This contains the power amplifier electronics for the Left (L), Right (R),
Surround Back Left (SBL) and Surround Back Right (SBR) channels. It also
contains housekeeping logic for the amplifier protection system and power
drive circuits for the protection relays and cooling fans.
The power amplifiers are essentially identical to those in L125, except that the
lifter circuits are only shared between pairs of power amplifiers (L and SBL, R
and SBR respectively) rather than all three channels in L125. They receive
their raw DC power voltages from L125 via CON100.
Please refer to the
description of the Centre Channel (C) power amplifier (in L125) for a detailed
understanding of the circuitry of the power amplifiers in L129.
CON102 carries the L, R, SBL and SBR output signals to the speaker board
L124. It also de24V DC power and logic level switching signals to the 4
speaker relays on L124. NB - the ground returns shown on CON102 do not
carry L129’s main speaker currents back to the star point (which is located on
L125) but are merely used for the L, R, SBL and SBR amplifiers’ optional
extra Boucherot networks located on L124.
Note that it is L129 which communicates with the rest of the receiver, via two
ribbon cables connected to CON101 and CON 103. CON 101 receives 7 line
level input signals, and low voltage supplies (+12V, -12V and +5V) from L117.
CON101 also inputs the speaker relay mute signals for L124. CON103
supports temperature and DC offset monitoring for L125 and L129, plus a fan
drive signal, sent to and from the system microprocessor on L122, via L121.
The heatsink temperature monitors on L129 are IC800 and IC900; these are
located between the relevant pairs of lifter power MOSFETs.
TR102 provides n24V power to the output relays on L124, via the
unreg30V supply on L125. The 27V zener diode DZ102 prevents
excessive voltage being applied to the relays in the event of high mains
voltages.
REG 101 is not normally used as links CON109 and CON110 are omitted in
production. It pr5V for the on board logic and temperature sensors if
no +5V line is present (e.g. during development testing).
TR1003A/B and TR1001 together make a fan driver with a DC gain of 10, so it
can be triggered with a 3V3 microprocessor signal. Power comes from the
unregVlo supply (30V). The fans are two 12V DC units
connected in series fed from CON107 and CON108.
IC1000 is a triple 3-input NAND gate. To switch on (i.e. unmute) the speaker
relays, all 3 inputs on IC1000B (for LSB and RSB channels) and/or IC1000C
(for the other 5 channels) must be high. The 3 inputs come from:
(a) the AC present detector based around TR1002 and IC1000A,
(b) the ERR_NEG and ERR_POS detector, based around TR1004A/B, which
detects excessive DC offsets on any one or more of the 7 power amplifier
channels and (c) the ~MUTE_SB and ~MUTE_REST lines under the control
of the system microprocessor.
L129AY – Power Amp lower