SoundCraft EFX User Manual page 9

Headphones
The PHONES output is a 3-pole 'A' gauge jack, wired as a stereo output as shown, ideally
for headphones of 150Ω or greater. 8Ω 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 always take care 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
or ground '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 minimise noise by follow-
ing these wiring guidelines:
•
On INPUTS, unbalance at the source and use a twin screened cable as though it
were balanced.
•
On OUTPUTS, connect the signal to the +ve output pin, and the ground of the
output device to -ve. If a twin screened cable is used, connect the screen only at
the mixer end.
•
Avoid running audio cables or placing audio equipment close to thyristor
mer units or power cables.
•
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 impedance microphones, which may suffer
from interference over long cable runs, even with well-made cables.
Grounding and shielding is still seen as a black art, and the suggestions above are only
guidelines. If your system still hums, an earth/ground loop is the most likely cause. Two
examples of how an earth loop can occur are shown below.
Under NO circumstances must the AC power mains earth be disconnected from the
14
dim-
Warning!
mains lead.
Soundcraft EFX/EPM User Guide Issue 1110
PROBLEM SOLVING
Basic problem solving is within the scope of any user if a few basic rules are fol-
lowed.
•
Get to know the Block Diagram of your console (see page 14).
•
Get to know what all controls and/or connections in the system are supposed
to do.
•
Learn where to look for common trouble spots.
The Block Diagram is a representative sketch of all the components of the console,
showing how they connect together and how the signal flows through the system. Once
you have become familiar with the various component blocks you will find the Block
Diagram is quite easy to follow and you will have gained a valuable understanding of
the internal structure of the console.
Each component has a specific function and only by getting to know what each part is
supposed to do will you be able to tell if there is a genuine fault! Many "faults" are the
result of incorrect connection or control settings which may have been overlooked.
Basic Troubleshooting is a process of applying logical thought to the signal path through
the console and tracking down the problem by elimination.
•
Swap input connections to check that the source is really present. Check both
Mic and Line inputs.
•
Eliminate sections of the channel by using the insert point to re-route the signal
to other inputs that are known to be working.
•
Route channels to different outputs or to auxiliary sends to identify problems
on the Master section.
•
Compare a suspect channel with an adjacent channel which has been set up
identically. Use PFL to monitor the signal in each section.
•
Insert-point contact problems may be checked by using an insert bypass jack
with tip and ring shorted together as shown below. If the signal appears when
the jack is inserted it shows that there is a problem with the normalling contacts
on the jack socket, caused by wear or damage, or often just dirt or dust. Keep
a few in your gig tool box.
If in doubt please contact Soundcraft customer support.
PRODUCTS UNDER WARRANTY
UK customers should contact their local dealer.
Customers outside the UK are requested to contact their territorial distributor who is
able to offer support in the local time zone and language. Please see the distributor
listings on our website (www.soundcraft.com) to locate your local distributor.
OUT-OF-WARRANTY PRODUCTS
For out-of-warranty consoles purchased in the United Kingdom, please contact the
Customer Services Department (e-mail: soundcraft.csd@harman.com) at the factory
in Potters Bar, Hertfordshire: Telephone +44 (0)1707 665000.
For all other out-of-warranty consoles, please contact the appropriate territorial dis-
tributor.
When mailing or faxing please remember to give as much information as possible.
This should include your name, address and a daytime telephone number. Should
you experience any difficulty please contact Customer Services Department (e-mail:
soundcraft.csd@harman.com)
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