Radial Engineering Ltd.
EXTC 500 Module
True to the Music
®
OVERVIEW
The Radial EXTC is a professional audio interface that takes a balanced line level signal and
converts it to a guitar-level effects loop and then re-converts it back to a balanced line level
for processing. In other words, you send in a balanced signal from your recorder, adjust the
send level that drives the pedals. Set the return level from the pedals as it comes back and
send the resulting sound to your recording system.
OUTPUT
OUTPUT
EXTC
INPUT
SEND
RETURN
RETURN
PEDAL
PEDAL
PEDAL
EXTC
INPUT
SEND
OUTPUT
PEDAL
PEDAL
PEDAL
POLARITY REVERSE
POLARITY REVERSE
POLARITY REVERSE
180°
INPUT
RETURN
PEDAL - A
PEDAL - B
PEDAL - A
PEDAL - B
BLEND
EXTC
OUTPUT
INPUT
SEND
SEND
RETURN
BLEND
EXTC
POLARITY 180°
PHASE
CANCELLATION
NORMAL
PHASE
NORMAL
PHASE
NORMAL
PHASE
Although simple in principle, the key to the EXTC’s performance is how quietly it does the
task. This is achieved by employing full sized discrete electronic components, class-A circuitry
and transformer isolation to help eliminate the hum and buzz that is common with pedals and
guitars. The other cool ‘trick’ inside the EXTC is the blend control. This mixes the original dry
signal with the newly introduced effects created by the pedals. Something to think about here
is how some effect pedals will reverse the polarity of the signal passing through them. When
you mix a dry signal with a wet signal and one is polarity reversed, you will of course end up
with cancellation. The diagram below illustrates a setup where one pedal “B” is inverting the
polarity creating cancellation where two out-of-phase signals come together.
OUTPUT
OUTPUT
EXTC
INPUT
SEND
RETURN
RETURN
PEDAL
PEDAL
PEDAL
EXTC
INPUT
SEND
OUTPUT
PEDAL
PEDAL
PEDAL
POLARITY REVERSE
POLARITY REVERSE
POLARITY REVERSE
180°
INPUT
RETURN
PEDAL - A
PEDAL - B
PEDAL - A
PEDAL - B
BLEND
EXTC
OUTPUT
INPUT
SEND
SEND
RETURN
BLEND
EXTC
POLARITY 180°
PHASE
CANCELLATION
NORMAL
PHASE
NORMAL
PHASE
NORMAL
PHASE
The 180º polarity reverse switch plays an important role by ensuring both the dry and wet
signals are in phase. The next diagram shows how the 180° switch inverts the signal before
it gets to the offending pedal. Pedal “B” gets tricked into re-inverting the signal back to normal
phase.
OUTPUT
OUTPUT
EXTC
INPUT
SEND
RETURN
RETURN
PEDAL
PEDAL
PEDAL
EXTC
INPUT
SEND
OUTPUT
PEDAL
PEDAL
PEDAL
POLARITY REVERSE
POLARITY REVERSE
POLARITY REVERSE
180°
INPUT
RETURN
PEDAL - A
PEDAL - B
PEDAL - A
PEDAL - B
BLEND
EXTC
OUTPUT
INPUT
SEND
SEND
RETURN
BLEND
EXTC
POLARITY 180°
PHASE
CANCELLATION
NORMAL
PHASE
NORMAL
PHASE
NORMAL
PHASE
Once you get the EXTC hooked up, you will find it to be loads of fun! All of a sudden, you
will be going back into the attic looking for that box of forgotten pedals, dusting them off and
plugging them in. Some will sound fantastic, others will sound bad in a good way. Who knows,
only those brave enough to enter blindly into these cold waters may live to tell the tale.
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