Crown 460CSL service manual Voltage Translators, Error Amp

Page 9

Power Base-1 & 460CSL Amplifier Service Manual

Theory

tivity is achieved by controlling the ratio of feedback to

Voltage Translators

input resistance. The Sensitivity Switch sets the input

A voltage divider network splits the Error Signal (ES)

impedance to this stage and varies the gain such that

into positive and negative drive signals for the bal-

the overall amplifier gain is 26 dB, or is adjusted

anced voltage translator stage. These offset reference

appropriately for 0.775V or 1.4V input to attain rated

voltages drive the input to the Voltage Translator

output. Note that earlier models (before main modules

transistors. A nested NFb loop from the output of the

built with D 7911-7 board) did not support the 1.4V

amplifier mixes with the inverted signal riding on the

sensitivity.

offset references. This negative feedback fixes gain at

 

the offset reference points (and the output of the Error

Error Amp

Amp) at a factor of -25.2 with respect to the amplifier

The inverted output from the VGS is fed to the non-

output. The Voltage Translators are arranged in a

inverting input of the Error Amp op-amp stage through

common base configuration for non-inverting voltage

an AC coupling capacitor and input resistor. Amplifier

gain with equal gain. They shift the audio from the

output is fed back via the negative feedback (NFb)

±15V reference to VCC reference. Their outputs drive

loop resistor. The ratio of feedback resistor to input

their respective LVA.

resistor fixes gain from the Error Amp input to the

 

output of the amplifier at 26 dB. Diodes prevent

Also tied into the Voltage Translator inputs are ODEP

overdriving the Error Amp. Because the Error Amp

limiting transistors and control/protection transistors.

amplifies the difference between input and output

The ODEP transistors steal drive as dictated by the

signals, any difference in the two waveforms will

ODEP circuitry (discussed later). The control/protec-

produce a near open loop gain condition which in turn

tion transistors act as switches to totally shunt audio to

results in high peak output voltage. The output of the

ground during the turn-on delay, or during a DC/LF or

Error Amp, called the Error Signal (ES) drives the

Fault protective action.

Voltage Translators.

 

VOLTAGE AMPLIFICATION

 

 

 

 

Last Voltage Amplifiers (LVAs)

 

 

 

 

 

The Voltage Translator stage channels the signal to

The Voltage Translator stage separates the output of

 

the Last Voltage Amplifiers (LVA's) in a balanced

the Error Amp into balanced positive and negative

 

configuration. The +LVA and -LVA, with their push-pull

drive voltages for the Last Voltage Amplifiers (LVAs),

 

effect through the Bias Servo, drive the fully comple-

translating the signal from ground referenced ±15V to

 

mentary output stage. The LVAs are configured as

±Vcc reference. LVAs provide the main voltage ampli-

 

common emitter amplifiers. This configuration pro-

fication and drive the High Side output stages. Gain

 

vides sufficient voltage gain and inverts the audio. The

from Voltage Translator input to amplifier output is a

 

polarity inversion is necessary to avoid an overall

factor of 25.2.

 

 

 

 

 

polarity inversion from input jack to output jack, and it

 

BGS

VGS

Error

+15V

 

 

 

 

 

Voltage

+VCC

 

 

 

 

 

 

 

Translators

 

Audio

+

+

Amp

Divider

 

 

 

 

 

 

NPN Outputs (+HS)

+

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Q100

Q121

Q101

Q105

 

 

 

 

 

 

 

 

 

Inputs

 

 

 

Voltage

 

 

 

 

 

Q102

-

-

-

 

 

 

Q103

 

 

PNP Outputs (-HS)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Q122

 

Q110

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

- +

 

Mute

 

 

-VCC

 

 

 

 

-15V

ODEP

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

NFb Loop

 

LVA's

 

 

Figure 1. Typical Amplifier Front End and Voltage Amplification Stages.

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Contents Power BASE-1& 460CSL Avis Table of Contents Warranty IntroductionScope Parts Power SpecificationsPerformance MechanicalBLU Voltage ConversionTheory FeaturesOverview Front END OperationVoltage Translators Error AmpHigh Side HS Grounded Bridge TopologyLow Side LS Output Device Emulation Protection OdepPositive Test 2 Output Bias Adjustment Checkout ProceduresTest 3 Odep Voltage Adjustment Standard Initial ConditionsTest 5 Common Mode Rejection Test 4 AC Power DrawTest 7 Phase Response Test 12 Output PowerPost Testing Test 16 Signal to Noise RatioTest 14 Odep Limiting Test 15 LF ProtectionCheckout Procedures Mechanical Non-Module Parts Output Assembly ONE PER Channel Back Panel AssemblyChassis Front Assembly Main Chassis Assembly Module History Module InformationOutput Modules Main ModulesQ42576-1 Output Module Parts List P10137-1 Board Q42661-1 Output Module 4 Resistor #2 for PB-1 Q42661-1 Output Module Parts List P10137-1 BoardQ42718-9 Output Module 4 Resistor #3 for PB-1 Q42718-9 Output Module Parts List P10233-8 BoardQ42885-6 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 Q42552A0 Main Module Parts List D 6304B2 Board Network ResistorsQ42552A0 Main Module Original for PB-1 IC’S SwitchesQ42664-5 Main Module Parts List D 6910-0 Board UPA75 PNP Q42682-7 Main Module #2 for PB-1 Q42682-7 Main Module Parts List D 6910-0 BoardTrim POT InterconnectsBoard Mounts U1, U2 Q42776-7 Main Module 3rd Gain for PB-1 Q42776-7 Main Module Parts List D 7251-8 BoardDpdt 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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