9
User Guide and Technical Documentation
Phantom Power
Microphones requiring phantom power should use the lowest voltage ac-
ceptable to maximize MixPre battery life. Condenser microphones that can
operate on phantom voltages from 11–52 volts will not have a performance
benefit with 48-volt phantom; therefore 15-volt phantom is appropriate.
The 15-volt setting will increase battery life versus the 48-volt setting.
Microphones requiring 48-volt phantom will not operate, or may oper-
ate with lower headroom and increased distortion at the 15-volt setting;
therefore use 48-volt phantom for these mics. Consult your microphone
documentation.
Dynamic microphones do not require phantom power. A properly connect-
ed balanced, dynamic microphone will not be affected by the presence of
phantom power nor will it draw any current. However, it is good practice
to turn phantom power off when not needed. Poor or incorrectly wired
microphone cable can cause audible artifacts in microphone signals. Some
wireless receivers outputs are adversely affected by the presence of phan-
tom power, therefore, consult the wireless receiver documentation.
High-Pass Filter
The two-position high pass (low-cut) filter in the MixPre is useful for
removing excess low frequency energy in audio signals. This excess energy
can be caused by multiple sources, including wind noise, vibration, unidi-
rectional proximity effect, or high ambient noise levels. The 80 Hz position
is appropriate when recording general speech, music, and ambient sound.
The 160 Hz position is useful to enhance speech clarity. The MixPre high
pass circuit topology is unique in that the filters are placed immediately
after the input transformer, before any active gain circuitry. This gives the
MixPre higher headroom with low frequency signals, as the low frequency
signals are not amplified before they are removed, as in most other designs.
The high pass filter is a single pole design (slope of 6 dB per octave) and
uses high quality film capacitors for very low distortion. The high pass
filter switch controls both inputs. The center position of the switch removes
the filter from both audio paths.
When possible, attempt to equalize at the sound source with microphone
selection, use of windscreens, shock mounts, microphone placement, and
onboard microphone filtering. Multiple high pass filters (filters on micro-
phones and on the MixPre) will give an additive effect, increasing the slope
of the filter.
Headphone Monitoring and Tape Return
Headphone monitoring is an essential need in production audio. The Mix-
Pre enables monitoring of program (mixer) audio or a second audio source.
In normal operation the headphones monitor the output bus directly. Using
