Most
band's never look after (or don't know how to look
after) their stuff. The most common failures are:
1) Bad cables,
either speaker cables and loose or dry joint soldered
plugs or instrument/mic cables simply ready to fall
apart and held together by pure luck. If you can't
solder very well yourself, get someone who can to
make sure your jacks and connectors are done right.
Also, cables should ALWAYS be put away correctly
after a gig, i.e. coiled up in a loop fashion and
neatly put it away. Never tie cables in knots and
simply throw them in a bag as this will place too
much stress on the cable itself and it will
eventually break down (usually when you need it
most).
2)
Amplifiers that need a good clean, i.e.
the fan filters need a good blast out with compressed
air and the whole amp insides cleaned out. Dirt in
the filter can seriously cause your PA amp to
overheat and eventually burn out. That's a very
expensive mistake to make, never mind about the
embarrassment of loosing your singer through the PA
amp going up in smoke at a gig. Get your amp cleaned
every 6 months if you can.
3) PA Speaker
impedance's driving too low causing the amp to
overheat or cut out. Most PA amplifiers (not guitar
or bass amps) can be driven down to 4 ohms minimum
per side. This is the lowest impedance your amp can
run safely (read the instruction book for details or
ask an engineer). There are some amps that will go to
2 ohms minimum, but you'll need to pass higher
currents through the speaker cable making them more
likely to break down. Also a 2 ohm impedance needs
short speaker cables to drive correctly i.e. the
cable itself has impedance which adds to the speaker
impedance and you loose power!. Some manufacturers
claim that their amps will be ok at 2 ohms, some
simply don't handle this low impedance and overheat
causing a PROTECT LED to show and shut down the amp.
A simple rule - no less than 4 ohms per side (4 to
the left and 4 to the right in total). That could be
made from 2 of 8 ohm cabs wired together (in
parallel) which halves the impedance to 4 ohms, and
the same for the other side.
4)
Amplifier/Speaker power combination incorrect. This
is a common fault with some setups I've seen. This
can either simply mean your PA amp is under powered
(can cause tweeter damage due to the amp distorting
and sending nasty spikes to the HF driver), or it
goes the other way and too much power blows the
speakers up! As a rule, your PA amp should be
something like at least a 3rd more than that of the
speaker rating. This is referred to as 'head room'
For eg; a speaker with a power rating of 500 watts
RMS (never read peak or music power values, they are
a marketing ploy to make it look better on paper!),
would need a power amp of about 700 watts. You'd
probably use between 600 watts and 800 watts in
practice. Making the power amp more powerful than the
speakers ensures a clean signal even at high volumes.
Too much power will destroy the speaker drivers. If
you used a 1000 Watt amp driving the same 500 watt
speaker, yes it would be great and totally clean, but
at high levels, dangerous. So be careful.
5) Valve guitar
head/combo impedance set incorrectly. This again is a
common fault where the head or combo speaker output
impedance is set incorrectly. You MUST set the
impedance of any valve amp to match exactly the same
as the speaker cab you're using. DO NOT mix cabs and
speakers, mixing speaker cabs together will cause the
total impedance to lower, and if the valve amp is not
set correctly, then extensive damage will occur to
the output valves (EL34) and the output transformer
itself...very expensive indeed to fix. If you have a
speaker cab with no markings on the back informing
you of it's impedance, then DON'T USE IT, get it
checked out and then you can plug it in safely, you
must know what it's impedance is before plugging it
in. If you have a transistor amp, this problem
doesn't occur as the amp can run into anything down
to 4 ohms!..no less than that mind you.
6) Keep equipment
dry and clean - this generally goes a long way to
keeping it working well. Whether in the studio or on
the road, it's worth keeping this in mind. Dirt and
moisture attacks electronics. If you do have problems
with soldering plugs or anything else, consult an
engineer you can trust, it may be the best money you
ever spend. It's peace of mind at a gig!...
Lastly
and most importantly - ALWAYS make sure your mains
cables are wired correctly - think safety first
!!!!!! it's not worth getting electrocuted on stage
just for a gig. Death is not an option! Things to
watch out for are loose mains plugs (check the cable
grips and screws for tightness), splits or frays in
cables - go through your gig bag of cables and get
them repaired NOW by a qualified person... don't just
leave it like that, one day it may get you. If you
live in the UK or any other country that uses the
earth pin in the mains plug, ALWAYS have this earth
connected, especially on amplifiers and desks. Beware
of using so called 'earth lift' plugs where the earth
wire is disconnected to clear an earth loop hum. Yes,
it will cure the hum, but it won't protect you from
an electric shock!. ALL equipment must be earthed for
safety. Besides, the hum can be cured in other ways.
If you get an earth hum from connecting your desk or
PA to a guitar or bass amp on stage, use a D.I box in
line, rather than going straight into the amp. The
D.I or Direct Inject box has a dedicated Earth Lift
switch just for this job, and it's safe.
Check your gear - and
live to use it!
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