AEA TRP3 Owner's Manual page 9

LOW CUT FREQUENCY FILTER
The TRP3's Low-Frequency filter (ref.#5) features two 6 dB per
octave slopes at 115 Hz and 230 Hz. This Low-Frequency filter is
intended to moderate the bass boost "proximity effect" inherent
with a ribbon microphone when used up close.
Directional microphones when moved closer on-axis to a sound
source become more sensitive to low frequencies. This proximity
effect becomes more pronounced the closer the distance. With
some Big Ribbon™ mics, such as the AEA R44C, proximity effect
begins at six feet and is extremely pronounced at a distance of
one inch. However, sometimes such strong low frequency content
can mask high frequency intelligibility. The TRP3's high-pass filter
helps diminish this low frequency energy. The frequencies of the
TRP3's high-pass-filter were specifically chosen to tame the
proximity on a variety of microphones in a variety of
configurations, especially AEA ribbon mics.
POWER SUPPLY
An external switching power supply with a grounded AC plug is
used with the TRP3 so hum fields can be kept away from the high-
gain electronics. The power supply allows the TRP3 to be used in
any country without any modifications made to the unit.
The power supply is a universal switching supply. It provides 3
regulated outputs +/-18.5 VDC and 52 VDC; these voltages are
then regulated internally again to provide clean power for the unit.
The power supply is not designed to be used in a wet
environment.
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