SPL TwinTube, User Manual

Page: 23 / 52

23
Analog Elemental Series
Preference Mic Pre | Control Elements
VU Meter
The VU meter displays the output level of the preamp. The gauge indicates levels from -20 dB
to +5 dB. If necessary you can lower the sensitivity by 10 dB so that the gauge goes up to
+15 dB output level (see “-10 dB” below and “About Leveling” on the previous page).
The VU meter is custom made to meet SPL specifications and assures a balanced optical
perception thanks to it’s optimized ballistics.
An especially interesting feature is the option to switch between two display modes: VU mode
and PPM mode. The VU mode (VU=Volume Unit) displays average levels, thus provides infor-
mation on the overall loudness. The PPM mode (PPM=Peak Program Meter) displays the peak
levels.
The integration time of the display complies with the BBC requirements. In VU mode the rise
time up to 0 dB is approx. 300 ms. In PPM mode the rise time up to 0 dB is about 2 ms and the
release time down to -20 dB is at a “slow” 1,5 seconds. This calibration ensures to display even
short peaks up to about +6 dB since the needle does not have to travel the entire distance of
the gauge every time.
PPM
The PPM button allows to switch the VU metering characteristics from VU display mode
(button is deactivated and not illuminated) to PPM display mode (button is active and illumi-
nated). A/D converter display also make use of the PPM mode. Monitoring peak levels is most
important to avoid overloading the converter and to prevent audible distortion. Peak levels
are always above the average levels. It may make sense in most cases to also press the -10 dB
button to prevent the needle from getting stuck on the right side of the gauge.
-10 dB
With this button you can change the sensitivity of the VU display. If you press the -10 dB button
(button is illuminated), the sensitivity of the display is lowered by 10 dB. With the needle for
example at 0dB, a value of +10 dB is displayed. Now you can read values of up to +15 dB.
You always have to add these 10 dB to the displayed values, for example if you compare these
values with those of an A/D converter. Remember that A/D converters show peak levels, not
average levels. For comparison press the PPM button to activate the PPM mode.
48 V Phantom Power Supply
The Preference Mic Pre provides 48 volt phantom power for microphones requiring external
current (generally condenser microphones). Such microphones are dependent upon a
clean, consistent and noise-free power supply for optimal operation and audio quality. The
Preference Mic Pre continuously delivers precisely 48 V and a maximum current of 14 mA,
which will power all microphones.
IMPORTANT: All microphones with balanced, ground-free outputs can be used with the
phantom power activated. Unbalanced microphones may only be used with phantom power
deactivated
.
Phantom power should only be activated when using microphones that require it. Please be
sure to deactivate phantom power with all other microphones (including tube microphones
which are supplied from their own power supply, thus need no extra phantom power supply).
ALWAYS FOLLOW THESE RULES WHEN WORKING WITH PHANTOM POWER – THE INPUT
STAGES OF THE PREMIUM MIC PRE CAN BE DAMAGED IF YOU DO NOT ACT ACCORDINGLY:
1. First connect the microphone to the Preference Mic Pre.
2. Then activate phantom power – you can start working now.
3. When you have finished recording, turn the phantom power off first.
4. DO NOT disconnect the microphone from the Preference Mic Pre UNTIL phantom power
has been switched off for a minute and all residual current is discharged.