Crown PIP-102 Service Manual Page 12
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MA-3600VZ Service Manual
Theory of Operation 3-2
130366-1 Rev. A
©2000 Crown International, Inc.
an AC coupling capacitor and input resistor. Amplifi er
output is fed back via the negative feedback (NFb)
loop resistor. The ratio of feedback resistor to input
resistor fi xes gain from the Error Amp input to the
output of the amplifier at 26 dB. Diodes prevent
overdriving the Error Amp. Because the Error Amp
amplifi es the difference between input and output
signals, any difference in the two waveforms will
produce a near open loop gain condition which in
turn results in high peak output voltage. The output
of the Error Amp, called the Error Signal (ES) drives
the Voltage Translators.
3.4 Voltage Amplifi cation
The Voltage Translator stage separates the output of
the Error Amp into balanced positive and negative
drive voltages for the Last Voltage Amplifi ers (LVAs),
translating the signal from ground referenced ±15V
to ±Vcc reference. LVAs provide the main voltage
amplifi cation and drive the High Side output stages.
Gain from Voltage Translator input to amplifi er output
is a factor of 25.2.
3.4.1 Voltage Translators
A voltage divider network splits the Error Signal
(ES) into positive and negative drive signals for
the balanced voltage translator stage. These offset
reference voltages drive the input to the Voltage
Translator transistors. A nested NFb loop from
the output of the amplifi er mixes with the inverted
signal riding on the offset references. This negative
feedback fi xes gain at the offset reference points (and
the output of the Error Amp) at a factor of -25.2 with
respect to the amplifi er output. The Voltage Translators
are arranged in a common base confi guration for
non-inverting voltage gain with equal gain. They shift
the audio from the ±15V reference to VCC reference.
Their outputs drive their respective LVA.
Also tied into the Voltage Translator inputs are
ODEP limiting transistors and control/protection
transistors. The ODEP transistors steal drive as
dictated by the ODEP circuitry (discussed later). The
control/protection transistors act as switches to totally
shunt audio to ground during the turn-on delay, or
during a DC/LF or Fault protective action.
3.4.2 Last Voltage Amplifi ers (LVAs)
The Voltage Translator stage channels the signal
to the Last Voltage Amplifi ers (LVA’s) in a balanced
confi guration. The +LVA and -LVA, with their push-
pull effect through the Bias Servo, drive the fully
complementary output stage. The LVAs are confi gured
as common emitter amplifiers. This configuration
provides suffi cient voltage gain and inverts the audio.
The polarity inversion is necessary to avoid an overall
polarity inversion from input jack to output jack, and
it allows the NFb loop to control Error Amp gain by
feeding back to its non-inverting input (with its polarity
opposite to the output of the VGS). With the added
voltage swing provided by the LVAs, the signal then
gains current amplifi cation through the Darlington
emitter-follower output stage.
3.5 Grounded Bridge Topology
Figure 3.2 is a simplifi ed example of the grounded
bridge output topology. It consists of four quadrants
of three deep Darlington (composite) emitter-follower
stages per channel: one NPN and one PNP on the
High Side of the bridge (driving the load), and one
NPN and one PNP on the Low Side of the bridge
(controlling the ground reference for the rails). The
output stages are biased to operate class AB+B for
ultra low distortion in the signal zero-crossing region
and high effi ciency.
+
-
+
-
+
-
BGS VGS Error
Amp
Audio
Inputs
Voltage Divider
NFb Loo
p
+
-
ODEP
Mute
+15V
-15V
+VCC
-VCC
NPN Outputs (+HS)
PNP Outputs (-HS)
Q100
Q103
Q121
Q122
Q101
Q102
Q105
Q110
Voltage
Translators
LVA’s
Figure 3.1 Typical Amplifi er Front End and Voltage Amplifi cation Stages.
- SERVICE MANUAL 1
- Revision History 3
- MA-3600VZ Service Manual 4
- 130366-1 Rev. A 4
- Table of Contents 5
- 1 Introduction 7
- Introduction 1-2 8
- 2 Specifi cations 9
- 2.7 Construction 10
- 2.5 Input/Output 10
- 2.6 Protection 10
- 3 Theory of Operation 11
- 3.4 Voltage Amplifi cation 12
- 3.5 Grounded Bridge Topology 12
- 3.5.2 Low Side (LS) 13
- 3.5.1 High Side (HS) 13
- 3.7 VZ Power 14
- 3.7.2 The VZ supply 15
- 3.7.3 VZ Switch Control 15
- 1/4" PHONE 16
- 4 Maintenance 17
- 4.3.5 Test 4: AC Power Draw 18
- 4.3.7 Test 6: Voltage Gain 18
- 4.3.8 Test 7: Phase Response 18
- 5.1 General Information 21
- 5.3 Mechanical Parts 21
- Crown Customer Service 21
- 5.3.1 Top Chassis Assembly 23
- 5.3.3 Front Assembly 27
- 5.3.4 Back Panel Assembly 29
- 5.3.7 Fan Assembly 34
- 5.3.8 Heatsink Assembly 35
- 5.3.9 Standard PIP Assembly 37
- 5.4 Circuit Board Parts 39
- Parts 5-29 49
- PWA #Q43387-2 Component Map 49
- Parts 5-30 50
- Capacitors 51
- Resistor Networks 51
- Transistors 51
- Resistors 52
- Switches 53
- Integrated Circuits 53
- Miscellaneous 53
- Parts 5-53 73
- PWA #Q43382-3 Component Map 73
- Parts 5-54 74
- PWA #Q43323-7 Component Map 95
- Parts 5-75 95
- Parts 5-76 96
- 6 Schematic Diagrams 103
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