Front End Theory; Balanced Gain Stage; Variable Gain Stage; Error Amp - Crown Macro-Tech MA-5002VZ Service Manual

MA-5002VZ Service Manual
ing to case, and case to heatsink under both static and
dynamic conditions.
The output of the positive ODEP amplifier drives +ODEP
test point pin 11. It also drives U114A and U114B which
in turn drive – LH and +LL respectively. The output of
the negative ODEP amplifier drives the ODEP indica-
tion circuitry and – ODEP test point pin 9. Negative ODEP
also drives U114C and U114D which in turn drive +LH
and – LL respectively.
Also entering the U114 comparator networks are the
PWR (power relay engage), PWRLOSS (brown-out), and
FAULT (any protection which shuts down the amplifier)
signals via blocking diodes. If any of these signals drop
low, the feed to the LS bias and Voltage Translator drive
will be shut down via ±LL and ±LH. This action mutes
all audio in the event of a dramatic failure.

4.5 Front End Theory

Figure 4.5 explodes the front-end portion of the overall
block diagram. Once again, only channel 1 will be dis-
cussed in detail.
Input to the amplifier is only via a PIP module. The stan-
dard module shipped with the MA-5002VZ is the PIP2-
FXQ. Whether this, or any other module is used, the
amplifier senses a balanced input from the installed
module.
4-8 Circuit Theory
Figure 4.5 Front End Circuitry Block Diagram

4.5.1 Balanced Gain Stage

The Balanced Gain Stage (BGS) amplifier U100A con-
verts the input audio from a balanced configuration to
single-ended with (electrical) unity gain. The compres-
sion device is essentially a resistive shunt across the
balanced BGS input. The BGS drives the Variable Gain
Stage and provides information to the compressor con-
trol circuit and to the PIP connector.

4.5.2 Variable Gain Stage

The Variable Gain Stage (U100B) taps signal from the
wiper of the front panel level control (R120). Gain of the
front-end is set by the gain of this stage. The sensitivity
switch (S100, located on the rear panel) selects the
amount of gain in this stage. Overall amplifier sensitivity
may be set for 26 dB fixed gain (about 5.1Vrms), 1.4V,
or 0.775V. Since overall amplifier gain after this stage is
26 dB, this stage will have a fixed gain of 0 dB (26 dB
setting), about +12 dB (1.4V setting), or about +16 dB
(0.775V setting). The output of this stage drives the Er-
ror Amp.

4.5.3 Error Amp

The Error Amp (U105) input comes from the Variable
Gain Stage with or without Loudspeaker Offset Integra-
tion (LOI), and is summed with amplifier output in a nega-
tive feedback (NFb) configuration. Output of the Error
Amp drives the Voltage Translators and provides error
130446-1 Rev. A
©2000 Crown International, Inc.