Multi channel input module (optional)
In
troduction
The multi input module an optional expansion
board that allows the existing Amp/Pre-amp
to become part of a surround system when
driven by a DVD/SACD player with Analogue
surround outputs.
The board has two sets of 7.1 input (8
channels) these are labelled as MCH1 and
MCH2 and accept Left, Right, Centre, Left
surround, Right surround, Left Back, Right
back audio Information.
All input channel levels can be trimmed levels
to allow for system balancing.
Put very simply this is an eight-channel
preamplifier.
Power supply
The board is powered from the +/- 15v supply
on the existing pre-amp board on board
regulators REG100 and REG101 regulate
these rails down to –5v and +5v respectively.
The digital sections of the circuit are powered
by a single +5v rail this is isolated from the
main 5v rail via inductor L100.
Capacitors C100, C101 and C105, C107 act
as bulk charge stores to prevent current
surges from affecting the main pre-amp stage
power supply stages.
Micro Processor
The micro controller operates from a
4 Mhz
crystal and is in control of all of the board’s
function via its input/output ports.
The micro controller is reset on power up via
R/C network R101 and C120. The micro
controller stays in reset condition for
approximately
500ms
this allows the host
micro controller (H8 Z1 on display board) to
initialize and for the power supplies to settle.
The Host micro communicates with the
onboard micro via CON 101. Three lines are
used for communication these are seen on
the circuit diagram as PB0, receive from
ExpBrd and Transmit to ExpBrd.
When the host is communicating with the
onboard micro controller PB0 will be driven
low, otherwise the Data sent will be ignored.
Input switching
The input allow for the signal routing of the
eight channels from either of the inputs these
are
MCH1
and
MCH2
, select lines
S1-S2-S3
are used to select each bank of inputs this
inputs stage utilizes 6 x 74HCT4053
multiplexers you will notice that IC204 and
I
C205
only utilize the
S1
and
S2
select
channels as this input switch only deals with
two channels (Back left and Back right).
Please note: The software will only allow one
set of inputs to be selected at any one time.
The outputs of the input multiplexers drive
into a group of 8 line drive Op-Amps
(IC300-IC307) these are configured two pole
integrating D.C servo before reaching the
Volume control stages.
Volume control
Volume control is performed by two channel
Burr-Brown PGA2310
volume control chips.
The gain is under micro control with steps of
0.5dB.
All volume control chips share
Data
,
Clock
and
Mute
control but have Chip select lines
that are grouped in the following way Front
Right, Front Left, Centre and Sub share the
same select line, and the remaining channels
share a chip select line (Surround right and
Left, Back right and Left). The volume of
each channel can be controlled individually
“trimmed”.
If a loud clicking is heard on a individual
channel whilst adjusting the volume it is
probably the input stage that is at fault and
not the volume control chip itself, the input
stage should prevent D.C levels form
entering the volume control.
To Next Page
Loading...
Need help?
General
