8
Using the Clarett OctoPre
Combo Inputs
All eight of the analogue inputs use “Combo XLR” connectors. These can accept male XLR connectors,
TS (unbalanced) ¼” jacks or TRS (balanced) ¼” jacks.
When an XLR connector is used, the pre-amp automatically configures gain and impedance to receive
microphone level signals. If a ¼” plug is used, the pre-amp is able to accept balanced or unbalanced
line level signals. When INST mode is selected (on Channels 1 or 2), the 1/4” input reconfigures again
to optimise for an unbalanced, high impedance signal.
Pre-amp Gain
The GAIN of each channel should be adjusted to suit the incoming level. Obviously “hotter” sources
will need a lower gain setting. Always use the LED meters to check the signal level on each channel.
Start with the GAIN control set to minimum. Ask the performer to play at the loudest level required
by the song, and gradually increase the gain until the meter shows orange (-3 dB). Then lower the
gain by a few dB. This should ensure that the signal level is unlikely to ever reach red (0 dB) and
overload the A-to-D converter, which would result in distortion.
Note that the high headroom pre-amplifier design used in the Clarett range means that a
switchable Pad is unnecessary. (See “Performance Specifications” on page 16 for input sensitivity
specifications.)
The red O/L LED should never illuminate; if it does, the gain is set too high.
Phantom Power
The two 48V switches apply 48 V phantom power to Mic inputs 1 to 4 and 5 to 8 respectively. Phantom
power is required by most condenser (capacitor) microphones, and also active ribbon microphones.
Phantom power is only applied to the XLR contacts of the Combo connectors: thus if a group of
four inputs is being used for both mic and line (or instrument) level signals, phantom power is only
applied to the microphones.
Dynamic microphones do not require phantom power, but most will operate normally with phantom
power supplied. Passive ribbon microphones do not require phantom power and may be damaged if
supplied with phantom power.
If you are unsure about a microphone’s type, DO NOT apply phantom power without checking the
manufacturer’s specifications first.
Line Outputs
By connecting the line outputs of the Clarett OctoPre to the analogue line inputs of a mixing console
(or any other device), the unit can be used either as a purely analogue, 8-channel microphone pre-
amplifier, or as an analogue “break-out box” for ADAT signals when in ADAT
>
LINE mode.
The outputs are balanced; see [20] on page 7 for the pinout. Ready-made D25-to-XLR or
D25-to-jack breakout cables are available from professional audio suppliers. The maximum output
signal level is +16 dBu.
