Sometimes problems
will surface during set-up or sound-check,
and occasionally during the performance
itself. Even in fairly basic systems
there are plenty of opportunities for
something to go wrong: leads can get
pulled loose, batteries (even new ones!)
can die unexpectedly, and amplifiers can
overheat and shut down. Often the cause
of signal loss is trivial, although
catastrophic component failure can
happen.
1. Stay calm!
Panicking or losing your temper with
people or equipment will not make the
problem go away.
2. Focus your attention:
is the signal reaching its destination?
If not, why not.
3. Be methodical.
Don't change connections, leads and
components at random: work your way
along the signal path,
eliminating possible causes of failure -
see below - as you go. If you carry
spares (as you should!) you don't need
elaborate test equipment: you can always
find the culprit by substitution. If a
microphone isn't working, replace it
with one you know to be OK. If it still
doesn't work, replace the lead with one
you know to be OK (this also gives you
an opportunity to check you have it
connected in the right place). Obviously
your options are more limited if
something happens during the performance
- you need to be as inconspicuous as
possible - but that means you should be
more methodical, not less: don't mute or
unplug anything that might interrupt
what is happening on stage.
4. Be safe!
Electricity kills. Never take the
covers off live equipment (always
disconnect from the mains before you
take the cover off anything, especially
in a non-workshop environment). Never
replace fuses with any other conductor
(wire, nails, screws): if fuses keep
blowing, the equipment is faulty and
potentially dangerous. Never
bodge mains connections. Never
attempt repairs that need both hands
while you are hanging off a ladder.
5. Mark faulty equipment.
If you find a lead is faulty, don't just
put it back in the bag: mark it in some
obvious way (red tape is good for this),
put it to one side, and don't take it
out with you again until it has been
repaired and tested. The same goes for
everything else, from microphone to
mixer to monitor.
Use existing system
facilities as diagnostic tools: PFL
meters will tell you whether a signal is
reaching the desk (most desks also have
a headphone socket, so headphones are
useful for this too). Most offboard
equipment and most power amplifiers have
at least a "Signal Present" LED. Signals
can get lost because:
1. The signal lead isn't
plugged in, or has pulled
free, or is connected in the wrong
place. Labelling both ends of every
signal lead with a unique identifier -
makes it easier to tell which lead is
connected where. It is easy to make
mistakes in the dark or in a hurry, and
labelling is invaluable when it comes to
finding the mistake. Again, if the input
or output is pulled out of a processor
on a channel insert, the signal path
will be interrupted. Radio signals
(radio mics or in-ear monitors) need the
correct "virtual connection":
transmitter and receiver must both be
set to the same frequency.
2. Something in the signal
path has no power. Inputs can
disappear because of flat batteries,
power leads pulling out of preamplifiers
or foot pedals, or phantom power being
off when it should be on. If you are
using processors on inserts, check the
processor (it needs power too). It
should be fairly obvious if the desk or
a power amplifier is switched off.
Although fuses do occasionally fail for
no apparent reason, a blown fuse should
always be investigated further. Always
replace fuses with the correct type and
value. If you haven't a spare (why
not?), borrow one from less important
equipment as a last resort. With
equipment-specific fuses it is vital to
use the correct type: equipment fitted
with anti-surge fuses (marked with a
"T") will normally have a high initial
switch-on current, and a quick-blow fuse
(marked with an "F") of the same value
will blow at switch-on. If none of your
equipment seems to be working, check the
venue power supply.
3. Something is muted or not
routed. If the channel,
group, main busses or crossover outputs
are muted, the signal stops there. If
the signal isn't routed anywhere it will
go nowhere. If a signal that was there a
minute ago has disappeared, check you
haven't done anything to the channel
(like pressing the Mute button when you
meant to press PFL, or assigning the
channel to the wrong mute group). If the
signal is routed through a group or VCA,
the group or VCA fader needs to be up!
If you have lost it during the
performance, use your headphones to
check it is still reaching the desk:
some musicians use tuners that mute the
signal when the tuner is engaged, and
you don't want to mess with the mixer
connections or settings just because the
guitar is muted on stage!
4. Gain is too low.
If the Pad is down on the channel, or
the gain is at minimum, a weak signal
may be effectively unnoticeable (you may
also need to check the attenuation
switches on the D.I. box if you are
using one on that channel). If there is
a noise gate on the channel insert, the
signal may be lower than the gate's
threshold. If the channel, group or main
faders are down (or muted), or the power
amps are turned down, you probably won't
hear much from the speakers.
5. A cable is faulty.
99% of actual system faults (as opposed
to errors, as above) are caused by
faulty cables. Cables may fail at the
solder points (bad soldering and poor
strain-relief are the most common causes
of this: cheap cables and connectors are
a false economy), and although this
normally results in loss of continuity,
sometimes a loose end can make contact
with one of the other conductors,
causing short-circuit conditions. In the
worst case, this can cause failure of
the preamplifier or amplifier stage
driving it, or console damage where
phantom power is involved. Mains plug
and Speakon terminal screws can become
loose, and mains cables subject to
frequent flexing can eventually break
under the cable clamp.
6. Equipment has failed.
Fortunately, most modern touring
equipment is rugged and reliable, and
failure is rare. If it worked the last
time you used it, it probably still
works, unless:
-
It has been dropped;
-
It has been wet (from spills, immersion, rain, or
condensation. Garages in midwinter
are not ideal storage);
-
It has been hot (car boots in midsummer are not ideal
storage);
-
Somebody's two-year-old nephew has been pushing paper
clips into the ventilation slots.
If it is new, read the manual: although equipment
straight out of the box is occasionally
faulty, it is far more often supplied
with an array of controls and an
impenetrable menu that make it
impossible to use without first wading
through 100 pages of poorly-translated
gobbledegook.
If you can establish beyond doubt that a unit has
failed (for example, if the end of a
speaker cable produces sound from one
speaker but not from another), your
options are limited by what else you
have available.
Emergency fixes
• Failed Microphone/D.I.
Box. If you have no spares
(why not?!), decide whether you can
dispense with one: is one of the
backline instruments that you would
normally mic loud enough to get by? Is
the mic on the snare underside
essential? Or consolidate existing mics:
use a single mic to cover two sources.
For example, a pair of rack-mounted toms
(or two backing singers, or two
trumpets) could share one mic. If you
only have one mic (for vocals with solo
guitar, for example), it looks like an
"unplugged" session is in order. If your
only radio mic has failed, use a wired
mic: your singer's dance routine is
probably less important than the whole
gig.
• Failed Processor.
If you have no spare processor channels,
consolidate. Do without compression/EQ
on the least vital source. If a main or
monitor EQ has failed, decide which is
the most vital to the performance. It is
possible that one or more members of the
band can do without monitors, or perhaps
two or more can share a single monitor
send. Some system controllers (e.g. the dbx Driverack range) include EQ
and compression algorithms, and if these
are not already in use they can be used
for all Front-of-House processing. If
the monitor feeds need a lot of EQ
because of feedback considerations,
consider backing everything off
by a few decibels to make up a bit of
headroom.
• Failed Effects Unit.
Don't do the song with the timed
delay on it. The venue probably has
enough reverb of its own.
• Failed Mixer.
Most systems with a separate monitor
desk (a "spare" in an emergency) travel
with experienced crew, who will know
what to do. Channel failure is of minor
consequence if you have spare channels.
If the whole mixer has failed and it is
your only mixer, you are in trouble.
Your best bet in that case - if you can
get away with it - is to let the
backline cope as well as it can, while
trying to get the main vocals up to a
usable level for the power amps. Most of
the plastic-box speakers that have
built-in power amps will accept mic
inputs, so if you are using these you
can plug the mic straight into one, and
link to any others. A
Behringer Shark, if you have one,
will get you from mic to line-level.
Otherwise, try running the vocals
through a D.I. box (you'll need a
battery-powered or passive D.I. if the
desk has gone down) into anything that
can accept low-level inputs and provide
a useful amount of gain. Some
compressors and other processors can
achieve this. Daisy-chain processors, if
you can't get enough gain from one on
its own.
• Failed
Crossover/Controller. Unless
you have active monitors or multiple amp
racks you probably don't have a spare.
In a standard two-box system, if you
have anything with a sweepable high-pass
filter you can use this to roll the bass
off the feed to the mid/high speakers.
Some graphics and parametrics have
sweepable shelving high and low filters
that will do for this. If in doubt, set
the filter to a slightly higher
frequency than your normal crossover
point. A lot of bass bins have limited
high-frequency output by design, so you
can probably get away without a filter
on the bass feeds in an emergency (you
might need to cut a bit of the low-mid
on your equalisers to compensate). Also,
some have
inbuilt passive crossovers, which can be
switched in to act as low-pass filters.
If you don't have Z-leads or splitters,
run everything in mono and use the left
mixer channel for the bass feed and
right channel for the mid/high feed.
Otherwise, split the signal from the
mixer's outputs, running one half of the
split straight to the sub amp and the
other half through the high pass to the
mid/high amp. If your
crossover/controller has limiters that
are normally in use, remember to use
more caution than usual with mixer
output levels.
• Failed Power Amp.
There are several ways to go. Dispense
with a couple of monitors, and use the
monitor amp for Front Of House (unless
it is a monitor amp that has failed, in
which case just dispense with the
monitors). Or run everything in mono,
using one half of a power amp to run the
subs and the other half to run the
mid/high speakers (you can also do this
to restore your monitors if a monitor
amp fails and - unaccountably - the
musicians think what they hear is
more important than what the audience
hears). Watch speaker impedances when
doubling up: some subs are 4Ω, so
running two off one power amp channel is
Not Recommended. If necessary, run a
single sub, and back the mid/high off by
3-6 dB. If you are already running in
mono and don't have enough amplifiers,
try dispensing with the subs and
limiting the PA to vocals.
• Failed Speaker.
If you use the same speakers for
monitors and Front Of House, use one of
the monitors to replace it if is a main
speaker, or do without it if it is a
monitor. If you use different speakers
for each application, you might still be
able to use a pair of monitors as Front
Of House speakers as long as their HF
pattern is more or less acceptable (with
speakers at left and right of the stage,
a matching pair is preferable).
• Failed Sub.
Back off the mid/high by a few decibels
and manage with one less sub. If your
subs are normally placed together you
may need to back off as much as 6 dB
from the mid/high speakers to
compensate. If you normally place them
either side of the stage, 3 dB will
probably be enough.