Millennia M-2B Transformerless Vacuum Tube Stereo Microphone Preamplifier - Manual (Page 6)

M-2b
M-2b FRONT PANEL
(1) GAIN TRIM "GAIN TRIM 0 - 12 dB"
Conductive plastic rotary potentiometer offering a gain trim range of 12 dB. Working in con-
sort with range switches (2) and (3) below, the Gain Trim allows fine adjustment of microphone
gain. When fully CCW, there is no additional gain added (0 dB). When fully CW, an additional
gain of approximately 12 dB is realized.
(2) MEDIUM RANGE SWITCH ("MEDIUM GAIN RANGE")
The first of two pushbutton switches used to select the gain range of the M-2b preamplifier. See
below (3) for complete description.
(3) HIGH RANGE SWITCH ("HIGH GAIN RANGE")
The second of two pushbutton switches (2) and (3) used to select the gain range of the M-2b
preamplifier. These two pushbutton switches define three preamplifier gain ranges, as follows:
a.) LOW RANGE: When both switches (2) and (3) are not depressed and corresponding LEDs
are not illuminated, microphone preamplifier is set to "Low Gain Range." Low Gain Range is
defined as approximately 14 dB to 26 dB, adjustable by the Gain Trim control (1) above.
b.) MEDIUM RANGE: When switch (2) is depressed and switch (3) is not depressed, micro-
phone preamplifier is set to "Medium Gain Range." Medium Gain Range is defined as approxi-
mately 26 dB to 38 dB, adjustable by the Gain Trim control (1) above.
c.) HIGH RANGE: When switches (2) and (3) are both depressed and corresponding LEDs are
both illuminated, microphone preamplifier is set to "High Gain Range." High Gain Range is
defined as approximately 38 dB to 50 dB, adjustable by the Gain Trim control (1) above.
(4) HIGH VOLTAGE DPA (B&K) MIC INPUT SELECT "+130V"
Routes the optional DPA (Bruel & Kjaer) microphone input to the microphone preamplifier.
High voltage supply is not effected by this switch (e.g., the +130 VDC supply is always present
on pin 3 of the optional four pin mic input XLR irrespective of where this switch is set).
(5) PHANTOM POWER SELECT "+48V"
Routes +48 VDC "phantom" voltage to the 3-pin XLR microphone inputs for use with all con-
ventional phantom powered microphones. If "DC Option" has been installed, and this switch is
not depressed, the conventional front end becomes entirely DC coupled — an ideal match for
ribbon mics, moving coil mics, and so forth.
(6) POLARITY REVERSE "PHASE"
Pushbutton switch which, when depressed and corresponding LED is illuminated, flips the mi-
crophone polarity (output becomes 180 degrees out of phase with respect to the input). When
switch is not depressed, microphone signal remains in phase from input to output.
(7) POWER SWITCH "POWER"
Rocker switch for switching AC line power on and off.