Boss GT-X - Section29; External Effects Loop; The External Effects Loop; Send Level Adjustment

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Section29ExternalEffectsLoop
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©Copyright2000-2002BarryS.Pearceetal.  136
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.
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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.
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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.
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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.
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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.
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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 to the problems with
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
internallevelparametertocontrolthesendlevelso asto
avoidclippingtheexternaldevice’sinput.
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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.
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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.
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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 –100dB). Therefore my
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