3.4.3 - Channel Board
The actual generation of sound is performed by the Channel
board. Each of the 12 channels
on
it can create different arbitrary
sounds,
all of which
get
mixed together into two audio outputs.
These outputs are sent to
an
external amplifier and speakers via the
Audio board.
As
shown
in
the drawing, K250 Channel board (figure 3.9), the
Channel board
has several subsections of circuitry. The block
on
the
right hand side of the board is labeled CGP/Channel interface. The
section of the circuitry controls the flow of sound samples
in
an
orderly manner from the CGP to each of the 12 channels
on
the
Channel board. Each channel must receive its sound samples
in
exact
synchronizim with the channel timers located
on
the CPU board.
Since the K250 is a variable sampling rate instrument, each channel
may
be
playing out a sound at a different sample rate. There are two
sets of signals which go from the
CPU to the Channel board one
labeled FSAMP and the other labeled FALIAS. There are 12 FSAMP
signals, one for each channel and 12 FALIAS Signals, one for each
channel. These 24 signals come over the long flat ribbon cable from
the
CPU
board
to
the Channel board directly.
These two sets of
Signals are
generated
by the 24
programmable timers located
on
the
CPU
board. The clock rate for
each
FSAMP signal is precisely the sampling rate of that particular
channel. The
CGP
is
designed to deliver samples just
as
fast
as
the
Channel board can call for them for each of its channels. Therefore,
this section of circuitry could be thought of as a section which
trottles the flow of samples to each channel. The middle section of
the board is actually where the 12 identical channels reside.
All
channels are identical expect channel 12. Channel 12 varies
slightly from the other
11
in
one respect. Some of Channel 12's
circuitry is used for the sampling function.
The output of each of the 12 channels
is
then ·fed into a stereo
mixer section
on
the left hand side of the Channel board where the
12
channel~
are mixed into 2 channels. Driver amplifiers
in
this
section of circuitry amplify the left and right signals and feed them
to
the output connector which goes to the Audio board.
KUl'Z'!'lell 250 Service Manual, Chapter 3
3-
26
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