ARP 2600 - Page 110

109
7.
ADJUST
THE
VCO-1
TRIMMER
LABELLED
"FREQ
CAL"
UNTIL
PITCH
IS
SLIGHTLY
FLAT
OF A-1
1
0Hz,
TWO
OCTAVES BELOW
A-440Hz.
(A-440
is
the
first
A
above
middle
C.)
8. Repeat
steps 3 through
7,
substituting VCO-2
for
VCO-1.
9. Repeat
steps 3 through
7,
substituting VCO-3
for
VCO-1
.
6.112 VCO
TRACKING ADJUSTMENTS.
1
.
All
sliders should
be
at
their MINIMUM (down or
left)
position.
2.
Insert
a
dummy
plug
into
the KBD
CV
jack input
to
VCO-3.
3.
Advance the
VCO-3
input to
the Filter,
the
Filter input
to
the
Mixer, and
the
two
Speaker Volume
controls
to
a
com-
fortable level.
4. Set
the
VCO-3
INITIAL FREQUENCY to
100Hz
and the
FINE TUNE
to center.
5.
Open partially
the
VCO-2
input
to the Filter
and,
while
holding down the lowest note
on
the
keyboard,
tune
VCO-2
to unison
with
VCO-3
by
"zero-beating"
the
two
oscillators.
(In using the FINE
TUNE
slider
for
precise
tuning
of this
sort,
the best
method
is to
press
in
one
direction with your
thumb at
the base of the
slider, resting on the
panel,
while
the
index
finger holds the
top
of the
slider
back
in
the
other
direction,
as
in the
drawing.)
6.
Holding down
the
C
three
octaves
above
the
lowest
note
on
the
keyboard,
ADJUST
THE
TRIMMER
LABELLED
"1V/OCT"
UNTIL
VCO-2
EXACTLY
ZERO-BEATS WITH
VCO-3's EIGHTH
(which is
three octaves
above the
funda-
mental)
HARMONIC.
This
will'be
made
easier
if
you
adjust
the
Filter
inputs so
that
VCO-3
is
considerably
louder than
VCO-2.
7.
Repeat
steps
5
and
6
substituting VCO-1
for VCO-2.
8.
Remove the dummy
plug
from
the
KBD CV
input
to VCO-3
9.
While
holding
down
the
lowest note
on
the
keyboard,
tune
FCO's 2
and
3
to unison
by
zero-beating
them.