Arcam-P1000-pwr-sm维修电路原理图.pdf

DiVA Service Manual P1000 Amplifier Issue 1.0 ARCAMARCAM Bringing music & movies to lifeBringing music & movies to life RadioFans.CN 收音机爱 好者资料库 Arcam P-1000 Amplifier Board functions and operation The power amplifiers in the P-1000 are of class H design and use a three rail power supply for high operating efficiency. These amplifier boards are field replaceable and the unit can be safely operated with one or more boards out of the unit. The operating descriptions below are divided into three groups. The input and signal control section. The amplifier section and the power switching section. Signal net name references as they appear in the schematic are designated here in bold type. The line level audio path of the P-1000 very simple and short. Unbalanced audio sources are buffered by U6-A and summed with the balanced input from U1-A. The signal then passes through the gain set stage of U6-B and then on to the AMP-IN amplifier drive. The AMP-IN signal is also contoured by U2-A and on to the power switching section via the COMM output. The gain switch S1 works by changing the local feedback around U6-B and has three settings. The “A” gain position provides an overall gain of 31.5 dB and is compatible with other Arcam amplifiers. The “B” setting is for use in THX compliant systems and the low gain “C” position can be used to lower the overall system noise level in installations where the speakers are very close to the listener. Also at the input of the gain set stage are the mute transistor Q1 and the resistive element of the clipping eliminator circuit. When the P-1000 is turned on, the global mute signal at the MUTE input of U3-A is low. This forces its output to +12V which activates the mute transistor Q1 as well as the clipping eliminator circuit through D15. The FLT_OUT from the emitter follower Q24 and also goes high. Q1 then shunts the audio to ground and R11 goes to a low resistance state. The FLT_OUT passes on out to the channel status display board. When the global mute cycle finishes and the output from U3-B goes low, Q1 turns off and passes the audio signal immediately but the resistive element R11 has a slow release time which allows the audio output to ramp up in a controlled manner. The local mute circuit of U3-B also has two other inputs. The thermal shutdown circuit of U2-B and R22 monitor the heatsink temperature of the amplifier. If the HS temperature exceeds approximately 95 Deg C, the output of U2-B goes high and toggles the local mute circuit on. Because of the hysteresis around U2-B, the thermal protection will remain active until the amplifier has cooled down approximately 20 Deg below the trip point. The second input is the PROT line from the amplifier. This is a fast acting input which goes to a low impedance state if a short circuit is detected at the amplifier output. The clipping eliminator circuit has two inputs. The AMPOUT monitors the amplifier output signal and the OPA-OUT signal from the output of U1-B. The OPA-OUT line is inside the overall amplifier feedback loop and is very sensitive to any differences between the input and output signals in the audio path. If the unit is driven into clipping the difference signal from these two lines is amplified and used to drive the CLM5000 LDR. This causes the resistance of R11 to decrease and work as part of a voltage divider against R85 or R5. The effect of this is to reduce the signal level going into the amplifier thereby reducing the output clipping to a very low value. Typically this circuit will hold the THD to less than 1% with 10dB of overdrive at the input. RadioFans.CN 收音机爱 好者资料库 Arcam P-1000 Amplifier Board functions and operation In the amplifier portion of the board, Q2 acts as a level shifter and drives the class A transistor Q13. The voltage source for the class A stage is from Q14 and is regulated by Z1. This constant voltage causes Q13 to act as a constant current source and stabilizes the output transistor bias regardless of changes in the AC mains. The class A drive voltage is also removed from Q13 anytime the local or global mute circuits are activated. In the un-muted state CLA-MUTE is 12V. When activated this line goes high to +12V which removes Q14s base voltage when Q25 is turned on. The bias temperature tracking is from diode D8 and the initial setting is made by adjusting RP1 for a voltage reading of .5 to 1.0 mV across either R51-R53 or R44-R45 after the unit has been on and running for a minute or two. A better method of setting the bias is to use a distortion analyzer and adjust the amplifier output for 1 volt at 2 kHz into an 8 Ohm load. After the amplifier has been on and allowed to warm up for a few minutes, adjust RP1 until the crossover notch just starts to disappear. The output section is a complimentary feedback pair topology with Q9 and Q7,Q8 in the positive leg and Q12 and Q10,Q11 in the negative leg. The advantage of this configuration is higher peak output voltage and, because the emitters of the driver transistors become the effective output of the amplifier, crossover discontinuities are very fast and almost negligible without any bias setting. With the bias correctly adjusted the transition through the crossover region is seamless and the very low bias current holds the output stage dissipation to approximately 1 watt. Output stage V-I limiting is through Q5 and Q6. The short circuit current limit is approximately 10 Amps and is set to this high value in order to handle the out of phase currents in highly reactive loads. At high output voltages, however, R37 increases this limit to 20 Amps. For short circuit loads where the current is very high but the output voltage is close to zero, Q4 is turned on and the PROT line activates the local signal mute circuit. This mute removes the output signal momentarily and then releases, cycling on/off until the fault is removed. To verify the short circuit protection, drive the amplifier to an output of 5 volts or more and short the output terminals together. The shorted channel output should cycle on and off and the front panel status indicator should toggle between green and amber. To increase the efficiency and reliability of the amplifier, multiple voltage rails are made available to the output transistors. This addition of variable power supply voltages to the amplifier circuit creates what is known as a class H amplifier. In conventional amplifiers the output devices are simultaneously exposed to high voltage and high current. The product of this current and voltage is dissipated in the form of heat. To make matters worse, the efficiency of the amplifier is the poorest at lower power output levels. To side step this problem the class H amplifier greatly improves the efficiency by running at low power supply voltages when the signal level is low. The operating voltages increase only as required by the program material. Another benefit is in the form of reliability under demanding conditions. Because the output transistors are never exposed to the maximum positive and negative supply voltages at the same time, the amplifier is able to withstand both very high current, under short circuit conditions, as well as highly reactive currents presented by some speakers. With the overall efficiency gain, amplifier heatsink requirements are reduced by half. Arcam P-1000 Amplifier Board functions and operation With the amplifier operating at low output levels (<20 W) only the +/-20V low voltage rails are used. As the output requirements increase, the COMM signal from U2-A also increases and the peak value of this signal is compared to the low rail reference voltage at the comparators U4-A and U5-B. When the peak value of the COMM signal exceeds the reference the comparators will toggle on and the middle rail voltage will be supplied to the amplifier. For a positive signal, Q15 and Q17 turn on the 40 volt supply and on the negative swing Q23 and Q19 supply 40 volts. As the requirements continue to increase the same sequence takes place for the +/- 60 volt supplies. U4-B, Q16 and Q18 supply the positive voltage and U5-A, Q22, Q20 and Q21 supply the negative voltage. The power diodes D7,D23 and D24,D25 isolate the high voltage supplies from the lower voltage supplies. Under short circuit conditions the COMM line signal goes to zero because of the mute drive to Q1 and only the low voltage supply is present at the output transistors. To verify the correct operation of the commutator circuits drive the amplifier to 30-35 Vrms into an 8 Ohm load at 200 Hz and observe the positive and negative supplies. The positive rail voltage is monitored at the emitter of Q18 or at the junction of D7, D23 (cathode ends). To monitor the negative rail use TP2 which is connected to the junction of D24, D25. The waveforms should appear as shown in figure XX. If any of the rail voltages fail to operate, the output of the amplifier will be limited to a lower value by the clipping eliminator circuit. Because of this and the fact that the output will still be a sine wave, it may be necessary to remove the 8 Ohm load to determine which rail is not switching. FIGURE 1 POSITIVE RAIL SWITCHING WAVEFORM FIGURE 2 NEGATIVE GOING WAVEFORM FIGURE 3 BIAS CONTROL AT MAX CCW POSITION FIG 4 BIAS PROPERLY ADJUSTED (COLD) P-1000 Display Board functions and operation. The P-1000 display functions are divided into two separate blocks, power on/off and channel status indications. The power on/off LED indicators are driven by the Standby Power supply on the main board and are active any time the P-1000 is connected to the AC mains supply and the rear panel power switch is on. The Channel Status LEDs receive power from both the Main power supply and from each individual amplifier channel. With the P-1000 connected to the AC mains with the power switch on, the PWR-LED line is high which turns on the red Standby LED on. It also turns Q2 on which forces the run LED off. When the unit is turned on via the front panel power button or the rear panel 12V trigger PWR-LED line goes low and +12V from the main power supply turns on the green run LED. The amplifier channel status LEDs, at turn on, are driven by the FLT lines and show amber for approximately 2 seconds. When the turn on mute cycle has finished the FLT lines go low and the LEDs receive their power from the 12V supply and are illuminated green. If one of the amplifier channels becomes hot enough to thermal out the FLT line for that channel will go high until that amplifier channel cools down. During the off time the status led will show amber. Other channels are not affected by this action. If one of the amplifier channels has a short circuit across the output terminals the FLT line will be activated momentarily and the status LED will alternate between amber and green. This amber/green cycle will continue as long as the fault is present and the amplifier is trying to run program material. When the fault is removed the LED for that channel will return to a steady green. No other channels are affected by this action. In the event of a DC offset fault from the amplifier, the OFFSET line goes high which turns on both LEDs and the color changes to a steady amber. A DC fault condition will also shut down the main power supply. This removes the power to the status LEDs and all the channel indicators will go off. Although it very unlikely that a DC fault will ever take place, it does trigger a latching circuit that receives its power from the standby supply. This means that it will be unaffected by the front power button or the rear panel 12V trigger. The only way to clear this condition is to completely remove the power either by turning the unit off via the rear panel power switch or by disconnecting the AC mains cord for a few minutes. This allows the offset latching circuit to reset to the off state. Arcam P-1000 Main Board functions and operation In addition to the high current supply voltages for the seven amplifier channels, the Main board also contains the circuitry for power on/off control, DC fault protection, the standby housekeeping power and other control circuits as well as the bussing interconnections to all channels. Since the P-1000 is a multi rail class H amplifier, the Main board has three high power plus/minus voltage supplies for the amplifier output stages. The +/- 12V for the signal level amplifier circuits is obtained from the +/- 20 volt low rail supply. These 20 volt low rails are also fused for added DC fault protection but under no operational conditions including amplifier output short circuits should these fuses ever fail. The middle (+/- 40V) and high (+/- 60V) rails are capacitive input filters and require no further explanation. Because the middle and high voltage supplies have no direct discharge path to the output stages when the unit is turned off, Q8 and Q9 form dynamic discharge resistors. This serves two purposes. First it discharges the main bulk capacitors when the unit is off and second, this energy is redirected to the +/- 12-volt supplies which eliminates turn off irregularities. Q8 and Q9 function only for a minute or so when the unit is powered down. The standby power supply is functional at all times when the unit is connected to the AC mains and the rear panel power switch is on. The function of the STBY supply is to provide power for the power on/off logic, display and the DC fault circuit. One additional function is to supply the amplifier circuits with a small (less than 1 volt) DC negative bias which eliminates turn on “pops”. This is accomplished through R62 and D15. Because the power requirements of these circuits is so low the power consumption when the P- 1000 is in the standby mode is less than 2 watts. The DC fault circuit, which includes Q2, 3 and 4, is a bi-directional DC level sensing circuit. The output of each amplifier is monitored through the CH1 through CH7 R-C networks. If a positive going DC voltage is present on any of these inputs, Q2 becomes forward biased, turns on and forces Q3 on. Likewise, for a negative going DC fault Q2 operates in a common base mode with R12 holding the base close to ground potential while the emitter goes negative and the circuit is again activated. Because of the positive feedback through R26, Q3 latches on and, through Q4, pulls the base of the emitter follower Q7 to ground. This action shuts down the Opto coupler U3 and the main power supply Triac goes to the off state and turns the P-1000 off. The OFFSET line drives the global mute circuit and the power LED will show as amber. The unit will remain in this shutdown mode until all power is removed for a minute or so until the standby voltage drops close to zero. If the offset circuit is activated, LED D12 on the m