User Manual

gain is increased, over the range 0dB to +12dB: this should be accompanied
by a ‘thickening’ and ‘warming’ of the audio signal, as more harmonic
distortion is introduced.
The red signal LEDs operate as a visual indication of output level, and are
calibrated at +8dB, +12dB, +16dB and +20dB respectively, making them
suitable for monitoring high level output signals such as those required to drive
a digital recorder or soundcard.
It is possible to cause the red LEDs to illuminate even if the Drive LED is not
lit. This situation can occur if the input gain is relatively low but the output gain
is relatively high.
4.7 90Hz Filter.
The high pass filter switch restricts the low frequency response of the preamp,
to effectively remove rumble or LF noise from the signal. The filter can be
useful in restricting “popping” on vocals or even low frequencies caused by
contact with microphone stands or microphone cables. Popping is an
undesirable thump that is caused by close-miking certain spoken or sung
letters, namely “P” or “B”. These particular letters cause a sudden expulsion of
air that can result in an audible thump. As this thump has a lot of low
frequency content the high pass filter can help to reduce the problem, as can
using a pop filter (a device usually made out of nylon material similar to
stockings) suspended in front of the microphone. The 90Hz filter is active on
both mic and instrument inputs.
4.8 Phase Reverse.
The phase reverse switch allows correction of a phase error, which may have
occurred in microphone wiring or placement. Phase errors can be due to two
microphones picking up the same signal at the same time. An example of this
problem is when recording a snare drum with one microphone on the top
snare skin and a second microphone on the underside skin of the snare drum.
Because the two microphones are picking up the same signal at the same
time, phase cancellation can occur. By inverting the phase of one of the
microphones this problem can be rectified. 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. The phase reverse is active on both mic and instrument inputs.
4.9 Instrument Input.
On each channel there is a front panel 0.25” instrument jack connector. This is
for connecting low level instruments such as electric guitars, basses, synths,
samplers, drum machines and acoustic pickups. The instrument input