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ART MPA Gold™ Microphone Preamplifier
In the "normal" (OUT) position, the tube distortion gradually rises until it smoothly clips.
The tube is run almost completely open-loop in this mode, providing a musical tube
"crunch" when overdriven with a natural recovery from clipping. The tube section can be
more easily overdriven when the gain switch is in. This mode brings out the harmonics
in the input sources, particularly stringed instruments.
The tube circuit runs extremely clean in the "high" (IN) position of the plate voltage
switch. As signal levels rise distortion remains very low until within 6dB of clipping,
where the overload characteristics smoothly limit the signal swing. There is increased
bandwidth (>100KHz), and headroom in this mode as well.
Meter switch
The analog meters monitor the output signal at the output. The switch selects the
sensitivity of the meter.
0VU on the meter measures +4dBu at the output jacks in the "+4dB" position.
Depressing the switch changes 0VU on the meter to become –10dBu at the output
jacks.
Tube Warmth Meter
The LED meters monitor the operation of the tube section. The meter reads both the
average and peak level. Average levels are shown as a histogram. Peaks are held for
one second by a single LED. In "normal" plate voltage mode "0" on this meter indicated
less than 5dB of headroom, and a great deal of tube warmth. Monitor the average levels
to gauge the tube warmth, as most of the peak levels held are so short they contribute
little to the perceived warmth. In "high" plate voltage mode there is more tube circuit
headroom. "0" on the meter indicates less than 10dB of headroom.
Front Panel Connections
Instrument Inputs
The ¼" jacks on the front panel serve as an instrument input. The input impedance is
always >1M Ohm and the gain can be adjusted by the Input gain control. The maximum
input signal level is +17dBu (5Vrms) @ minimum input gain.
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