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Section 29
The 'External Effects Loop'
Whilst the concept of an external effects loop is fairly
obvious to GT-5 owner, GT-3 owners are probably say 'Eh?
What loop? Well the GT-3 has one just as good as the GT-5
– only its hidden away under the OD/DS and is known as
'EXT OD/DS'. However, contrary to the name the EXT
OD/DS can be used for more than just distortions. Indeed,
both the GT-3 & GT-5 loops can be used for *any* external
mono effects device, and this includes external preamps.
The GT-5 naming of 'loop' describes this much better and
would have been more appropriate but c'est la vie.
The SEND and RETURN jacks on the back of the GT-3/5
provide the connections for the loop. This is a mono effects
loop only (AFAIK). So only a mono signal will be sent and
only a mono signal can be returned.
The GT-5 loop is bypassed when the effect is not switched
on and the same is true of the GT-3; the loop is bypassed
unless the OD/DS effect is turned on.
Both the GT-5 loop & GT-3 EXT OD/DS output a full
range signal to the SEND jack (20Hz-20kHz) – which will
come as a relief to some GT-3 owners who may have been
concerned that the frequencies were cut in the bass & highs
in the same manner the on-board distortions are.
The GT-3 has some additional tone shaping controls
useable with the external effects loop. It should be noted
that the treble, bass and level controls are all after the
RETURN and therefore in no way affect the signal sent via
SEND. They can however be useful for rough EQing of the
signal once back into the GT-3.
One more thing to watch with the loop is that the RETURN
impedance is only 220Kohm, so with more unusual set-ups
you may get an impedance mismatch problem. I think this is
most likely the problem I experienced with my Valvestate,
however even when quizzed Marshall failed to supply me
with ANY impedance information. Of course right
alongside impedance I must mention signal levels. It is also
possible in more unusual configurations to suffer from level
matching
problems—similar
professional studio equipment working on +4dBm whereas
semi-pro equipment uses -10dBV. Indeed, a check of the
specs shows the GT-3/5 effects loop at -10dBm. In essence
I think hooking up an amp (or an amps preamp) in the
effects loop is more fraught with problems than hooking up
a load of stompboxes. Especially when you consider that the
GT-3/5 loop really appears to have been designed with
stompboxes in mind.
Send Level Adjustment
There are no external output level knobs on the GT-3/5
AFTER the D/A converters. This means you must use an
© Copyright 2000-2002 Barry S. Pearce et al.
External Effects Loop
to
the
problems
with
internal level parameter to control the send level so as to
avoid clipping the external device's input.
On the GT-5 this is simple, as there is a parameter to
control the actual volume level of the SEND output. The
GT-3 however, does not have the direct ability to control
SEND level. However, this can be achieved simply altering
the output level of the effect immediately prior to the EXT
OD/DS in the effects chain.
Return Level Adjustment
Again, there are no external volume knobs prior to the A/D
converters. Therefore you must use the external device's
output control to ensure that the A/D converter on the return
path does not clip.
The GT-5 is now the poor man and does not provide a level
parameter to adjust the effects chain level – so use the
external device's output control to do this. However, the
GT-3 EXT OD/DS does provide a Level parameter and this
is used to control the effects chain level as described in the
section on level matching.
Level Matching
Level matching external devices is slight more complicated
than the internal effects on the GT-3/5. This is because you
have more level controls; there are those on the effects as
well as those on the GT-3/5.
To level match an external effect place the effect before the
input on the GT-3/5. Turn it on and off and use the external
effect's level control to match the on/off levels using the
GT-3/5's input meter. Use this same technique to level
match all the external effects you will use. Now, when you
place the effect(s) in the GT-3/5's send/return effects loop it
will give the same result on or off. You now have a stable
signal level within the loop. On the GT-3, use the level
control to match the output to your target effects chain
level.
Noise
I made a comparison of noise between a stompbox before
the GT-3 and inside the effects loop—and the external
configuration IS SIGNIFICANTLY NOISER (surprising as
the unit itself outside the GT-3 is very very quiet with an
SN
ratio
better
than
recommendation is: If you can prefer the internal effects
over and above ANY external effects unless you have to.
After all, the external loop itself is going to be slightly noisy
just by virtual of the fact that you are going through a
second set of DA and AD converters.
Creating Patch 'Ext FX Loop'
This patch is similar to clean except that you can plug other
devices/effects into the external effects loop on the GT-3/5.
This can be useful when trying to re-create the sound of an
–100dB).
Therefore
136
my
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