Peak LED.
Each channel is equipped with a red LED, which is intensity modulated to indicate the
signal level in the valve stages. Reducing the input gain will result in the peak LED
illuminating later. However, reducing the output level will have no affect on the peak
LED, although it will, of course, reduce the output signal level.
The LED starts to illuminate with a pre-fade level (i.e. before the output level control)
of +6dBu, and is fully illuminated at +16dBu. At this point there is still 10dB of
headroom left, so it is quite acceptable to drive the unit such that the peak LED is
illuminated brightly on loud peaks, in order to exploit the valve character of the
circuitry.
90Hz Filter.
The high pass filter switch restricts the low frequency response of the pre-amplifier, to
effectively remove rumble or LF noise from the signal. The filter is a second order,
12dB per octave design, with a -3dB point at 90Hz, which has been developed to
remove unwanted noise and improve intelligibility without affecting vocal or bass
instrument programme content.
Phase Reverse.
The phase reverse switch allows correction of a phase error, which may have occurred
in microphone wiring or placement. A phase mis-match will probably manifest itself
as an apparent loss of bass content when two microphone signals are mixed together
or fed to a stereo pair of loudspeakers. If an error is suspected, it is a simple operation
to check by phase reversing each channel in turn.
Output Level.
The output level control acts a continuously variable attenuator on the output of the
channel. The output of the pre-amplifier is capable of +26dBu, which is sufficient to
directly interface and fully modulate a digital multitrack for direct to tape recording.
This technique is gaining in popularity as a means of recording a very high quality
signal prior to mixdown, avoiding the noise and colouration added by recording
through a mixing console.
In other applications, such as feeding into a console or signal processor, a much lower
output level will be required. The output level control allows precise control and
fading of the signal without affecting the operating level - and therefore signal quality
- in the pre-amplifier.
