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Left
INPUT 1
Right
Select #1
TRIM
Left
TRIM
INPUTS 2 & 3
Select #2
Right
Left
TRIM
Select #4
INPUTS 4, 5 & 6
Right
Fig 6.1.1
INPUT 1
The input is routed through a pair of half normalled TRS jacks and into a
differential amplifier. The TRIM varies the gain of the differential amplifier so
ensuring maximum headroom at all gain settings. The output of this amplifier is fed
via CMOS switches onto the mix buss.
INPUT 2 & 3
Inputs 2 and 3 are similar to Input 1 without the insert jacks.
INPUT 4, 5 & 6
These inputs are similar to Inputs 1-3 but are unbalanced.
The CMOS switches are controlled by the input select logic block. This consists of
six set-reset latches. Pressing a select button sets its latch and sends a reset
signal to all the other latches.
Signals on the mix buss are summed by two virtual earth amplifiers. These feed
the TAPE RECORD output. The mixed signal also feeds the BALANCE pot,
MONO and DIM switches.
OUTPUT 1 & 2 are relay switched. These relays are controlled by the OUTPUT on-
off switches and the power on-off circuitry. The output amplifiers are configured as
ground compensated, balanced impedance.
All inputs and outputs have RFI filtering.
MIX
•
L
R
Tape Send L
•
•
•
Mix amp
•
BALANCE
•
Tape Send R
•
•
Mix amp
•
•
Select
•
#1
•
Select
#2
•
Select
Input
•
#3
Select
•
Select
#4
•
•
Select
#5
•
Select
#6
Power
~
•
on-off
Delay
SPX20 block diagram showing main signal paths
6.0 CIRCUIT DESCRIPTION
L
R
•
•
MONO
DIM
LEVEL 1
•
•
•
•
1
LEVEL 2
2
•
3
4
5
VOLUME
6
On-Off #1
•
OUTPUT 1 ON-OFF
OUTPUT 2 ON-OFF
Page 13
Left
OUTPUT 1
On-Off #1
Right
Left
OUTPUT 2
On-Off #2
Right
HEADPHONES
On-Off #2
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