Randall RM100, Owner'S Manual

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 effects 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.