Sound Devices 302 - Manual (Page 9)

302 User Guide and Technical Information
9
Phantom and T- Microphone Powering
This switch selects the type of power that will be applied to the adjacent input XLR. The
302 provides both Phantom and T-power on each channel respectively. If neither Phantom
or T-power are required, with dynamic microphones for instance, it is good practice to turn off
microphone powering (DYN position).
Phantom Power
Phantom powering is a fixed DC voltage between 12 and 48 volts. This voltage is resistively applied
to pin-2 and pin-3 of an XLR connector relative to pin-1. There is no voltage difference between the
signal pins-2 and -3. Dynamic microphones will operate as normal when phantom power is applied
to them.
The 302 can provide up to 10 mA to each input at 48 V, sufficient for the most power-hungry
condenser microphones. Many phantom powered microphones do not require 48 V and can be
properly powered with 12 V. When acceptable, use 12 V phantom to extend the 302’s battery life.
The phantom voltage level can be set to either 12 V or 48 V and is applied across all inputs where
phantom power is selected.
T-Powering
T-powering is a microphone powering scheme used by several European condenser microphone
manufacturers. Today, T-powered microphones are not as common as phantom powered
microphones, but many are still in regular use. Unlike phantom power, T-power resistively applies
12 V between the signal pins -2 and -3. The 302 provides positive T-power, on the three-pin XLR
connector pin-2 has +12 volts relative to pin-3. T-power can be selected for each input.
When using “red dot” T-powered microphones (reverse polarity T-power) use a polarity-reversing
adapter on the input, otherwise damage to the microphone may occur.
Phantom and T-powering are not interchangeable. Use T-powering only for T-powered microphones.
The DYN (dynamic) position does not apply any voltage to the microphone input. It is generally
good practice to select the DYN position when microphone power is not required. Phantom power
can capacitively couple noise into the mic inputs with poor mic cables. Do not apply phantom power
when using ribbon microphones, improperly wired cables can permanently damage the microphone.
High-Pass Filters
Each channel of the 302 has a two-position high-pass filter. High-pass (or low-cut/low roll-off)
filters are useful for removing excess low frequency energy in audio signals. Wind noise is a
common unwanted low frequency signal and a high-pass filter is effective for reducing wind noise.
For most audio applications engaging the high-pass filter is beneficial, since little usable audio
information exists below 80 Hz, especially for speech reproduction.
The 302’s high-pass filters feature a 12 dB/octave slope with either 80 Hz or 160 Hz corner (-3 dB)
frequencies. The 160 Hz settings is used when aggressive filtering is required. The 302’s high-pass
circuit is unique because of its placement before any electronic amplification. Most mixer’s high-
pass circuits are placed after the mic preamp, where all of the high-energy low-frequency signals get
amplified. Because the 302’s circuit cuts low-frequency signals before amplifying, higher headroom
is achieved in presence of signals with a lot of low-frequency energy.