Premier Service Center Certification: Advanced Amplifiers
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Thank you for taking the time to participate in the QSC Premier Service Center Certification program.
To become a QSC Premier Service Center, you must pass four tests built off the online training material courses. This certification program is intended to allow your Service Center become fully capable and knowledgeable in servicing QSC products professionally and reliably.
This third test will cover the more advanced amplifeir technologies, like Class H and Class D. Good luck!
- 1.
What specific type of Class H output circuitry do QSC amplifiers use? Mark all that apply.
- A.
1-tier
- B.
2-tier
- C.
3-tier
- D.
4-tier
Correct Answer(s)
B. 2-tier
C. 3-tier
D. 4-tierExplanation
QSC amplifiers use 2-tier, 3-tier, and 4-tier Class H output circuitry. Class H amplifiers are designed to improve efficiency by using multiple power supply rails. The tiers refer to the number of voltage levels used in the amplifier's output stage. In a 2-tier configuration, there are two voltage levels, while a 3-tier configuration has three voltage levels, and a 4-tier configuration has four voltage levels. By using multiple tiers, QSC amplifiers can optimize power usage and reduce distortion, resulting in improved performance and efficiency.Rate this question:
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- 2.
Does QSC offer any power amplifiers with Class D output circuitry technology?
- A.
Yes
- B.
No
Correct Answer
A. YesExplanation
QSC does offer power amplifiers with Class D output circuitry technology.Rate this question:
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- 3.
How many bipolar supply rails (count POS & NEG rails as 1) does a Class AB output circuitry use?
- A.
1
- B.
2
- C.
3
- D.
4
Correct Answer
A. 1Explanation
A Class AB output circuitry typically uses only one bipolar supply rail. This means that there is one positive (+) rail and one negative (-) rail, which are counted as a single rail. This type of circuitry is commonly used in audio amplifiers and other applications where high power and low distortion are required. By using a single bipolar supply rail, the circuit can efficiently amplify both positive and negative signals without requiring additional power supplies.Rate this question:
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- 4.
How many bipolar supply rails (count POS & NEG rails as 1) does a Class H output circuitry use?
- A.
2 or more
- B.
0
- C.
1
- D.
2 positive rails and 1 negative rail
Correct Answer
A. 2 or moreExplanation
A Class H output circuitry uses 2 or more bipolar supply rails. This means that it requires at least two supply rails, with one being positive and the other being negative. The use of bipolar supply rails allows for the amplification and output of audio signals with both positive and negative voltage swings, providing more flexibility and dynamic range in the audio output.Rate this question:
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- 5.
What type of circuit is the step driver (the circuit that turns the MOSFET switch off and on) in a Class H amplifier?
- A.
Comparator
- B.
Resistor network
- C.
H-Bridge
- D.
Stair circuit
Correct Answer
A. ComparatorExplanation
The step driver in a Class H amplifier is a comparator. A comparator is a circuit that compares two voltage inputs and outputs a digital signal based on the comparison. In the case of a Class H amplifier, the comparator is responsible for turning the MOSFET switch on and off to control the amplification of the audio signal. It compares the input voltage with a reference voltage and generates the appropriate control signal to switch the MOSFET.Rate this question:
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- 6.
What is the primary purpose of the MOSFET in a Class H amplifier?
- A.
To switch the output to a higher voltage rail.
- B.
To flip the voltage of the rail from positive to negative.
- C.
To allow for higher currents.
- D.
To put moss on your fet.
Correct Answer
A. To switch the output to a higher voltage rail.Explanation
The primary purpose of the MOSFET in a Class H amplifier is to switch the output to a higher voltage rail. This is achieved by controlling the flow of current through the MOSFET, which allows the amplifier to efficiently amplify the input signal to a higher voltage level. By switching the output to a higher voltage rail, the MOSFET helps to increase the overall power output of the amplifier.Rate this question:
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- 7.
What are some of the advantages of a Class H output circuitry? Mark all that apply.
- A.
More efficient
- B.
Reduced current consumption
- C.
More components
- D.
Easy to troubleshoot
Correct Answer(s)
A. More efficient
B. Reduced current consumptionExplanation
A Class H output circuitry offers advantages such as being more efficient and having reduced current consumption. This means that it can deliver power more effectively and consume less energy, resulting in improved overall performance and energy savings. However, the statement "More components" is not correct as Class H circuitry typically involves fewer components compared to other circuit designs. Additionally, the statement "Easy to troubleshoot" is not applicable as the ease of troubleshooting depends on various factors and cannot be solely attributed to the use of Class H circuitry.Rate this question:
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- 8.
How many pairs of step drivers (if you count POS & NEG as 1 pair) should a 2-tier Class H amplifier have?
- A.
0
- B.
1
- C.
2
- D.
3
Correct Answer
B. 1Explanation
A 2-tier Class H amplifier should have 1 pair of step drivers. This is because a 2-tier amplifier consists of two stages, and each stage requires a pair of step drivers to control the voltage supply. Therefore, there should be a total of 1 pair of step drivers in a 2-tier Class H amplifier.Rate this question:
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- 9.
What are some of the disadvantages of a Class H output circuitry? Mark all that apply.
- A.
More components
- B.
Increase in heat
- C.
More current consumption
- D.
Easy to troubleshoot
Correct Answer
A. More componentsExplanation
A Class H output circuitry has the disadvantage of requiring more components compared to other types of output circuitry. This means that the circuitry becomes more complex and potentially more expensive to manufacture and maintain.Rate this question:
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- 10.
In a class H amplifier, the positive step driver circuitry differs from the negative step driver in which way?
- A.
The positive step driver has a bootstrap power supply.
- B.
The positive step driver has a comparator and the negative step driver does not.
- C.
The positive step driver is in a good mood and the negative step driver is in a bad mood.
- D.
Both step drivers are similar in every way, just changed for positive or negative voltage.
Correct Answer
A. The positive step driver has a bootstrap power supply.Explanation
The positive step driver in a class H amplifier differs from the negative step driver by having a bootstrap power supply. This means that the positive step driver utilizes a circuit that allows the voltage to be boosted or "bootstrapped" to a higher level, which can improve the efficiency and performance of the amplifier. In contrast, the negative step driver does not have this feature.Rate this question:
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- 11.
The comparator in a step driver of a Class H amplifier compares what voltages?
- A.
Trigger and Reference
- B.
CH1 output and CH2 output
- C.
Output and Trigger
- D.
Positive and negative references
Correct Answer
A. Trigger and ReferenceExplanation
The comparator in a step driver of a Class H amplifier compares the trigger and reference voltages. The trigger voltage is the input signal that initiates the switching action, while the reference voltage is the threshold level that the trigger voltage is compared against. When the trigger voltage exceeds the reference voltage, the comparator triggers the switching action in the amplifier.Rate this question:
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- 12.
What is QSC's most widely used switch-mode power supply platform called?
- A.
PLC
- B.
PFC
- C.
PLX
- D.
PLD
Correct Answer
A. PLCExplanation
QSC's most widely used switch-mode power supply platform is called "PLC."Rate this question:
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- 13.
Which QSC amplifiers were developed with the PLC switch-mode power supply platform? Mark all that apply.
- A.
PLX
- B.
DCA
- C.
Powerlight 2
- D.
RMX
Correct Answer(s)
A. PLX
B. DCA
C. Powerlight 2Explanation
The QSC amplifiers that were developed with the PLC switch-mode power supply platform are PLX, DCA, and Powerlight 2.Rate this question:
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- 14.
In the PLC platform's switching power supply circuit, how is input AC energy rectified to DC?
- A.
Bridge rectifier
- B.
Line filter
- C.
DSP chip
- D.
Torodial power transformer
Correct Answer
A. Bridge rectifierExplanation
In the PLC platform's switching power supply circuit, the input AC energy is rectified to DC using a bridge rectifier. A bridge rectifier is a circuit that converts alternating current (AC) to direct current (DC). It consists of four diodes arranged in a bridge configuration. The diodes allow the current to flow in only one direction, effectively converting the AC input into a pulsating DC output. This rectified DC output is then used to power the various components of the PLC platform.Rate this question:
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- 15.
In the AC Line Filter circuit of QSC's switch mode power supply, what type of fuse is used?
- A.
Slow Blow (should not blow at short high current bursts)
- B.
Fast blow (should blow immediately when drawing high current)
- C.
500mA
- D.
Any fuse rated for 25 A
Correct Answer
A. Slow Blow (should not blow at short high current bursts)Explanation
In the AC Line Filter circuit of QSC's switch mode power supply, a slow blow fuse is used. This type of fuse is designed to withstand short high current bursts without blowing immediately. It has a delayed response to high current, allowing it to handle temporary surges without interrupting the circuit. This is important in switch mode power supplies where there can be sudden changes in current flow. Using a fast blow fuse would result in frequent blowing and interruption of the power supply. The specific current rating of the fuse is not mentioned in the question.Rate this question:
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- 16.
In QSC's switch-mode PLC platform, at what frequency do the power supply IGBTs switch on and off?
- A.
110 kHz
- B.
10 Hz
- C.
1 kHz
- D.
1 MHz
Correct Answer
A. 110 kHzExplanation
The power supply IGBTs in QSC's switch-mode PLC platform switch on and off at a frequency of 110 kHz.Rate this question:
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- 17.
What does the "I" in IGBT stand for?
- A.
Insulated
- B.
Inductive
- C.
Current (amps)
- D.
Inrush
Correct Answer
A. InsulatedExplanation
The "I" in IGBT stands for "Insulated." IGBT stands for Insulated Gate Bipolar Transistor, which is a type of semiconductor device used for power control and switching applications. The term "Insulated" refers to the fact that the gate of the IGBT is electrically isolated from the rest of the device, allowing for better control and protection against voltage spikes.Rate this question:
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- 18.
In the schematic below of a power supply in the PLC platform, what is the purpose of IC U19?
- A.
A controller IC that generates alternating signals for the gate driver IC.
- B.
Maintains the voltage supply (16V and 5V) for the power supply.
- C.
A gate driver IC that tells the IGBTs when to turn off and on.
- D.
An IC that monitors that output circuitry and cut off to protect the power supply.
Correct Answer
A. A controller IC that generates alternating signals for the gate driver IC.Explanation
IC U19 is a controller IC that generates alternating signals for the gate driver IC. This means that it is responsible for controlling the timing and frequency of the signals that tell the IGBTs when to turn off and on. By generating these alternating signals, IC U19 ensures that the power supply operates efficiently and effectively.Rate this question:
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- 19.
In the schematic below of a power supply in the PLC platform, what is the purpose of IC U18?
- A.
A driver IC that provides valid gate drive pulse trains to the IGBTs.
- B.
Maintains the voltage supply (16V and 5V) for the power supply.
- C.
An IC that monitors that output circuitry and cut off to protect the power supply.
- D.
An IC that makes giga-joules of energy, enough to power a Delorian.
Correct Answer
A. A driver IC that provides valid gate drive pulse trains to the IGBTs.Explanation
IC U18 is a driver IC that provides valid gate drive pulse trains to the IGBTs. This means that it controls the timing and amplitude of the signals that are sent to the IGBTs, which are insulated-gate bipolar transistors. The IGBTs are responsible for switching the high voltage power supply on and off, and the driver IC ensures that the signals are accurate and reliable.Rate this question:
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- 20.
What is the one of the purposes of the housekeeping supply circuit in the PLC platform?
- A.
To provide the operating voltages for components within the power supply.
- B.
To monitor all speaker output voltages.
- C.
To provide timing for the gate driver circuit.
- D.
To clean the power supply of any dirt.
Correct Answer
A. To provide the operating voltages for components within the power supply.Explanation
The purpose of the housekeeping supply circuit in the PLC platform is to provide the operating voltages for components within the power supply. This circuit ensures that all the necessary components receive the correct voltage for their operation, ensuring the proper functioning of the power supply. It is responsible for supplying power to various components such as relays, sensors, and other electrical devices within the power supply system.Rate this question:
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- 21.
In the PLC platform of amplifiers, what type of protect circuits exist in the power supply? Mark all that apply.
- A.
AC Loss
- B.
Undervoltage
- C.
Overcurrent
- D.
DC Fault
Correct Answer(s)
A. AC Loss
B. Undervoltage
C. Overcurrent
D. DC FaultExplanation
In the PLC platform of amplifiers, there are several types of protect circuits that exist in the power supply. These include AC Loss, which protects against the loss of AC power supply; Undervoltage, which protects against voltage levels below the acceptable range; Overcurrent, which protects against excessive current flow; and DC Fault, which protects against faults in the DC power supply. These protect circuits help ensure the proper functioning and safety of the amplifier system.Rate this question:
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- 22.
In the schematic below of a power supply in the PLC platform, what voltages does IC U13 pins 8 and 9 compare?
- A.
The bridge rectifier input voltage to detect loss of AC
- B.
The low voltage operating supplies.
- C.
The secondary voltage supply rails.
- D.
The voltage of the sync pin.
Correct Answer
A. The bridge rectifier input voltage to detect loss of ACExplanation
IC U13 pins 8 and 9 compare the bridge rectifier input voltage to detect loss of AC.Rate this question:
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- 23.
In the PLC platform of amplifiers, how does the power supply protect from overcurrent?
- A.
By measuring the average current draw and reducing the load on the power supply.
- B.
The housekeeping supply completley cuts off the main operating voltages, turning of the amplifier.
- C.
By detecting the reduction of input AC near the line filter.
- D.
By increasing the bias current to increase the secondary supply rails.
Correct Answer
A. By measuring the average current draw and reducing the load on the power supply.Explanation
The power supply in the PLC platform of amplifiers protects from overcurrent by measuring the average current draw and reducing the load on the power supply. This means that when the current draw exceeds a certain threshold, the power supply automatically adjusts the load to prevent any damage or failure. By monitoring and regulating the current draw, the power supply ensures the safe and efficient operation of the amplifiers.Rate this question:
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- 24.
The switch-mode power supply in the PLX2-04 models and GX7 are simplified versions of what?
- A.
The PLC platform of amplifiers.
- B.
The MD module.
- C.
The RMX Series amplifiers.
- D.
Class H amplifiers.
Correct Answer
A. The PLC platform of amplifiers.Explanation
The switch-mode power supply in the PLX2-04 models and GX7 are simplified versions of the PLC platform of amplifiers. This means that the power supply in these models has been simplified and designed based on the PLC platform, which is a type of amplifier platform.Rate this question:
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- 25.
In a Class D amplifier, what type of signal drives the switching transistors?
- A.
Pulse Width Modulated (PWM)
- B.
Trigger Referenced Comparator
- C.
Low frequency square wave
- D.
High frequency modulation (HFM)
Correct Answer
A. Pulse Width Modulated (PWM)Explanation
In a Class D amplifier, the switching transistors are driven by a Pulse Width Modulated (PWM) signal. This means that the amplitude of the signal remains constant, but the width of the pulses varies according to the input audio signal. This allows for efficient power conversion and high fidelity audio reproduction. The PWM signal is generated by comparing the input audio signal with a high frequency carrier signal and adjusting the width of the pulses accordingly.Rate this question:
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- 26.
In a Class D amplifier, what smooths the PWM pulse train back into an audio signal?
- A.
Low-pass reconstruction filter
- B.
An inductive circuit
- C.
High-Frequency filter
- D.
Driver transistors
Correct Answer
A. Low-pass reconstruction filterExplanation
A low-pass reconstruction filter is used in a Class D amplifier to smooth the PWM (Pulse Width Modulation) pulse train back into an audio signal. This filter allows only the lower frequency components of the signal to pass through, while attenuating the higher frequency components. By doing so, it removes the high-frequency switching noise of the PWM and reconstructs a clean audio signal that can be amplified and reproduced by the speaker.Rate this question:
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- 27.
In a Class D amplifier, why is the power dissipation so low during higher signal levels in comparison with Class A, B, AB, and H?
- A.
The output transistors are either fully on or fully off.
- B.
The output transistors are always on at a low level.
- C.
The output transistors are special ones meant for Class D.
- D.
The output transistors are so efficient that it puts nuclear power to shame.
Correct Answer
A. The output transistors are either fully on or fully off.Explanation
In a Class D amplifier, the power dissipation is low during higher signal levels because the output transistors are either fully on or fully off. This means that they are not in the linear region where they would dissipate significant power. Instead, they switch rapidly between these two states, resulting in very little power loss. This switching behavior allows Class D amplifiers to achieve high efficiency and minimize power dissipation, making them more efficient than Class A, B, AB, and H amplifiers.Rate this question:
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- 28.
Switching frequencies of Class D technology should be at least how many times faster than the highest audio frequency?
- A.
10x
- B.
2x
- C.
100x
- D.
250x
Correct Answer
A. 10xExplanation
In Class D technology, the switching frequency refers to how quickly the audio signal is converted into a digital waveform. The switching frequency needs to be at least 10 times faster than the highest audio frequency to accurately reproduce the audio signal. This is because the switching frequency determines the resolution and fidelity of the digital waveform, ensuring that all the nuances and details of the audio are captured and reproduced faithfully.Rate this question:
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- 29.
What are some of the problems of Class D technology? Mark all that apply.
- A.
Rail noise and voltage fluctuations affecting signal.
- B.
Dead time between positive and negative pulses
- C.
High frequencies like 100 kHz too fast for today's technology
- D.
Gain potentiometers not designed for switching amplifiers.
Correct Answer(s)
A. Rail noise and voltage fluctuations affecting signal.
B. Dead time between positive and negative pulsesExplanation
Class D technology refers to a type of amplifier that uses pulse width modulation (PWM) to deliver high power audio signals efficiently. One of the problems with Class D technology is that rail noise and voltage fluctuations can affect the quality of the signal being amplified. This can result in distortion or other unwanted artifacts in the audio output. Another problem is the dead time between positive and negative pulses, which can cause distortion or audible artifacts in the audio signal. Therefore, the correct answers are "Rail noise and voltage fluctuations affecting signal" and "Dead time between positive and negative pulses".Rate this question:
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- 30.
In the PL380 video orientation by Pat Quilter, how many relays click on the PL380 before the amplifier comes out of muting and is ready to go?
- A.
2
- B.
1
- C.
3
- D.
4
Correct Answer
A. 2Explanation
In the PL380 video orientation by Pat Quilter, there are two relays that click on the PL380 before the amplifier comes out of muting and is ready to go.Rate this question:
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- 31.
In the PL380 video orientation by Pat Quilter, what lies under the largest heatsink?
- A.
Class D output devices and auxiliary devices
- B.
Swtiching IGBTs
- C.
Secondary supply diodes
- D.
A cute and fuzzy dust bunny.
Correct Answer
A. Class D output devices and auxiliary devicesExplanation
The correct answer is Class D output devices and auxiliary devices. In the PL380 video orientation by Pat Quilter, the largest heatsink is covering these components. Class D output devices are responsible for amplifying the audio signal, while auxiliary devices provide additional support and functionality to the amplifier. These components generate heat during operation, which is why they are placed under the largest heatsink to dissipate the heat effectively and prevent overheating.Rate this question:
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Nov 15, 2023Quiz Edited by
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Aug 16, 2012Quiz Created by
Patrick Heyn
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