Z111B
and its associated components form
an active equivalent of a series resonant LCR
circuit. This has an impedance minimum 5.4k
at around 80.
The digital pots
Z108D
and
Z108A
control the
bass
and
treble
respectively,
this
accomplished by moving the wiper connected
to
the
frequency-sensitive
impedance
between to non inverting and inverting
terminals of
Z112A
, effectively changing the
ratio of feedback boost and feed forward
attenuation of the circuit at the desired
frequencies, thus providing a EQ gain control
that is on a logarithmic scale, with the use of
a linear pot.
Z112B
provides the 6dB of gain necessary to
bring the nominal level of signal back to unity
C116
and
C117
remove the 2.5VDC offset
from the output to prevent click and bangs
when the tone control are activated.
Z108
is controlled by a simple 3-wire serial
interface from the microprocessor. Each of
the digital lines has it’s own ground return
these are terminated at the GND pin of the
chip
to
minimize
any
electromagnetic
interference.
Volume control
Z107
is a VSDVC electronic volume control
IC. It works in conjunction with external op-
amp
Z117a/b
by varying the feed-forward and
feedback resistors in an inverting gain
configuration, the volume control is driven by
3-wire data from the H8 micro on the display
board – if the control receives no data it will
remain in Audio mute mode.
Relay RLY100 shunts the output of the Op-
amps to ground at switch on – power down
and when switching between inputs.
Audio output stages.
The Audio
output
stage contains the
buffered, un-buffered and balanced outputs
as well as the headphone driver.
The audio signal from the preamp PCB
enters the board on
CON100
and the direct
signal goes straight to the output via the mute
relays
RlY100A
and
RLY101B
. A buffered
version of the signal is created by
IC100
and
IC101
.
IC100 and IC101 are op-amps
configured
as
unity
gain
non-inverting
buffers.
The C30 also has a Balance XLR output
stage that drives into the balanced line
drivers
IC103
and
IC104
. These line divers
create a transformer-less balanced output.
Headphone Output.
The selected audio output signal is driven
into the headphone driver
IC102
; this signal
then passes through
CON101
and
CON102
to the headphone socket
SKT101
. The mute
signal passes through the switch contacts in
the headphone socket so when headphones
are inserted the main outputs are relay
muted.
Please note:
this means that if the
headphone sockets control contacts are
faulty
or
damaged
the
unit
will
be
permanently stuck in audio mute mode.
RC5 remote code assignment change.
The C30 has the ability to switch between
RC5 system code 16* and 19, we can
achieve this by pressing and holding the
Phono/Aux – CD and AV – DVD buttons
simultaneously the display will show.
RC5 System Code
16*
We can toggle the system code using the
rotary encoder.
Summary of Contents for C30, P35
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