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ART Digital MPA™ Microphone Preamplifier
The 1/4" instrument input is NOT affected by this control, and remains high (>1M Ohm) imped-
ance.
Analog Output control
The output signal level at the rear output jacks is adjusted by this control. It can provide from
+10dB of gain (fully clockwise) to completely muted. You can see the effects of this adjustment
reflected in the analog meters when the meter switch is set to "output".
HPF control
The HPF is a single tuned High Pass Filter that is frequency tunable. The input signal can be
filtered to remove "pops" or other extraneous low frequency information. This control moves the
rolloff frequency from 10 Hz (fully CCW) to 200 Hz (fully CW). Since it is single tuned (the same
as single pole, the simplest kind of filter), it preserves some low frequency content so its use is
less obtrusive. It is especially useful in close mic'd applications.
Gain switch
The Gain switch is used in conjunction with the input gain control to adjust signal levels through
the DMPA. When depressed, the tube circuit provides 20dB more gain in the signal path. This also
has the effect of driving the tube harder and making the tube the dominant source of gain and
overload character.
Phantom switch
Phantom power on the microphone input is turned on and off with this switch. Depressing the
switch will power condenser microphones and other 48volt phantom powered devices. Phantom
power is supplied to pins 2 and 3 of the input jack.
NOTE:
1) Dynamic microphones are NOT affected by Phantom power, although it should be turned off when using dynamic
microphones or line level inputs.
2) Although the 48volt phantom power ramps up and down slowly it may still create a pop. Mute the output of the
DMPA when engaging or disengaging phantom power to prevent damage to equipment following the DMPA.
Phase switch
The Phase switch can invert the phase of the audio signal path in either channel. The Phase
switch is located after the tube circuit in the signal path, so you can hear slight differences be-
tween different phase selections in the "normal" plate voltage mode near saturation. There are a
number of reasons why adjusting the phase is needed these include, wiring errors and inversions
in some audio equipment. Some microphones sound different depending on the phase chosen.
If two microphones are out of phase, they may cancel at various frequencies (depending on the
distance between them). If this happens, try changing the phase of one of the microphones and
see if there is an improvement.
Plate Voltage switch
This switch sets both the tube bias point and the plate voltage level the balanced differential tube
circuit runs at. The amount of headroom is adjusted by using the Gain switch and the input Gain
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