Crown Audio 800CSL service manual Output Device Emulation Protection Odep, Low Side LS

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Power Base-2 & 800CSL Amplifier Service Manual

Theory

the positive half, and about .5V across the bias resistor in the negative half. Q18 conduction (and thus bias) is adjustable.

A diode string prevents excessive charge build up within the high conduction output devices when off. Flyback diodes shunt back-EMF pulses from reactive loads to the power supply to protect output devices from dangerous reverse voltage levels. An output terminating circuit blocks RF on output lines from entering the amplifier through its output connectors.

Low Side (LS)

The Low Side (LS) operates quite differently. The power supply bridge rectifier is not ground refer- enced, nor is the secondary of the main transformer. In other words, the high voltage power supply floats with respect to ground, but ±Vcc remain constant with respect to each other. This allows the power supply to deliver +Vcc and -Vcc from the same bridge rectifier and filter as a total difference in potential, regardless of their voltages with respect to ground. The LS uses inverted feedback from the HS output to control the ground reference for the rails (±Vcc). Both LS quad- rants are arranged in a three-deep Darlington and are biased AB+B in the same manner as the HS.

When the amplifier output swings positive, the audio is fed to an op-amp stage where it is inverted. This inverted signal is delivered directly to the bases of the positive (NPN) and negative (PNP) LS predrivers. The negative drive forces the LS PNP devices on (NPN off). As the PNP devices conduct, Vce of the PNP Darlington drops. With LS device emitters tied to ground, -Vcc is pulled toward ground reference. Since the power supply is not ground referenced (and the total voltage from +Vcc to -Vcc is constant) +Vcc is forced higher above ground potential. This contin- ues until, at the positive amplifier output peak, -Vcc = 0V and +Vcc equals the total power supply potential with a positive polarity. If, for example, the power supply produced a total of 70V from rail to rail (±35VDC measured from ground with no signal), the amplifier output would reach a positive peak of +70V.

Conversely, during a negative swing of the HS output where HS PNP devices conduct, the op-amp would output a positive voltage forcing LS NPN devices to conduct. This would result in +Vcc swinging toward ground potential and -Vcc further from ground poten- tial. At the negative amplifier output peak, +Vcc = 0V and -Vcc equals the total power supply potential with

a negative polarity. Using the same example as above, a 70V supply would allow a negative output peak of - 70V. In summary, a power supply which produces a total of 70VDC rail to rail (or ±35VDC statically) is capable of producing 140V peak-to-peak at the ampli- fier output when the grounded bridge topology is used. The voltage used in this example are relatively close to the voltages of the PB-1/460CSL.

The total effect is to deliver a peak to peak voltage to the speaker load which is twice the voltage produced by the power supply. Benefits include full utilization of the power supply (it conducts current during both halves of the output signal; conventional designs require two power supplies per channel, one positive and one negative), and never exposing any output device to more than half of the peak to peak output voltage (which does occur in conventional designs).

Low side bias is established by a diode string which also shunts built up charges on the output devices. Bias is adjustable via potentiometer. Flyback diodes perform the same function as the HS flybacks. The output of the LS is tied directly to chassis ground via ground strap.

OUTPUT DEVICE EMULATION PROTECTION (ODEP)

To further protect the output stages, a specially devel- oped ODEP circuit is used. It produces a complex analog output signal. This signal is proportional to the always changing safe-operating-area margin of the output transistors. The ODEP signal controls the Volt- age Translator stage by removing drive that may exceed the safe-operating-area of the output stage.

ODEP senses output current by measuring the volt- age dropped across LS emitter resistors. LS NPN current (negative amplifier output) and +Vcc are sensed, then multiplied to obtain a signal proportional to output power. Positive and negative ODEP voltages are adjustable via two potentiometers. Across ±ODEP are a PTC and a thermal sense (current source). The PTC is essentially a cutoff switch that causes hard ODEP limiting if heatsink temperature exceeds a safe maximum, regardless of signal level. The thermal sense causes the differential between +ODEP and – ODEP to decrease as heatsink temperature increases. An increase in positive output signal output into a load will result in –ODEP voltage dropping; an increase in negative output voltage and current will cause +ODEP voltage to drop. A complex RC network between the

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Contents Power BASE-2& 800CSL Avis Table of Contents Scope WarrantyIntroduction Parts Mechanical SpecificationsPower PerformanceBLU Voltage ConversionFront END Operation FeaturesTheory OverviewVoltage Translators Error AmpHigh Side HS Grounded Bridge TopologyLow Side LS Output Device Emulation Protection OdepPositive Standard Initial Conditions Checkout ProceduresTest 2 Output Bias Adjustment Test 3 Odep Voltage AdjustmentTest 12 Output Power Test 4 AC Power DrawTest 5 Common Mode Rejection Test 7 Phase ResponseTest 17 Turn on Transients Test 16 Signal to Noise RatioTest 14 Odep Limiting Test 15 LF ProtectionPost Testing Mechanical Non-Module Parts Chassis Front Assembly Output Assembly ONE PER ChannelBack Panel Assembly Main Chassis Assembly Main Modules Module InformationModule History Output ModulesQ42647-0 Output Module Parts List P10137-1 Board Q42717-1 Output Module MT/MA #2 for PB-2 Q42717-1 Output Module Parts List P10233-8 BoardQ42871-6 Output Module MT/MA TO-3P Driver for PB-2/ 800CSL Q42871-6 Output Module Parts List P10305-4 BoardQ42966-4 Output Module TO-3P Driver #2 for PB-2/ 800CSL Q42966-4 Output Module Parts List P10305-4 BoardQ43015-9 Output Module Parts List P10341-9 Board Q43203-1 Output Module Parts List P10397-1 Board Q42665-2 Main Module Original for PB-2 Q42665-2 Main Module Parts List D 6910-0 BoardNetwork Resistors IC’S SwitchesQ42683-5 Main Module #2 for PB-2 Q42683-5 Main Module Parts List D 6910-0 BoardZero OHM InterconnectsQ42818-7 Main Module 3rd Gain for PB-2/800CSL Q42818-7 Main Module Parts List D 7251-8 BoardDpdt Side Header 5 PIN Q43059-7 Main Module Parts List D 7993-5 Board Jumper UPA75

800CSL specifications

Crown Audio has long been a respected name in professional audio equipment, and the 800CSL amplifiers are a testament to their unwavering commitment to quality and performance. Designed for professional sound reinforcement applications, the Crown 800CSL offers an impressive blend of power, reliability, and versatility, making it a popular choice among audio engineers and event coordinators.

At the heart of the Crown 800CSL is its robust power output. This amplifier delivers an impressive 800 watts per channel at 4 ohms, ensuring that it can drive even the most demanding speakers with ease. It features a Class D design, which not only maximizes efficiency, allowing for more power with less heat generation, but also contributes to a lightweight chassis that is easy to transport and install. This makes the 800CSL a versatile option for both permanent installations and mobile events.

One of the key technologies employed in the Crown 800CSL is its comprehensive built-in protection circuitry. This includes advanced short circuit protection, over-temperature protection, and current limiting. Such features ensure that the amplifier operates reliably in challenging conditions, reducing the risk of damage to both the amplifier and the connected speakers. The inclusion of a low-frequency filter further enhances performance, providing clean, powerful bass without distortion.

The Crown 800CSL also offers a range of connectivity options, including XLR and ΒΌ-inch inputs, making it compatible with a wide variety of audio sources. This flexibility, combined with user-friendly front panel controls, allows audio professionals to set up and adjust the system quickly and efficiently.

Additionally, the amplifier features a robust and compact design with a lightweight aluminum chassis. This not only contributes to its portability but also aids in heat dissipation, further enhancing performance during prolonged use. The included handles on the chassis make it easy to transport the unit between gigs, while its durable components ensure longevity.

In summary, the Crown Audio 800CSL stands out for its power, efficiency, and reliability. From its Class D amplification technology to its comprehensive protection features, this amplifier is designed to meet the needs of professionals in the audio industry. Whether for concerts, events, or installations, the 800CSL is poised to deliver exceptional sound quality and performance, making it a valuable addition to any audio toolkit.
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