flash-
ing red, then reduce the gain until the red stops flashing. Since red indicates a peak level which is
12dB before preamplifier clipping (6dB in unbalanced mode), it is OK for it to come on periodically
during recording. If peak indicator flashes red excessively with the gain control in the fully counter-
clockwise position, engage the -20dB attenuator. Now adjust the recorder input control for the opti-
mum recording level.
RIBBON MIC MODE
Pressing the ribbon switch optimizes the m801mk2 channel for ribbon microphones by boosting
the gain by 10dB while disabling 48V phantom power and increasing the input impedance. Before
activating ribbon mic mode, make sure the channel’s gain is fully down (counter-clockwise) and 48V
phantom power is off. Now simply press the ribbon switch and turn the gain control upwards until
the proper recording level is achieved.
If you press the 48V phantom switch while the ribbon switch is engaged, nothing will happen. If the
48V phantom power switch is turned off and then the ribbon switch is turned on the preamplifier
will wait until the phantom power voltage has completely discharged and then the ribbon mode will
activate automatically. An additional benefit of the ribbon mic mode is that the input DC blocking
capacitors are relay bypassed to further simplify the m801mk2’s signal path. Incidentally, the ribbon
mode works very well with lower output dynamic microphones as well.
Maintenance
The model m801mk2 was designed to be maintenance free for many years. It is highly unlikely that
your unit will require service. However, there are two adjustments that may need to be made from
time to time. These procedures should be made only by a qualified service technician or the Grace
Design factory.
PEAK LED ADJUSTMENT
The peak LED threshold levels may be adjusted to a user defined operating level. This circuit is set
at the factory with the green threshold at -14dBu and the red threshold at +16dBu. The relationship
