User Guide

26
PFL Mix & Output Module [Diagram XL88_3]
The channel module pfl lines are individually selected by the eight push buttons
with associated Led indicators that are located on this pcb [B2702]. The pushes
keep the select lines high [+15V] in the off state and at 0V in the selected (on)
state.
The select lines are fed to the modules via the ribbon cable buss connected to ST1.
The pfl audio mix buss enters the module via ST1 pin 10. It is buffered by IC1a
and the signal fed to IC2 the balancing network for the Pfl output which appears
on three terminal pins H [hot] C [cold] and G [gnd],the output is protected
from excess voltage by the diode bridge D9-12, and set for maximum common
mode rejection at 100Hz by VR1 [typically 85dB].
The three terminal pins are connected by screened cable to the rear panel mounted
XLR PFL Output socket pins 1 [G], 2 [C] and 3 [H].
The facility to link together the pfl mix buss of more than one XL88 mixer exists
on the pfl board. Two terminal pins are fitted 0V and Sig. These give direct pfl
buss input. If this is to be used, the 3 pin Pfl output xlr should be replaced with
a 5 pin xlr, the pfl output should be connected to pins 1, 2 and 3 as above and
the pfl buss input should be connect to pins 4 [0V] and 5 [SIG].
Switch LED powering.
The status LEDs are powered by the current source based around Q1. The order
for the chain is from Q1 to the pfl select switches 1 thro 8 and then to the negative
rail.
Module power connection.
The mixer power supply connects to ST2 on this module. From here it is distrib-
uted to all other modules by the main ribbon cable. 40 pin headers are used for the
channel modules with a 20 pin header on the pfl module. The first eight ways are
used for this purpose as follows:-
PIN 1 & 2 - Input/output gnd.
PIN 3 & 4 - Psu 0 Volts.
PIN 5 & 6 - Psu -15 Volts.
PIN 7 & 8 - Psu +15 Volts.