TL Audio VP-1 - Manual (Page 11)

4.5 Pad.
When activated, the pad switch will reduce the Mic input gain by 30dB. This is useful
when dealing with high level mic input signals, such as those produced when
recording loud sources with sensitive microphones (drums are a typical example).
Without the pad, it’s possible to overload the input stage in these circumstances,
causing audible distortion. Activating the pad switch will cure this.
4.6 Phantom
Power.
This switch applies 48V phantom power to the mic input, allowing the VP-1 to be
used with condenser microphones.
CAUTION: Operation of the phantom power switch, or plugging a microphone in
with phantom power applied, may cause a click or thump in your loudspeakers. To
prevent this happening, ensure that the system gain is set to minimum (e.g. on your
mixing console fader or power amplifier), before operating the switch or plugging in a
microphone.
4.7
Drive and Peak LEDs.
The yellow Drive LED provides a visual indication of the signal level through the
valve stages, and therefore the extent of “warming” or valve character being
introduced. The drive LED will gradually illuminate as the input level or gain is
increased, over the range 0dB to +12dB.
The red Peak LED operates as a conventional warning that clipping is about to occur.
The operating level of both input and output stages is monitored, and the LED
illuminates when there is less than 5dB of headroom remaining.
If the output gain control is set to its centre position (0dB) then the Peak LED will
illuminate some 8dB after the Drive LED has reached its full intensity. However, it is
possible to add gain further down the chain (the output level control provides up to
15dB of gain), which will cause the Peak LED to illuminate at a lower level of Drive.
This situation implies that a high level of “clean” signal is present, without driving the
valves at a high level.
Normal operation would be to set the input gain so that the Drive LED is illuminating
regularly, with occasional illumination of the Peak LED occurring on loud transients.
4.8 Expander/Gate
Section.
The Expander/Gate circuit is located post the preamp stage, just after the rear panel
insert point. The VCA based gate design is very precise and responsive, and operates
by monitoring the signal level and expanding the level down by around 80dB if the
signal is below the level selected on the rotary threshold control, effectively muting it.