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Section 9
This section was written quite a long time ago – at least as
far as my equipment, rig and set-up are concerned. My rig
has now changed significantly, none more so than in the
studio/recording environment. I am also using more hi-tech
techniques for noise elimination that I do explain a little of
in a small description that I have added to the end.
However, the principals presented here remain sound (no
pun), and are probably more representative of most users'
set-ups than my new set-up is. Thus, although this section
has now been edited, much of my equipment described here
is as it was when I originally wrote the piece. That said I
hope you still find the following information useful.
What Causes Noise?
Noise can be generated from a number of sources.
Humbuckers will be quieter than single coils, ground loops
can introduce noise, hum or interference into a set-up, and
an impedance mismatch can ruin your sound too. Some
devices and stompboxes may be noisy. This is especially
true where high gain is used. It is important to be aware
that compressors, limiters, and fuzz/overdrive/distortion
will accentuate the problem. Sometimes something as
simple as the routing of signal cables near transformers or
alongside power cables is often to blame.
Eliminating the noise is very important; it will interfere with
the sound, making it sound muddy, and it will make you
unhappy, as you can't get a 'professional' sound. Oh and its
even worse when you record and listen to it! Don't worry;
the chances are it will be solvable! We will be looking at
noise removal extensively. Showing you how to find it, and
how the GT-3/5 can help by creating a patch called 'Noise
Check'. We will also be tracking down and removing
unwanted distortion.
Ground Loops
Ground loops are also known as earth loops or induction
loops. A ground loop occurs when there multiple paths to
earth are available. For instance we have two effects earthed
(grounded) to the electricity supply and a shielded cable
running between the two. There are now two paths to
ground (earth) et voila—you now have a ground loop.
Ground loops can introduce unexplainable noise, hum or
interference into your system.
The first thing to do if a ground loop is suspected is to
eliminate other causes of hum. You need to be sure a
ground loop is the problem. Following the noise elimination
process detailed below, will help you identify these
situations.
Let's say we have two effects, with the casing earthed, and
thus the cable shield on both goes to earth. You now have
two paths from effect 1 to earth. Firstly down its own earth
cable, and secondly down the shield of the linking cable to
© Copyright 2000-2002 Barry S. Pearce et al.
Noise Elimination
effect 2 and then down effect 2's earth! This problem can
also manifest itself as crosstalk. Other interference is
possible in such situation the ground loop acts like an
aerial!
Craig Anderton gives a detailed explanation of why a group
loop occurs in his book 'Guitar Gadgets'. What I will do
here is merely provide the means to solving it.
The most effective way to solve a ground loop is the break
the shield in our signal cable. Although we now have a
break in the shield the cable is still screened by it, and one
end is still connected to ground. The easiest way to do this
is in the cable connector. Make sure you do this properly
though, breaking only ONE end in this manner and make
sure it cannot re-connect! Don't leave a bit of cable
flapping! This is also the cheapest method. You could buy a
special cable for this but it is far simpler to do this yourself.
It is possible to do this on cables with moulded connectors
but heck; most good quality cables don't use moulded ends.
It is also a somewhat more difficult procedure, and I'd
rather not encourage it. Suffice to say the easiest way is to
chop of the connector and replace it with a new one that you
solder yourself.
If you put one of these broken ground cables in place and
the hum gets worse instead of better, then put the original
cable back. Your problem here is a lack of direct connection
from the effect to ground.
So the idea here is any device that has 3 mains wires (one of
which is earth) which connects to another device that has 3
mains wires should have between the two a broken shield
cable. If between these two 3-wire devices you have a two-
wire device place the broken shield cable in the chain
immediately prior to the second three-core cable. This will
prevent ground loops.
An alternative, sounder approach is to use the 'GND LIFT'
or 'Ground Lift' feature of some devices, although such
features normally only appears on rack units or DI's.
One way to help identify these problems is to draw a block
diagram. First drawn in your amp, effects units, guitar and
so on, in the order they appear in your chain. Draw in the
signal cables between them. Then drawn in a line about 2
inches above all this. Label it 'GND'. For each device with a
3 wire mains lead, draw a line from the unit to the GND.
You should now have a very easy way of identifying
possible ground loops. Oh. If you have a rack with a metal
assembly, then draw a line 2 inches below and label this
'Rack'. Then draw a line from each unit in the rack to this
line IF the unit has some form of metal-metal contact. For
most equipment this contact is made by the faceplate of the
unit being screwed (metal) onto the rack. I hadn't done this
when I started checking for noise below. I wish I had,
possible ground loops would have been easier to spot.
46
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