A
musical
instrument
such as
an
electric
guitar
or
electronic
keyboard
uses a
High
Impedance,
Unbalanced
output.
This is
designed
to
operate
effectively
up to 15
or 20
feet
without
picking
up hum
and
electrical
or radio
interference.
If you
have a
short
distance
from the
instrument
to your
mixer,
or you
are
operating
in a
very
interference
free
room,
you
might be
able to
plug the
instrument
directly
into a
Line
Level
input on
the
mixer
using an
instrument
cable
with 1/4
inch
phone
connectors
on each
end.
This
cable
must be
a
shielded
instrument
cable.
Don't
try to
use an
unshielded
speaker
cable.
Converting
the
Instrument
Signal:
For
permanent
installations
or
greater
distances
to the
mixer,
you need
to
convert
the
instrument
signal
from
High
Impedance
Unbalanced
Line
level to
Low
Impedance
Balanced
Microphone
level.
This can
be
accomplished
in one
of two
ways.
The most
often
seen
method
is using
a Direct
Interface
Box (DI
Box).
The
instrument
is
connected
to the
DI box
using a
standard
instrument
cable
with 1/4
inch
phone
connectors
on each
end. The
DI box
is then
connected
to a
microphone
jack
using a
standard
microphone
cable.
By
converting
the
signal,
you
greatly
reduce
the
possibility
of
interference
pick up
and make
the
instrument
look
like a
microphone
to your
mixer.
If you
want to
also
feed
sound to
a local
guitar
or
keyboard
amplifier,
some DI
boxes
have a
second
Unbalanced
output
which
will do
this.
Direct
Interface
Boxes:
A
couple
of
popular
Direct
Boxes are
the DB25
(passive)
and ADB2
(active).
Both
have
unbalanced
instrument
inputs
and
unbalanced
line
level
and
balanced mic
level
outputs.
Both
have
attenuation
and
ground
lift
switches.
The
ADB2,
active
box has
a very
broad
frequency
response
from 1
Hz
through
50 KHz,
while
the DB25
covers
50 Hz
through
15 KHz.
For
instruments
with
very low
or high
harmonics
such as
organ
foot
pedals,
the
active
box
might be
the
better
choice.
It does
however
require
phantom
power.
The
Direct
Interface
Cable:
Another
method
is to
use a
Direct
Interface
Cable.
This
performs
the same
function
as the
DI box
except
it
accomplishes
it using
one
component
instead
of
three.
The
DI25
Direct
interface
cable
is a 25
foot
cable
with a
mic
connector
on one
end and
a 1/4
inch
phone
connector
with
built in
transformer
on the
other
end. It
plugs
into a
keyboard,
guitar,
VCR etc.
and
converts
from the
high
impedance
unbalanced
signal
out of
the
instrument
to low
impedance
balanced
mic
level.
The
other
end
plugs
into a
standard
microphone
jack.
This
cable
enables
you to
plug any
instrument
into any
microphone
jack
without
picking
up hum
and
electrical
interference.
The
DI25
Cable
saves
you
money
and set
up time
since
there is
one
component
instead
of
three.
It is
also
more
immune
to
interference
since it
converts
the
signal
right at
the
instrument
output
instead
of at
the box
end of
the
instrument
cable.
If you
want to
use a
local
amplifier
for the
instrument,
you can
connect
from the
instrument
to the
amplifier,
then
from the
amplifier
"pre-amp"
or
"line"
output
to your
microphone
jack
using
the DI25
cable.
