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Preamplifier Gain The SmartMixer has a substantial gain range, allowing it to accept a wide variety of microphones. However, if in some instances higher-output microphones are used for close talking, it may be necessary to reduce the preamplifier gain. This can be done by changing switch settings inside the unit. With the unit unplugged from its AC source, remove the two screws on each side of the unit and carefully lift off the top cover. Locate the internal switches designated on the circuit board by “SW2,” “SW8,” “SW14” and “SW20” (Figs. 4 and 5, page 11). A “control map” drawing will be found on the inside of the top cover. Changing the settings of these internal switches will cause a gain reduction of 10 dB for channels 1, 2, 3 and 4 respectively. The preamplifier gain may be reduced further, allowing the SmartMixer to accept line-level sources. Changing the settings of the internal switches designated by “SW3,” “SW9,” “SW15” and “SW21” will cause an input reduction of 50 dB for channels 1, 2, 3 and 4 respectively. Note that the appropriate internal switches can be used in combination for a total sensitivity reduction of up to 60 dB for each channel. Output Level The SmartMixer’s output is factory set at line level. Should mic-level output be desired, simply unplug the unit, remove the top cover and locate the switch on the circuit board marked “SW26” (Figs. 4 and 5, page 11). Changing the setting of this switch will cause a 50 dB reduction in output. Phantom Power Each of the SmartMixer’s inputs supplies +48V DC phantom power. Should it be required to disable the phantom power, simply unplug the unit, remove the top cover and locate the switches designated on the circuit board by “SW1,” “SW7,” “SW13” and “SW19” (Figs. 4 and 5, page 11). Changing the settings of these switches will disable phantom power on channels 1, 2, 3 and 4, respectively. Note that, although they do not require phantom power for operation, most balanced-output dynamic microphones can be used without disabling the SmartMixer’s phantom power. Output Level LED Meter The Output Level LED meter is factory set to indicate RMS output. Should peak output indication be desired, simply unplug the unit, remove the top cover and change the setting of the switch designated on the circuit board by “SW27” (Figs. 4 and 5, page 11). “Zero” (0) level is factory-calibrated at +4 dBm into 600 ohms. Function Summary of Internal Controls Ch 1 Ch 2 Ch 3 Ch 4 Output 48V Phantom Power 10 dB Input Atten. 50 dB Mic/Line Atten. Limiters (on/off) “Off” Atten. Range Preamp Output Gating Limiter Thresholds “Off” Atten. Adjustment NOMA Meter RMS/Peak SW1 SW2 SW3 SW4 SW5 SW6 VR2 VR3 -- SW7 SW8 SW9 SW10 SW11 SW12 VR5 VR6 -- SW13 SW14 SW15 SW16 SW17 SW18 VR8 VR9 -- SW19 SW20 SW21 SW22 SW23 SW24 VR11 VR12 -- SW26 SW25 SW27 Figure 3. Summary of internal controls 10 Rear Panel SW27SW25SW26 Front Panel Figure 4. Internal view of mixer. Mic Mic Mic Mic SW3 SW9 SW15 SW21 Line Line Line Line Line Phantom 40 dB Phantom 40 dB Phantom 40 dB Phantom 40 dB SW26 Outpu t SW1 SW2 SW7 SW8 SW13 SW14 SW19 SW20 Mic Off 30 dB Off 30 dB Off 30 dB Off 30 dB Off Off Off Off SW6 SW12 SW18 SW24 Gating Gating Gating Gating VR3 VR6 VR9 VR12 –20 dB –20 dB –20 dB –20 dB Min. –6 dB SW5 Min. –6 dB SW11 Min. –6 dB SW17 Min. –6 dB SW23 –40 dB –40 dB –40 dB –40 dB VR2 VR2VR2 VR5 VR8 VR11 – ––1 110 dB 0 dB0 dB +10 dB +10 dB+10 dB –10 dB +10 dB –10 dB +10 dB –10 dB +10 dB On Meter SW27 NOMA SW25 Peak RMS Off SW4 SW10 SW16 SW22 On Off On Off On Off On Off Figure 5. Detail of internal controls. 11 Adjusting ”Off” Attenuation In instances when the number of microphones in use is high, it may be necessary to increase the amount of “off ” attenuation per microphone to keep the total ambient noise level low. There are “off ” attenuation adjustments inside the unit. To adjust the “off ” attenuation of channel 1, unplug the unit, remove the top cover and locate the trimpot designated on the circuit board by “VR3” (Figs. 4 and 5, page 11). It is factory set at approximately 8 dB, the attenuation at the middle of the control’s rotation. When the control is turned fully counterclockwise, “off ” attenuation is approximately 20 dB. Conversely, when the adjustment is turned fully clockwise, “off ” attenuation is approximately 6 dB. VR6, VR9 and VR12 control “off ” attenuation for channels 2, 3 and 4 respectively. Changing the settings of the switches designated on the circuit board by “SW5,” “SW11,” “SW17” and SW23” will extend the range of “off” attenuation to –40 dB for channels 1, 2, 3 and 4 respectively. Preamp Outputs Each microphone channel has an independent unbalanced preamp output that is separate from the main mixer output. This is helpful when it is necessary to record the output of each channel, whether or not it is the active mixer output (as is required, for example, in some courtroom proceedings). As set at the factory, no gating is applied to these outputs. To gate these outputs, unplug the unit, r...