An audio power amplifier includes a first and a second amplification unit, each including a switching voltage amplifier, an output filter, a current compensator, an inner current feedback loop feeding a measurement of current measured at the output inductor back to a summing input of the current compensator, a voltage compensator coupled to the summing input of the current compensator, and an outer voltage feedback loop. A controlled signal path provides the output of the voltage compensator of the first amplification unit to the current compensator of the second amplification unit. The first and second amplification units are operable with separate loads, in parallel driving a common load, or across a bridge-tied-load. A second pair of amplification units may be added and operated together with the first pair to drive a single speaker with a parallel pair of amplifiers on each side of a bridge-tied-load.
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28. An audio power amplifier comprising:
a four-quadrant power supply having a synchronous output rectifier;
a first, a second, a third and a fourth amplification unit, each amplification unit comprising:
a switching voltage amplifier having a command signal input and an amplified signal output; and
control electronics providing signal inputs to each of the amplification units and controlling the first, second, third and fourth amplification units such that:
the first and second amplification units are operable with separate loads, in parallel driving a common load, or across a bridge-tied-load,
the third and fourth amplification units are operable with separate loads, in parallel driving a common load, or across a bridge-tied-load, and
all four of the amplification units are operable together with the first and second units in parallel driving a first side of a bridge-tied-load, and the third and fourth units in parallel driving a second side of the bridge-tied-load.
1. An audio power amplifier comprising:
a four-quadrant power supply having a synchronous output rectifier;
a first amplification unit and a second amplification unit, each amplification unit comprising:
a switching voltage amplifier having a command signal input and an amplified signal output,
an output filter between the amplified signal output and a load terminal,
a current compensator with a current-compensated command signal output coupled to the command signal input of the switching voltage amplifier,
an inner current feedback loop feeding a measurement of current measured at the output filter back to a summing input of the current compensator,
a voltage compensator with a voltage-compensated command signal output coupled to the summing input of the current compensator, and
an outer voltage feedback loop feeding voltage at the load terminal back to a summing input of the voltage compensator; and
control electronics providing signal inputs to the first and second amplification units and controlling the first and second amplification units such that the first and second amplification units are operable with separate loads, in parallel driving a common load, or across a bridge-tied-load.
13. An audio power amplifier comprising:
a first, a second, a third, and a fourth amplification unit, each amplification unit comprising:
a switching voltage amplifier having a command signal input and an amplified signal output,
an output filter between the amplified signal output and a load terminal,
a current compensator with a current-compensated command signal output coupled to the command signal input of the switching voltage amplifier,
an inner current feedback loop feeding a measurement of current measured at the output filter back to a summing input of the current compensator,
a voltage compensator with a voltage-compensated command signal output coupled to the summing input of the current compensator, and
an outer voltage feedback loop feeding voltage at the load terminal back to a summing input of the voltage compensator; and
control electronics providing signal inputs to the first and second amplification units and controlling the first and second amplification units such that the first and second amplification units are operable with separate loads, in parallel driving a common load, or across a bridge-tied-load,
the control electronics further providing signal inputs to the third and fourth amplification units such that the third and fourth amplification units are operable with separate loads, in parallel driving a common load, or across a bridge-tied-load, and
all four of the amplification units are operable together with the first and second amplification units in parallel driving a first side of a bridge-tied-load, and the third and fourth amplification units in parallel driving a second side of the bridge-tied-load.
20. An audio power amplifier comprising:
a first, a second, a third, and a fourth amplification unit, each amplification unit comprising:
a switching voltage amplifier having a command signal input and an amplified signal output,
an output filter between the amplified signal output and a load terminal,
a current compensator with a current-compensated command signal output coupled to the command signal input of the switching voltage amplifier,
an inner current feedback loop feeding a measurement of current measured at the output filter back to a summing input of the current compensator,
a voltage compensator with a voltage-compensated command signal output coupled to the summing input of the current compensator, and
an outer voltage feedback loop feeding voltage at the load terminal back to a summing input of the voltage compensator;
a four-quadrant power supply having a synchronous output rectifier, the power supply providing power to the first, second, third and fourth amplification units; and
control electronics providing signal inputs to the first and second amplification units and controlling the first and second amplification units such that the first and second amplification units are operable with separate loads, in parallel driving a common load, or across a bridge-tied-load,
the control electronics further providing signal inputs to the third and fourth amplification units such that the third and fourth amplification units are operable with separate loads, in parallel driving a common load, or across a bridge-tied-load, and
all four of the amplification units are operable together with the first and second amplification units in parallel driving a first side of a bridge-tied- load, and the third and fourth amplification units in parallel driving a second side of the bridge-tied-load.
2. The audio power amplifier of
3. The audio power amplifier of
4. The audio power amplifier of
5. The audio power amplifier of
a third and a fourth amplification unit substantially identical to the first and second amplification units,
the control electronics further providing signal inputs to the third and fourth amplification units and controlling the third and fourth amplification units such that the third and fourth amplification units are operable with separate loads, in parallel driving a common load, or across a bridge-tied-load, and
all four of the amplification units are operable together with the first and second amplification units in parallel driving a first side of a bridge-tied-load, and the third and fourth amplification units in parallel driving a second side of the bridge-tied-load.
6. The audio power amplifier of
amplifying a first signal in each of the first and second amplification units and providing substantially identical amplified first signals on separate output terminals of the first amplification unit and the second amplification unit,
amplifying an inverse of the first signal in each of the third and fourth amplification units and providing substantially identical amplified inverted first signals on separate output terminals of the third amplification unit and the fourth amplification unit,
wherein the output terminals of the first and second amplification units are coupled to a first input of the load, and the output terminals of the third and fourth amplification units are coupled to a second input of the load.
7. The audio power amplifier of
8. The audio power amplifier of
a first controlled signal path from the voltage-compensated command signal output of the voltage compensator of the first amplification unit to the summing input of the current compensator of the second amplification unit,
the second amplification unit configured to use the voltage-compensated command signal of the first amplification unit as input to the current compensator of the second amplification unit in place of the voltage-compensated command signal of the second amplification unit when the first controlled signal path is activated.
9. The audio power amplifier of
10. The audio power amplifier of
11. The audio power amplifier of
12. The audio power amplifier of
14. The audio power amplifier of
amplifying a first signal in each of the first and second amplification units and providing substantially identical amplified first signals on separate output terminals of the first amplification unit and the second amplification unit,
amplifying an inverse of the first signal in each of the third and fourth amplification units and providing substantially identical amplified inverted first signals on separate output terminals of the third amplification unit and the fourth amplification unit,
wherein the output terminals of the first and second amplification units are coupled to a first input of the load, and the output terminals of the third and fourth amplification units are coupled to a second input of the load.
15. The audio power amplifier of
a first controlled signal path from the voltage-compensated command signal output of the voltage compensator of the first amplification unit to the summing input of the current compensator of the second amplification unit,
the second amplification unit configured to use the voltage-compensated command signal of the first amplification unit as input to the current compensator of the second amplification unit in place of the voltage-compensated command signal of the second amplification unit when the first controlled signal path is activated; and
a second controlled signal path from the voltage-compensated command signal output of the voltage compensator of the third amplification unit to the summing input of the current compensator of the fourth amplification unit,
the fourth amplification unit configured to use the voltage-compensated command signal of the third amplification unit as input to the current compensator of the fourth amplification unit in place of the voltage-compensated command signal of the fourth amplification unit when the second controlled signal path is activated.
16. The audio power amplifier of
17. The audio power amplifier of
18. The audio power amplifier of
19. The audio power amplifier of
21. The audio power amplifier of
amplifying a first signal in each of the first and second amplification units and providing substantially identical amplified first signals on separate output terminals of the first amplification unit and the second amplification unit,
amplifying an inverse of the first signal in each of the third and fourth amplification units and providing substantially identical amplified inverted first signals on separate output terminals of the third amplification unit and the fourth amplification unit,
wherein the output terminals of the first and second amplification units are coupled to a first input of the load, and the output terminals of the third and fourth amplification units are coupled to a second input of the load.
22. The audio power amplifier of
a first controlled signal path from the voltage-compensated command signal output of the voltage compensator of the first amplification unit to the summing input of the current compensator of the second amplification unit,
the second amplification unit configured to use the voltage-compensated command signal of the first amplification unit as input to the current compensator of the second amplification unit in place of the voltage-compensated command signal of the second amplification unit when the first controlled signal path is activated; and
a second controlled signal path from the voltage-compensated command signal output of the voltage compensator of the third amplification unit to the summing input of the current compensator of the fourth amplification unit,
the fourth amplification unit configured to use the voltage-compensated command signal of the third amplification unit as input to the current compensator of the fourth amplification unit in place of the voltage-compensated command signal of the fourth amplification unit when the second controlled signal path is activated.
23. The audio power amplifier of
24. The audio power amplifier of
25. The audio power amplifier of
26. The audio power amplifier of
27. The audio power amplifier of
29. The audio power amplifier of
amplifying a first signal in each of the first and second amplification units and providing substantially identical amplified first signals on separate output terminals of the first amplification unit and the second amplification unit,
amplifying an inverse of the first signal in each of the third and fourth amplification units and providing substantially identical amplified inverted first signals on separate output terminals of the third amplification unit and the fourth amplification unit,
wherein the output terminals of the first and second amplification units are coupled to a first input of the load, and the output terminals of the third and fourth amplification units are coupled to a second input of the load.
30. The audio power amplifier of
31. The audio power amplifier of
32. The audio power amplifier of
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This application is a continuation of U.S. patent application Ser. No. 13/160,806 filed on Jun. 15, 2011 and titled “Versatile Audio Power Amplifier,” which is a continuation of U.S. patent application Ser. No. 12/717,198 filed on Mar. 4, 2010 and titled “Versatile Audio Power Amplifier” (now U.S. Pat. No. 7,986,187), each of which are incorporated by reference in their entirety.
This disclosure relates to a versatile audio power amplifier.
Switching amplifiers, also called Class D amplifiers, amplify an input signal by modulating that signal into a series of pulses that drive a complementary pair of transistors operated in the switching mode. The transistors alternately couple positive and negative power sources to the output, which in total produce an amplified representation of the input signal.
In general, in some aspects, an audio power amplifier includes a first and a second amplification unit. Each amplification unit includes a switching voltage amplifier having a command signal input and an amplified signal output, an output filter between the amplified signal output and a load terminal, a current compensator with a current-compensated command signal output coupled to the command signal input of the voltage amplifier, an inner current feedback loop feeding a measurement of current measured at the output inductor back to a summing input of the current compensator, a voltage compensator with a voltage-compensated control signal output coupled to the summing input of the current compensator, and an outer voltage feedback loop feeding voltage at the load terminal back to a summing input of the voltage compensator. A first controlled signal path provides the voltage-compensated control signal output of the voltage compensator of the first amplification unit to the summing input of the current compensator of the second amplification unit. The second amplification unit uses the voltage-compensated control signal of the first amplification unit as input to the current compensator of the second amplification unit in place of the voltage-compensated command signal of the second amplification unit when the first controlled signal path is activated. Control electronics provide signal inputs to the first and second amplification units and control the first controlled signal path such that the first and second amplification units are operable with separate loads, in parallel driving a common load, or across a bridge-tied-load.
Implementations may include one or more of the following features. The first and second amplification units may be operable with separate loads by each amplifying separate signals and providing the amplified signals on their separate output terminals. The first and second amplification units may be operable in parallel driving a common load by each amplifying the same signal, provided from the first amplification unit to the second amplification unit via the first controlled signal path, and providing identical amplified signals on their separate output terminals, which are to be coupled to a common input terminal of the load. The first and second amplification units may be operable across a bridge-tied-load by amplifying a first signal in the first amplification unit and amplifying an inverted copy of the first signal in the second amplification unit, and providing their respective amplified signals on their separate output terminals, which are to be coupled to separate input terminals of the load.
A third and a fourth amplification unit identical to the first and second amplification units, and a second controlled signal path from the voltage-compensated control signal output of the voltage compensator of the third amplification unit to the summing input of the current compensator of the fourth amplification unit may be included, the control electronics further providing signal inputs to the third and fourth amplification units and controlling the second controlled signal path such that the third and fourth amplification units are operable with separate loads, in parallel driving a common load, or across a bridge-tied-load, and all four of the amplification units are operable together with the first and second units in parallel driving a first side of a bridge-tied-load, and the third and fourth units in parallel driving a second side of the bridge-tied-load.
The four amplification units may be operable together by amplifying a first signal in each of the first and second amplification units, provided from the first amplification unit to the second amplification unit via the first controlled signal path, and providing identical amplified first signals on the separate output terminals of the first amplification unit and the second amplification unit, amplifying an inverted copy of the first signal in each of the third and fourth amplification units, provided from the third amplification unit to the fourth amplification unit via the second controlled signal path, and providing identical amplified inverted first signals on the separate output terminals of the third amplification unit and the fourth amplification unit, the output terminals of the first and second amplification units are to be coupled to a first input of the load, and the output terminals of the third and fourth amplification units are to be coupled to a second input of the load.
The amplifier may use a four-quadrant power supply having a synchronous output rectifier. The synchronous output rectifier may include a MOSFET. The first controlled signal path may include a switch controlled by the control electronics. The switching voltage amplifiers may each include a modulator, a gate driver, a pair of transistors, and a pair of diodes coupled between the source and drain terminals of the transistors. The transistors may include MOSFETS, the diodes being intrinsic to the MOSFETS. The output filter may include an output inductor and the measured current may be the current through the output inductor.
In general, in some aspects, amplifying audio-frequency signals includes, in each of a first and a second amplification unit, amplifying a current-compensated command signal in a switching voltage amplifier to provide an amplified signal output, measuring current through an output filter between the amplified signal output of the voltage amplifier and a load terminal to produce a current measurement, feeding back the current measurement to a summing input of a current compensator via an inner current feedback loop, at the current compensator, comparing the current measurement to a voltage-compensated command signal and providing the current-compensated command signal to the voltage amplifier, feeding back voltage at a load terminal of the amplification unit to a summing input of a voltage compensator via an outer voltage feedback loop, and at the voltage compensator, comparing the feedback voltage to an input command signal and providing the voltage-compensated command signal to the summing input of the current compensator. A first controlled signal path from an output of the voltage compensator of the first amplification unit to the summing input of the current compensator of the second amplification unit is controlled to selectively provide the voltage-compensated command signal of the first amplification unit to the summing input of the second amplification unit in place of the voltage-compensated command signal of the second amplification unit. Signal inputs are provided to the first and second amplification units and the first controlled signal path is controlled to selectively operate the first and second amplification units with separate loads, in parallel driving a common load, or across a bridge-tied-load.
Advantages include comprehensive configurability with high efficiency. The amplifier can serve a wide variety of connection topologies, load impedances, and power levels without hardware modification. Being able to drive loudspeakers at a wide range of impedances from a single amplifier allows the amplifier to support a diverse range of audio system configurations without requiring a diverse set of amplifier products.
Other features and advantages will be apparent from the description and the claims.
Power amplifiers may be connected to their loads in a number of topologies, depending on the nature and intended use of the loads.
In
Finally, in
With a class D amplifier, management of current-sharing between two parallel amplifiers is more important than in linear, or class AB, amplifiers, because the dissipated power in a switching device is proportional to I2, rather than to I, as it is in a linear amplifier. Sharing current between two identical devices will decrease conduction loss by roughly a factor of two in the switching amplifier. The decrease will actually be a bit more than a factor of two because there are further gains due to the temperature coefficient of resistance of the FET—decreasing the current also decreases the temperature, which in turn decreases the intrinsic resistance of the device. If the current is not controlled, however, it is likely that one of the two devices will deliver substantially more current than the other, losing the benefits of parallel operation and possibly damaging the amplifiers.
To provide efficient current sharing in topologies, a feedback loop may be added to the amplifier. For example, as shown in
To allow current sharing when two of these unit cells 100 are connected in parallel, an inner current loop 130 is provided. The inner current loop 130 feeds back a measurement of output current, from a current sense 130a, to another summer 132 and current-loop compensator 134. The inner current loop controls the output current of the amplifier, so that two amplifiers operating in parallel will each provide half the total current; neither will attempt to deliver all the current and lose the advantages of parallel operation. In this configuration, the current loop around the core voltage amplifier turns the system into a current amplifier, and the outer voltage loop turns the entire unit cell 100 back into a voltage amplifier.
The inner current loop provides some additional advantages. The current loop naturally provides current limiting within the unit cell. That is, the feedback 130 to the current-loop compensator 134 prevents the command into the modulator 102 from causing a current gain in excess of the maximum current command from the voltage-loop compensator 116, even if the load is shorted. Additionally, because the inner current loop provides control, the voltage measurement used for the outer voltage loop can be moved outside the output filter, closer to the load (as shown). (An output filter typically imposes a 180° phase shift, around which a control loop could not be closed.) Moving the voltage loop to after the output filter allows the amplifier to support a greater variety of loads while the inner current loop maintains stability. The inner current loop 130 can also be used to provide pulse width error correction in the modulator 102, as described in U.S. patent application Ser. No. 12/717,224, titled “Reducing Pulse Error Distortion,” and filed the same day as this application, the entire contents of which are incorporated here by reference.
The summers 114 and 132 are not necessarily discrete components, but may be, for example, summing inputs of the compensators 116 and 134. The compensators preferably are built from standard circuit components, i.e., op-amps and associated circuitry. The current-sensing element 130a may be any standard current-sensing technology, such as discrete Hall-effect sensors. The output inductor 108 may be formed using planar windings on a printed circuit board, and part of the current sense is provided by a current sense winding integrated into the output inductor 108, as described in U.S. patent application Ser. No. 12/717,208, titled “Planar Amplifier Output Inductor with Current Sense,” and filed the same day as this application, the entire contents of which are incorporated here by reference. As explained in that patent application, forming the current-sense winding as part of the PCB windings of the output inductor advantageously shields the current-sense signal from noise within the inductor. The inductor's current-sensing winding indicates an AC component of the current, while a Hall-effect sensor may also be used to indicate the DC component of the current.
In some examples, these unit cells are combined in groups of 4. Each group has appropriate interconnections within the control system, allowing a single set of four unit cells to provide any of the topologies shown in
For independent half-bridge operation of multiple channels, each unit cell is connected to one loudspeaker as shown in
As shown in
As shown in
As shown in
In some embodiments, the control circuitry of each of the half-bridge unit cells is independent, such that when two cells are used in the BTL or parallel configuration, the other two may be used as independent half-bridges, in the same two-cell configuration as the first two cells, or in the other two-cell configuration. In some examples, pairs or all four of the amplifier stages (modulator and gate drive) are provided in a single integrated circuit package, such as the TDA8932 from NXP Semiconductors, in Eindhoven, The Netherlands, or the TAS5103 from Texas Instruments in Dallas, Tex., while the transistors, control loops, and output filters are added to complete the amplifiers and enable the configurability described above. In some examples, the control loops and cross-cell connections are included in the amplifier IC.
As shown in
For the two unit cells 100a and 100b being operated as independent half-bridges, a first switch 204a controls the signal path between the two unit cells 100a and 100b, for providing common current control when operating in parallel, as discussed above. In the example of
For BTL operation, an inverter 214 is available to couple an inverted copy of input signal “A” to the unit cell 100b, where the switch 212 would provide that signal rather than the input “B” used for half-bridge operation. This is the case in the second pair of unit cells 100c and 100d, where the switch 204b is open, and a switch 216 is coupling an inverter 218 to the input of unit cell 100d, providing an inverted copy of input “C”. Another inverter 220 and input switch 222 control the input to unit cell 100c, for use in parallel-bridged configurations, discussed below with reference to the second set of four unit cells. In
Unit cells 100e and 100f are shown configured for parallel operation. In this mode, the input switch 224 on unit cell 100f does not provide any signal input to the second unit cell, as the closed switch 204c provides the current command signal from inside the unit cell 100e to the current feedback loop comparator in unit cell 100f, skipping the voltage command input and voltage feedback loop comparator of unit cell 100f. In some configurations, the input of unit cell 100f is disconnected internally when used in parallel operation, so the input switch 224 may remain coupled to one of its inputs. The inverter 226 is available to provide an inverted version of input “E” for use in BTL mode. Unit cells 100g and 100h are also shown configured for parallel operation, and in particular, they are configured for use in a parallel-bridged mode with unit cells 100e and 100f. Switch 204d provides the current command signal to unit cell 100h from inside unit cell 100g, while switch 228 is open and inverter 230 is unused. At unit cell 100g, a switch 232 couples an inverted copy of input “E” from an inverter 234 to the input of unit cell 100g, so that the two sets of parallel half-bridges 100e/100f and 100g/100h receive E and −E, respectively, as inputs.
Although the switches, inverters, and signal sources are shown external to the control module 210, some or all of the switches and inverters may be integrated into the control module, and may be configured in hardware, firmware, or software, depending on the technology used. If the switches and inverters are integrated to the control module, the inputs A through H would also pass through the control module. The control module may be any suitable device, such as a programmed microprocessor, an application-specific integrated circuit, or a collection of discrete devices. The control module may also apply digital signal processing to the inputs A through H, in addition to the switching and inverting used to configure the amplifier topology. There may be a separate control module for each set of four unit cells. In some cases, the control module may be configured to use all eight unit cells in a cascading pattern of bridged and parallel groupings to deliver the entire capacity of the power supply to one loudspeaker (additional connections between amplifiers and/or signal paths would be needed, though these may all be provided by a suitable control module).
Such a configuration is capable of driving numerous configurations of loudspeakers. For example, an 4000 W amplifier system containing two groups of four unit cells, at 500 W each, can drive many different combinations of speakers, as shown in table 1 (with the actual wattage depending on the impedance of the particular loudspeakers used).
Unit 1
Unit 2
Unit 3
Unit 4
Unit 5
Unit 6
Unit 7
Unit 8
500 W
500 W
500 W
500 W
500 W
500 W
500 W
500 W
1000 W Parallel or
1000 W Parallel or
500 W
500 W
500 W
500 W
BTL
BTL
1000 W Parallel or
1000 W Parallel or
1000 W Parallel or
500 W
500 W
BTL
BTL
BTL
2000 W Parallel-Bridged
1000 W Parallel or
500 W
500 W
BTL
2000 W Parallel-Bridged
1000 W Parallel or
1000 W Parallel or
BTL
BTL
2000 W Parallel-Bridged
2000 W Parallel-Bridged
One or more of these groups of four unit cells are combined with an appropriate power supply, such as that described in co-pending U.S. patent application Ser. No. 12/717,216, titled “Power Supply Transient Response Improving,” and filed the same day as this application, the entire contents of which are incorporated here by reference. In some examples, an advantageous feature provided within the power supply is a synchronous output rectifier, which solves the ‘bus pumping’ problem generally associated with class D half-bridges, and supports efficient operation of the highly-configurable amplifier stages described above (the bus-pumping problem is explained for reference below). A schematic representation of this synchronous output rectifier 300 is shown in
At the voltage levels typically used in an audio power amplifier, e.g., +/−80V or higher on the secondary windings, the secondary side switches 314-320 in this topology would typically be simple rectifiers. Instead, MOSFETs are used with their intrinsic diodes to provide a synchronous rectifier. This allows power to flow in either direction at any of the three ports of this power converter (+400 V primary, +80 V secondary, −80 V secondary), providing for full four-quadrant operation, as explained in
At lower output voltages, when the voltage drop across the rectifiers becomes a significant source of inefficiency, synchronous rectifiers are in common use today. However, they are not commonly used at the high voltages of audio power amplifiers, as the efficiency increase is very marginal, and there are significant technical hurdles to overcome to make the MOSFETs robust with reverse current flow and parasitic diode recovery. Using the technique in the system described above allows energy flow from reactive loads back into the system to be evenly distributed between all of the storage capacitance in the system, and it also solves the bus pumping problem associated with half-bridge class D stages.
Bus pumping, also known as off-side charging or rail pumping, is explained with reference to
In the first state, as shown in
In the second state, as shown in
The expression for average current regenerated into the rail over a half sine wave is as follows:
where ‘p’ is average power out, ‘v’ is rail voltage, and ‘r’ is load resistance. For example, a 20 Hz sine wave into a 4Ω load, of sufficient amplitude to give 500 W average power output, in an amplifier with ±80 V rails, will regenerate an average of 3 A over a half cycle. With 10 000 μF of capacitance on that rail, the system will experience a bus pumping of 7.5 V, which is almost 10% of the nominal. By using synchronous rectification, lower capacitances can be used and the system will still experience significantly less perturbation. In one example, with the above-mentioned voltages, a system with only 3500 μF capacitance per channel per rail experienced significantly less pumping of the bus than that just described.
Other implementations are within the scope of the following claims and other claims to which the applicant may be entitled.
Pearce, Daniel Scott, Nussbaum, Michael, Sheen, Timothy
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