Here is what the manual has to say on the subject.
MTS Series
EFFECTS LOOP Operations
The MTS effects interface is the most versatile loop system you will find anywhere. There are two totally ndepenent loops, each
optimized for specific functions and applications.
1) SERIES LOOP:
Basically an insert patch point. When an external effect is patched into the send and return jacks, the path is interrupted
and 100% of the signal is routed through the effect. This puts some special demands on the effects unit. It must be essentially
transparent, meaning, it shouldn?t ?mess? with your tone. The input and output levels must be properly set for maximum headroom and lowest noise and it needs to operate at line level. Proper setting of the levels can be achieved using the following
method.
a) Set your amp/preamp volume levels for mormal playing levels. Connect a high quality instrument cable from the series loop
send jack to the effect input.
b) Adjust the effects unit input level to ?just peak? while playing your most aggressive licks.
c) Now connect another high quality instrument cable from the series return loop jack to the effect output.
d) Adjust the effects unit output level to the match the volume you heard before connecting the return cable. You can check this by
pulling the cable in and out of the return jack while playing and verifying there is no substantial volume difference. this is called
?UNITY GAIN?.
2) PARALLEL LOOP:
This is a more specialized loop. It has the advantage of maintaining your dry signal (it doesn?t mess with your tone), while
allowing you to mix in the amount of effect you want. The MTS parallel loop is a bit different. Most parallel loops found on guitar
amplifiers have a wet/dry mix control that turns down the dry signal (messing with our tone) while simultaneously turning up the
effects level. Our MTS parallel loop is unique because it never messes with your dry tone, and simply mixes in the amount of
effects using the effect knob on the front panel. Much like the effects buss on a mixing console. The direct signal remains
unaltered and the effects are simply mixed back in. There area few basic rules that must be adhered to and this also puts some
limitations on the uses for the parallel loop.
a)Your effects unit must be set for 100% wet. This means set the mix levels on the effect so that there is no dry signal passing
through the unit. Think of the mixing console again. You would not want to have any dry sigal going though the effects buss
because you would then be mixing in not only the effect but also the unwanted dry signal the comes out of the effects unit. Parallel Loop- cont.
This can even be derimental to your tone, because the dry output signal of many effects units is out of phase with the input.
Consequently, as you turn up the effects return knob, you may actually be mixing the ?Bad? out of phase signal back in with your
awesome dry signal... this is definitely now messing with your tone. Often loops on guitar amps are said to ?suck tone?. this ?tone
sucking? is more likely caused by improperly setting the effects mix than the loop design.
3) Now let?s discuss the specific uses, advantages, disadvantage and limitations of each loop.
a) The Series loop, by nature of the fact that it breaks the direct path and processes 100% of the signal, makes it so that
essentially any line level gadget will work. You can use echo, reverb, noise reduction, tremolo, equalizers, etc in the loop.
Remember to follow the procedure for setting for ?Unity gain?.
Advantages are: Works fine with just about any effect. No special requirements, other than the ?unity gain? settings, are
needed. Basically you can Plug in and Play.
Disadvantages: The entire signal passes through the effects unit and is more apt to mess with your tone.
b) The Parallel loop, on the other hand has more limited uses, but has the distinct advantage of not messing with your
tone. This loop is ideally suited for what are called ?time based effects?. This includes delay, reverb, chorus, flanging.
These types of effects work in parallel with your direct dry signal is always present. You cannot use effects that require
processing 100% such as equalizers, noise reduction/gates, tremolo or compressor/limiters.
Advantages are: Doesn?t mess with your dry tone. Easy to adjust the effects level with the front panel effects knob.
Disadvantages are: It has limited uses and may require reprogramming of your effects unit.
4) Special Notes:
a) A concern is the fact that many multi-effects units have a combination of all of the different effects. This mean, using
the parallel loop, you must be aware of which effects can and can?t be used. For ease of operation, we recommend using
the series loop if you intend to use a mix of different ?time based? and non- ?time based effects in one unit.
b) Both loops are for line level operation. Though some floor type and tabletop effects may work, the loops are designed
basically for rack mount type effects units. Not guitar level floor pedals. You will know an effect is not made for line level if,
when you plug it into the loop, you notice distortion and a loss of volume.
