Addendum #1 :- Using Channel and Output Pre-fade insertions.
An optional feature for the Audio Sidecar, which can be factory or distributor retro
fitted, is line level and balance pre fade insertions for the channels and 2T bus outputs.
These involve fitting a new, hinged, rear panel that contains the insert circuit boards. A
new bottom panel is needed to give clearance to the rear panel as it swings down, and a
special bus circuit board is used with connections to the insertion circuit boards. This
information is only relevant if a non-insert Aurora Sidecar needs to be retro converted to
the insert option.
The pre fade insertion consists of two 1/4” TRS jack sockets, both carrying a balanced
line level signal, with the upper jack the pre fade insertion send and the lower jack the
pre fade insertion return.
Between the two TRS jack sockets is a toggle switch which, if set to the left, totally
bypasses the insert circuitry (the TRS jacks are non functioning) while, if set to the right,
engages the insertion circuitry. This enables a user to switch in or out a device
permanently connected to the insertion jacks and, in the very rare likelihood of a
component failure, allows the circuitry to be totally bypassed.
Above and below the input and output XLR connectors are small holes allowing access
to trim potentiometers that adjust the gain of the amplifiers connected to the TRS jack
sockets. The upper trimpot sets the insertion send level while the lower trimpot sets the
insertion return level.
Connecting the TRS jacks to unbalanced devices :-
All audio paths entering or exiting the TRS jack sockets are electronically balanced and
unity gain. If the channel input gain is set at 0dB, the channel fader set at 0dB and the
input signal is +4dBu, the insert send and return levels will be +4dBu as will the channel
output.
Balanced circuitry is used in professional audio because of the noise canceling it
provides on long cable runs, especially cables that run alongside ac power cables whose
magnetic fields can be induced into the audio cable.
Unbalanced cabling does not
provide this protection.
When connecting unbalanced equipment, special care has to be taken to avoid ground
loops because ground is part of the signal path.