Spirit FOLIO SX mixer - Manual (Page 8)

Page 7
AUX OUTPUTS
The Aux outputs are on 3-pole ‘A’ gauge jack sockets, wired as shown on the left,
and incorporate impedance balancing, allowing long cable runs to balanced amplifiers and
other equipment.
CHANNEL DIRECT OUTPUTS
The Direct outputs are on 3-pole ‘A’ gauge jack sockets, wired as shown on the left,
and are unbalanced.
HEADPHONES
The PHONES output is a 3-pole ‘A’ gauge jack, wired as a stereo output as shown,
suitable for headphones of 200W or greater. 8W headphones are not recommended.
Polarity (PHASE)
You will probably be familiar with the concept of polarity in electrical signals and this
is of particular importance to balanced audio signals. Just as a balanced signal is highly
effective at cancelling out unwanted interference, so two microphones picking up the
same signal can cancel out, or cause serious degradation of the signal if one of the cables
has the +ve and -ve wires reversed. This phase reversal can be a real problem when
microphones are close together and you should therefore take care always to connect
pins correctly when wiring audio cables.
Grounding and Shielding
For optimum performance use balanced connections where possible and ensure that
all signals are referenced to a solid, noise-free earthing point and that all signal cables
have their screens connected to ground. In some unusual circumstances, to avoid earth
`loops’ ensure that all cable screens and other signal earths are connected to ground
only at their source and not at both ends.
If the use of unbalanced connections is unavoidable, you can mimimise noise by fol-
lowing these wiring guidelines:
l On INPUTS, unbalance at the source and use a twin, screened cable as though it
were balanced.
l On OUTPUTS, connect the signal to the +ve output pin, and the ground of the out-
put device to -ve. If a twin screened cable is used, connect the screen only at the
mixer end.
l Avoid running audio cables or placing audio equipment, close to thyristor dimmer
units or power cables.
l Noise immunity is improved significantly by the use of low impedance sources, such
as good quality professional microphones or the outputs from most modern audio
equipment. Avoid cheaper high imped-
ance microphones, which may suffer
from interference over long cable runs,
even with well-made cables.
l Grounding and shielding is still seen as a
black art, and the suggestions above are
only guidelines. If your system still hums,
an earth loop is the most likely cause.
Two examples of how an earth loop can
occur are shown on the right
Left Signal
Right Signal
Ground
Signal
Ground
Ground
Headphones
Monitor Outputs
Direct Outputs
Signal +
Signal -
Screen
Signal Send
Signal Return
Gnd/Screen
Tip
Ring
Sleeve
Mix Inserts
Mix & Sub Outputs
Aux Outputs
Mono Output
Audio (with ground connected)
Left Signal (with ground connected)
Right Signal (with ground connected)
Mains Earth
Earth Loop
Earth Loop
Supply Supply
Mixer
Example 1
Example 2
Mixer
Amplifier
Amplifier