Microplane Stereo Amplifier LUNATEC V2 User Manual

OWNERS MANUAL  
LUNATEC V2  
MICROPHONE PREAMPLIFIER  
PO Box 204 Boulder, CO. 80306  
voice: 303.443.7454  
fax: 303.444.4634  
Revision A December, 1998  
© Copyright 1998, Lunatec LLC  
 
FRONT PANEL CONTROLS  
GAIN CONTROL Each gain control has 11 positions and adjusts the voltage gain from  
10dB to 60dB in 5dB steps.  
TRIM CONTROL The trim control provides 10dB of continuously variable output  
attenuation. In the fully clockwise position the trim is at unity (no attenuation). In the fully  
counter-clockwise position the trim is at -10dB. For reference, the 3 o’clock position is -4dB  
and the 12 o’clock position is -8dB. The trim control should be left in the fully clockwise  
position during normal recording.  
PHANTOM POWER This switch provides 48 volts to power condenser microphones. The  
phantom power switch (labeled +48) connects the +48V power supply to pins 2 and 3 on  
the XLR input connector. Alternatively, the V2 can be configured to provide 12V Parallel  
power. Please contact the factory for information on this option.  
PEAK INDICATOR The LED peak indicator, which monitors the signal between the input  
and output amplifiers, illuminates the green LED at -14dBu and illuminates the red LED at  
+16dB (10dB before clipping).  
HIGH PASS FILTER (labeled HPF) Sometimes referred to as a bass roll-off, the HPF uses  
a three position toggle switch to select two different low cut corner frequencies and an OFF  
position. Position 1 is the higher cutoff frequency and Position 2 is the lower cutoff  
frequency. Internal jumpers allow for selection of either 6dB/octave or 12dB/octave slope.  
The cutoff two frequencies can be set at 50Hz/100Hz or 75Hz/125Hz. Selecting HPF  
switch position 1 sets the roll-off to the higher frequency while switch position 2 sets the  
roll-off to the lower frequency. The 12dB/octave filter employs a transitional Thompson-  
Butterworth response for the best combination of passband flatness and time domain  
response. See section II for detailed jumper setting information.  
POWER SWITCH The power switch connects power from the DC input connector to the  
preamplifier circuitry. If the preamplifier is connected to a charged battery or other DC  
power supply the POWER LED will illuminate.  
POWER LED Indicates that the V2 is turned on and connected to an adequate power  
source. NOTE: The 6 Volt V2 automatically turns off if the battery or power source voltage  
drops below 5.5V. The 12 Volt V2 automatically turns off if the battery or power source  
voltage drops below 11.0V.  
LOW BATT For the 6 Volt V2 the low battery indicator flashes if the battery voltage drops  
below 5.75V. For the 12 Volt V2 the low battery indicator flashes if the battery drops below  
11.5V.  
3
 
CONNECTING THE PREAMPLIFIER  
AUDIO CONNECTIONS  
Input connections are made using female XLR connectors. These are wired with pin 2  
positive, pin 3 negative and pin 1 ground. 48V phantom power, if used, is supplied on pins  
2 and 3.  
Output connections are made using male XLR connectors or RCA phono jacks. The XLR  
connectors are wired with pin 2 positive, pin 3 negative and pin 1 ground. Use the RCA  
phono jacks for unbalanced output. If the XLR outputs are to be used unbalanced, a  
modified cable is required and pin 3 should be left open. See figure 2 below. The XLR and  
the RCA outputs can be used simultaneously.  
HOT  
2
1
GND  
SHIELD  
3
(OPEN)  
Figure 2. UNBALANCED OUTPUT CABLE TERMINATION  
POWER SUPPLY CONNECTIONS  
A four pin XLR connector is used for the DC power input of the V2. The V2 can be ordered  
to operate from either 6 or 12 Volt power sources. Pins 1 and 2 are ground and pins 3 and  
4 are either 6 or 12V DC. To avoid compatibility problems it is recommended that 6 Volt  
systems be wired to use pin 3 for hot (+6v) and pin 2 for ground while 12 Volt systems  
should be wired to use pin 4 for hot (+12v) and pin 1 for ground. The V2 current draw  
ranges from .38A to .62A depending on the microphone used.  
4
 
OPERATION  
SETTING THE GAIN  
Turn the gain control fully counter-clockwise, turn the trim control fully clockwise and check  
that the +48V phantom power is off. Connect the microphone to the preamplifier and then  
turn the phantom power switch on if required. When sending a signal to a tape recorder  
that has fixed input levels, simply increase the gain until the optimum recording level is  
reached.  
When sending a signal to a tape recorder with a variable input use the following procedure:  
Turn the gain control fully counter-clockwise, turn the trim control fully clockwise. 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. 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.  
The trim control can be used for ultra fine output level adjustment as well as for level riding  
during recording. It should be noted that the maximum output level of the preamplifier is  
reduced by the amount of output attenuation being used. For instance, if the trim is set to -  
6dB the maximum output level of the preamplifier will drop from +26dBu to +20dBu. Since  
the LED peak indicator monitors signal level before the trim control it will always monitor  
the actual preamplifier headroom regardless of the trim control setting. It is best to leave  
the trim control fully clockwise for normal recording operations. This ensures that the  
preamplifier will be operated at the minimum necessary gain setting.  
USING THE V2 IN M-S MODE  
In MS mode the preamplifier accepts the Mid signal in channel 1 and the Side signal in  
channel 2. The channel 1 output (XLR or RCA) provides the “sum” of the inputs and the  
channel 2 output (XLR or RCA) provides the “difference” of the inputs. In the MS mode the  
CH 1 GAIN control adjust the amount of Mid signal in the “sum” and “difference” outputs.  
The CH 2 GAIN control adjusts the amount of SIDE signal in the “sum” and “difference”  
outputs. It is best to leave the TRIM controls at “0” and use the gain controls to adjust the  
stereo field. Equal gain on both channels will provide the widest stereo perspective while  
reducing the gain of the SIDE channel will decrease the width of the stereo field.  
5
 
BATTERY CONSIDERATIONS  
With a standard pair of 48V condenser microphones the V2 draws roughly .48A. In our lab  
we have tested the V2 with an ECO-CHARGE Beta 6V 7.2A/h battery system. The V2  
shuts down automatically after 13+ hours with a pair of Countryman Isomax II microphones.  
Note that this represents a complete discharge of a new and completely charged battery  
and if used in this fashion repeatedly the battery would degrade rapidly. 10 hours would be  
a conservative estimate.. A simple formula to determine useful battery life in hours is  
Hours= C ¸ .7 where C is the capacity of the battery in Amp-Hours. We have set the LOW  
BATTERY threshold so that the LED begins flashing after about 8 hours of run time (or  
about 5 hours before shutdown) to encourage the user to avoid deep discharges.  
However, no two batteries have the exact same discharge characteristics so the low battery  
threshold may represent different levels of reserve for different batteries.  
The V2 can be set at the factory to run at 6 or 12V. The current drain is the same at either  
voltage but the total power consumption will be twice as high for the 12V system. Also, it is  
normal for a 12Volt V2 to run warm to the touch.  
JUMPER SETTINGS  
In addition to the front panel controls, the Lunatec V2 has several options that can be  
selected with internal jumpers. Before making any changes to the internal jumpers always  
disconnect any power source from the V2, switch both +48 switches to the on position and  
wait for 1 minute before removing the top cover. This is to assure that all power has been  
discharged from the capacitors used in the power supply circuit. Refer to Figure 3 on page  
6 for jumper locations for preamplifiers with serial number #V054 and below. Refer to  
figure 4 for preamplifiers with serial number #V055 and above.  
STEREO-MS MODE The V2 operates in a standard 2 channel stereo mode as well as MS  
or Mid-Side mode. Jumpers J7 and J17 select the mode.  
HIGH PASS FILTERS J5 and J6 select the filter slope for CH1. J18 and J19 select the  
filter slope for CH 2. J9 and J10 select the frequency range for CH 1. J15 and J20 select  
the frequency range for CH 2.  
HIGH PASS FILTER JUMPER SETTINGS  
J9,J10,J15,J20  
LOW  
HIGH  
HPF SWITCH  
POSITION  
1
2
1
2
CUTOFF  
100Hz  
50Hz  
125Hz  
75Hz  
FREQUENCY  
Table 1. HPF Filter Frequency Selection  
6
 
Figure 3. Circuit Board Jumper Locations SN #V054 and below  
Figure 4. Circuit Board Jumper Locations SN #V055 and above  
7
 
SPECIFICATIONS  
EIN  
@60dB gain  
<130dB  
FREQUENCY RESPONSE  
+/- 3dB @60dB gain:  
6Hz-250kHz  
THD+N  
+20dBu out @20dB gain  
+20dBu out @40dB gain  
+20dBu out @60dB gain  
0.0011%  
0.0011%  
0.0046%  
INTERMODULATION DISTORTION  
@40dB gain +25dBu out  
<.0025%  
<-130dB  
<8°  
NOISE - REFERRED TO INPUT  
@60dB gain 50 Ohm source  
PHASE DEVIATION  
50-20Khz  
CROSSTALK  
Either Channel  
-109dB  
CMRR  
@60dB gain, 3.5Vcm, 1KHz  
@60dB gain, 3.5Vcm, 10KHz  
Output CMRR  
80dB  
97dB  
60dB  
MAXIMUM OUTPUT LEVEL  
Balanced  
+27dB  
Unbalanced  
+21dBu  
IMPEDANCE  
Input  
Output  
Minimum Load Impedance  
1600Ohms  
150Ohms  
600Ohms  
WEIGHT  
2.4lbs (1.1kg)  
DIMENSIONS  
L5.5” x W8.3” x H1.6”  
POWER CONSUMPTION  
500mA DC 6-12V  
8
 

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