supply current to the m9XX to rapidly rise above the maximum current which a computer or
external USB power supply can deliver.
If an over-current condition occurs, the m9XX's processor will detect it, immediately mute the
audio and turn off the internal audio power supplies. This will protect the m9XX from damage and
prevent it from drawing excess current from your computer or power supply. When this happens
the LED display will indicate OC (Over Current) momentarily. Once the over-current condition is
removed, the m9XX audio power supplies will be turned back on and music will resume.
While this does not hurt the m9XX, it is good practice nonetheless to mute the audio (push down
once on the volume knob) or pause your playback source while plugging or unplugging
headphones.
Line Output Operation
The RCA phono line output jacks are provided to connect the m9XX to an amplifier, powered
speaker system, or preamplifier. Use RCA interconnects to connect from the m9XX to the
unbalanced line inputs of your external device. These outputs follow the volume / mute control. A
volume level of 90 is “unity gain” and will allow the m9XX to produce a 2V output signal for a 0dBFS
digital input signal.
The signal feeding the rear panel line out jacks is "normalled" through the right hand headphone
jack. This is so that if you have speakers connected to the line outputs, they will mute when you
plug headphones into the right hand jack. If you want to hear speakers and headphones at the
same time, simply use the left hand jack. Note that the crossfeed circuit feeds these connectors.
When listening to loudspeakers you may want to turn crossfeed off.
Volume and Mute Control
A high quality, light action stepped rotary encoder is used for volume and mute functions. Turn the
knob clockwise to increase volume, counterclockwise to decrease the volume. A single push and
release will mute all outputs. When the unit is muted, the 7 segment LED will dim and pulsate to
indicate mute is active. Another single push and release de-activates mute. The m9XX attenuator is
a hybrid design. Most of the volume control duties are handled in the digital domain with 32 bit
processing but there are two analog gain ranges as well. This allows a full 99dB of volume control
range, preserves a very low noise floor for IEMs, and allows high peak output voltage for low
efficiency planar magnetic phones.
Crossfeed Circuitry
A completely analog crossfeed circuit electronically simulates the signal crossfeed that occurs in a
natural acoustic space. The crossfeed function can be switched on or off from the Setup Menu.
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