8
input (select mic on the frontpanel mic/line switch). This circuit is totally transparent and is perfectly suited to this
application.
All outputs are active all the time, so you have the possibility of up to 5 live outputs if your source is MIC IN, or 3 live
outputs if your source is LINE IN.
Operating Microphone Preamplifier
SETTING THE MIC PREAMPLIFIER GAIN
1. If you are using the m103 with a microphone signal, it is recommended that you start with the EQ and COMP
sections turned off. This will simplify the process of setting proper operating level of the mic preamplifier.
2. Turn the GAIN control fully counter-clockwise, set the TRIM control at 12 o’clock (no boost or cut) and check that the
+48V phantom power is off.
3. Connect the microphone to the m103 mic input and then turn on the phantom power switch on if required. When
sending a signal to a recorder that has fixed input levels, simply increase the gain until the optimum recording level is
reached.
4. When sending a signal to a recorder with a variable input, use the following procedure: Turn the gain control fully
counter-clockwise, set the trim control at 12 O’clock. Set the record level control on the recorder to 12 o’clock
or midway between minimum and maximum. With the sound source present, turn the preamplifier gain control
clockwise until the peak LED begins flashing red, then reduce the gain until the red stops flashing.
NOTE: since red
indicates a peak level which is 10dB before clipping, it is OK for it to come on occasionally during recording. Adjust the
recorder input control for the optimum recording level.
USING THE TRIM CONTROL
The trim control can be used for fine output level adjustment as well as for level riding during recording or gain makeup
after the compressor section. The trim control can add (or subtract) an additional 10dB of gain for a total maximum
preamplifier gain of 75dB. If the trim control is not needed for riding gain, providing extra gain boost or makeup gain
from the compressor, then it should be left at zero (12 o’clock).
USING RIBBON MIC MODE
Activating the ribbon switch does three things: 48V phantom power is locked out to prevent potential damage to
ribbon microphones, phantom decoupling caps are bypassed, and the impedance of the mic input is raised from 8.1kΩ
to 20kΩ. The m103 has ample available gain, sufficient for even the most demanding low-level recording scenarios with
ribbon microphones.
USING THE HPF
The high pass filter, sometimes referred to as a bass roll-off, starts at 75Hz. This 12dB/octave filter employs a transitional
Thompson-Butterworth response for the best combination of passband flatness and time domain response. Most
common uses for this are in situations where low-end rumble from mechanical sources or wind are present, to reduce
excessive proximity effect, or to simply help reign in excessive bass during recording.
Operating the EQ Section
The m103 equalizer section has 3 bands, with a fully parametric mid section and sweepable low and high sections. This
equalizer has been crafted to be very powerful and versatile with no compromise to the transparency and detail of
the signal. Because of its high level of precision and accuracy, you may find yourself being able to hear a much smaller
amount of cut or boost than you would with other EQ designs.
Both the low and high sections can be operated in either peak or shelf mode. Peak mode, as indicated by the bell
shaped icon, is used to cut or boost a specific frequency. Shelf mode, as indicated by the shelf icon, boosts or cuts all of
the frequencies above (for the HI band) or below (for the LOW band) the frequency selected.
