Crown 460CSL service manual Grounded Bridge Topology, High Side HS

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Power Base-1 & 460CSL Amplifier Service Manual

Theory

allows the NFb loop to control Error Amp gain by

 

The output of the +LVA drives the base of predriver

feeding back to its non-inverting input (with its polarity

 

device. Together, the predriver and driver form the

opposite to the output of the VGS). With the added

 

first two parts of the three-deep Darlington and are

voltage swing provided by the LVAs, the signal then

 

biased class AB. They provide output drive through

gains current amplification through the Darlington

 

the bias resistor, bypassing the output devices, at

emitter-follower output stage.

 

levels below about 100mW. An RLC network between

GROUNDED BRIDGE TOPOLOGY

 

the predriver and driver provide phase shift compen-

 

sation and limit driver base current to safe levels.

Figure 2 is a simplified example of the grounded

 

Output devices are biased class B, just below cutoff.

bridge output topology. It consists of four quadrants

 

At about 100mW output they switch on to conduct high

of three deep Darlington (composite) emitter-follower

 

current to the load. Together with predriver and driver,

stages per channel: one NPN and one PNP on the

 

the output device provide an overall class AB+B

High Side of the bridge (driving the load), and one

 

output.

NPN and one PNP on the Low Side of the bridge

 

The negative half of the HS is almost identical to the

(controlling the ground reference for the rails). The

 

output stages are biased to operate class AB+B for

 

positive half, except that the devices are PNP. One

ultra low distortion in the signal zero-crossing region

 

difference is that the PNP bias resistor is slighter

and high efficiency.

 

greater in value so that PNP output devices run closer

 

 

to the cutoff level under static (no signal) conditions.

High Side (HS)

 

This is because PNP devices require greater drive

The High Side (HS) of the bridge operates much like

 

current.

a conventional bipolar push-pull output configuration.

 

HS bias is regulated by Q18, the Bias Servo. Q18 is a

As the input drive voltage becomes more positive, the

 

HS NPN conducts and delivers positive voltage to the

 

Vbe multiplier which maintains approximately 3.3V

load. Eventually the NPN devices reach full conduc-

 

Vce under static conditions. The positive and negative

tion and +Vcc is across the load. At this time the HS

 

halves of the HS output are in parallel with this 3.3V.

PNP is biased off. When the drive signal is negative

 

With a full base-emitter on voltage drop across

going, the HS PNP conducts to deliver -Vcc to the load

 

predrivers and drivers, the balance of voltage results

and the HS NPN stage is off.

 

in approximately .35V drop across the bias resistors in

 

+

 

+Vcc (Positive Rail)

 

Input

 

 

signal

Load

 

 

 

 

(speaker)

 

 

Inverting Op-amp

 

HIGH SIDE

-Vcc (Negative Rail)

LOW SIDE

-

Figure 2. Crown Patented Grounded Bridge Topology

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Contents Power BASE-1& 460CSL Avis Table of Contents Introduction WarrantyScope Parts Performance SpecificationsPower MechanicalVoltage Conversion BLUOverview FeaturesTheory Front END OperationError Amp Voltage TranslatorsGrounded Bridge Topology High Side HSOutput Device Emulation Protection Odep Low Side LSPositive Test 3 Odep Voltage Adjustment Checkout ProceduresTest 2 Output Bias Adjustment Standard Initial ConditionsTest 7 Phase Response Test 4 AC Power DrawTest 5 Common Mode Rejection Test 12 Output PowerTest 14 Odep Limiting Test 16 Signal to Noise RatioPost Testing Test 15 LF ProtectionCheckout Procedures Mechanical Non-Module Parts Back Panel Assembly Output Assembly ONE PER ChannelChassis Front Assembly Main Chassis Assembly Output Modules Module InformationModule History Main ModulesQ42576-1 Output Module Parts List P10137-1 Board Q42661-1 Output Module Parts List P10137-1 Board Q42661-1 Output Module 4 Resistor #2 for PB-1Q42718-9 Output Module Parts List P10233-8 Board Q42718-9 Output Module 4 Resistor #3 for PB-1Q42885-6 Output Module Parts List P10305-4 Board Q42967-2 Output Module Parts List P10341-9 Board Q43200-7 Output Module Parts List P10397-1 Board Network Resistors Q42552A0 Main Module Parts List D 6304B2 BoardQ42552A0 Main Module Original for PB-1 Switches IC’SQ42664-5 Main Module Parts List D 6910-0 Board UPA75 PNP Q42682-7 Main Module Parts List D 6910-0 Board Q42682-7 Main Module #2 for PB-1Interconnects Trim POTBoard Mounts U1, U2 Q42776-7 Main Module Parts List D 7251-8 Board Q42776-7 Main Module 3rd Gain for PB-1Dpdt Side Header 5 PIN Q42953-2 Main Module Parts List D 7251-8 Board UPA75 Misc Q43060-5 Main Module Parts List D 7993-5 Board Jumper 7325-1 Ground Lift 7960-5 Sensitivity 6781-6 Stereo/Mono

460CSL specifications

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