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Needless to say I have done this now to confirm what I have
done!
As a final note—prefer the use of GND LIFT or broken
ground cables...
ANY ATTEMPT TO REMOVE THE EARTH FROM
A
POWER
SUPPLY
INCLUDES PLUG CHEATS – 3 PIN PLUGS
WITHOUT THE EARTH WIRED. YOU MAY WELL
INVALIDATE
THE
WARRANTY
AND
SOMEONE
ELSE'S
DECIDE.
PLEASE REFER TO APPENDIX F FOR MORE TIPS
ON ELECTRICAL SAFETY.
Clipping
As defined in section 2, clipping alters the sound you hear,
manifesting itself as anything from clicks or crackles
through speaker rumble through to distortion. In fact the
principle of clipping is behind every distortion or fuzz we
have today. However, there are times when this clipping is
undesired—this is unwanted distortion. For instance we
want a nice clean warm sound. Any clipping that occurs will
cause distortion and will ruin our clean sound. Indeed, even
when using a distortion digital clipping is clearly audible
and seriously mars the sound.
Impedance Mismatch
Impedance seems to be cause for concern, but most
manufacturers of modern equipment know what we want
and how we are likely to set it up, so these days impedance
problems are less common. Having said that, given the
number of increasing complex cabling systems people are
using including the 4/5 cable methods that many GT-3/5
users use, impedance must be treated with respect.
In general your guitar should always feed a high-impedance
input (>100k ohm), thus providing a low loading on the
guitar pickups. The GT-3/5's input is 1M ohm—so no
problems there. A 100-220k ohm input is an acceptable
compromise between a lack of loading and a lack of noise
(high impedance inputs can generate noise and are
susceptible to RF interference).
Generally, a device with a given output impedance should
drive a device whose input impedance is at least 10 times
that of the output. Therefore 10k ohm driving 100k ohm is
good, 10k driving 10k is bad. It should also be noted that 1k
can feed 100k without a problem.
If your guitar sounds muddy, thin, and loaded down you
may have an impedance problem. For more information I
suggest reading 'Guitar Gadgets' by Craig Anderton.
© Copyright 2000-2002 Barry S. Pearce et al.
IS
DANGEROUS.
MANUFACTURERS
PLACE
YOUR
LIFE
LIFE
IN
DANGER.
Noise Elimination
Cables
First up we are going to check ALL your cables. Including
those between your amp and the speaker cab (if you have
such an arrangement—i.e. a stack). If the cables are suspect
THIS
we could have problems checking everything else. One
word of wisdom first; buy the best cables you can afford.
Try to ensure that all unbalanced cables you use are 20ft or
under. Any longer you will be liable to RF interference and
OR
signal loss. For all noise checks I am assuming that you are
YOU
using unbalanced cables of this length or less, fitted with
1/4" jacks.
To check a cable properly you will need a multi-meter. One
with crocodile clips on the ends of the probes would make
life easier.
There are three things we need to check:
1. Continuity of the signal path
2. Continuity of the shield
3. Short-circuit between the shield and the signal path
All these tests can be performed using either a continuity
test setting or a resistance measurement. I will say that a
continuity tester usually uses an audible monitor it is far
easier
to
CONNECTED TO ANYTHING WHEN PERFORMING
THESE TESTS!
To check continuity of the signal path
Place each meter probe on the 'tip' of the jack. Then waggle
the cable where it goes into the connector and down the
length of the cable to the other connector, and waggle the
cable where it enters it. If you are using a continuity test you
should hear no break in the sound. If you are using
resistance measurement, resistance should remain at 0 (at
the most it should remain < 1ohm). Any deviation from
these results means you have a break in the cable.
To check continuity of the shield
Now place the probes on the shield side of the jack.
Perform the same test as for the tip. Results should be
checked for and interpreted in the same manner.
To check for a short-circuit between the shield and the
signal path
Now place one probe on the tip and one on the shield.
Perform the same test. The difference here is that a
continuity tester should not make any sound. If it does you
have a short. If measuring resistance, resistance should
Section 9
Noise Elimination
use.
DO
NOT
HAVE
THE
CABLES
47
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