Arcam-ALPHA-10-Service-Manual 电路图 维修手册.pdf

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1、H ALALPHA 10/10P SERVICE MANUAL 1 ALPHA 10/10P SERVICE MANUAL CIRCUIT DESCRIPTION The mother PCB is common for both the A10 and A10P with the exception of the input mode switch and pre-amp output mute relay which are only fitted to the A10 and the power/standby LED and links to parallel the input co

2、nnections to what would otherwise be the pre-amp output for use with a mono link. The amplifier is based on the D290/Alpha 9 design but with lower gain, a higher current and higher voltage driver stage and a high power output stage. The current servo has been improved over the Alpha 9 to be output d

3、evice independent. A micro supervises the amplifier state, switch state and remote control functions. Provision is made for an additional 3rd channel PCB to be added with power supply and protection circuitry access. Input stage The input connections are taken either from the pre-amp connector, LK12

4、X, or the external power amp input on the A10 depending on the position of SW1. On the A10P, the input is taken from the external power amp input only with provision for a mono shorting link by having two parallel input connectors. On the A10, there is a mute relay on the pre-amp outputs which are a

5、lways connected to the pre-amp connector, LK12X. The signal is passed through a low pass filter with a -3dB point of 550KHz at normal gain and 740KHz at low gain. The gain is selected by SW2. C72 and C74 are d.c. blocking capacitors with a -3dB point of 0.7Hz. A d.c. error correction current is inje

6、cted into the base of Q19 and 26 from the voltage servo Z3 and 4, to null any voltage offset at the amplifier output. The input and voltage amplifier stages both run off regulated 15 Volt suppies. The input stage is an NPN differential input, Q18, 19, 25 and 26, with an adjustable current source, Q2

7、1 and 28 which sets the quiescent current through all the stages but specifically the output stage. C37, R58, C49 and R66 keep the input stage and voltage amplifier stable. Q52, 53, 54 and 55 form a current mirror to ensure that the differential input is balanced during normal operation. Voltage Amp

8、lifier The voltage amplifier consists of another differential pair, Q48, 49, 50 and 51. Q48 and 50 are the positive pulling side of the voltage amplifier output and Q49 and 51 pull negative via a current mirror Q8, 9, 10 and 11. The network C12, 36, R74 and 77 give the current mirror gain to compens

9、ate for the fact that Q49 and Q51 is only driven from the low- impedance side of the input stage current mirror. The network ensures a fast, symmetrical slew rate of the voltage amplifier stage. Network C69, 70, R172, 174 ensure the overall stability of the amplifier by reducing the open loop gain a

10、t high frequencies. Second Voltage Amplifier and Driver Stage Q33, 36, 41 and 44 are the next voltage amplifier stage with feedback applied from the output coupled to their emitters. This stage runs on the full supply rail voltages and splits the level shifts the signal via Q2, 3, 5 and 6 to drive t

11、he gates of the output MOSFETs, Q13, 14, 15 and 16. Q2 and 3 simply buffer the inverted signal at the collector of Q36 to drive the low side MOSFETs, Q13 and 15. Q5 and 6 invert the inverted signal at the collector of Q41 and Q44 to drive the high side MOSFETs, Q14 and 16. To ensure that the high si

12、de drive is able to swing far enough to ensure the high side MOSFETs can be driven to saturation, a bootstrap, C5, D41 R57, C78 and D22 boosts the driver stage power supply during positive excursions of the amplifier output. This is inactive at low output voltage swings as any distortion induced by

13、the network would be more audible at such levels. Output Stage Both the high and low side output devices feature over-current protection, Q17, 23, 24, 30 which clamps the gate of the MOSFET it protects. A high current is permitted through the MOSFET for a few milliseconds after which time the curren

14、t is throttled down to about 10A peak. A second current sensing network, Q32 and Q35 activates the over-current protection cut-out if the low side is current limiting for too long, a few hundred milliseconds. The current sensing resistors do not reduce the transconductance of the MOSFETs because the

15、 driver stage is referenced to the MOSFET source. This means that the current through the driver stage is also sensed but this is insignificant as fas as over-current protection sensing is concerned. Auto-bias H ALALPHA 10/10P SERVICE MANUAL 2 Figure 1Block Diagram of Power Amplifier Sense Resistor

16、Comparitor Output Measured Current (blue) Other MOSFET -ve MOSFET 50%49%52% Bias correctUnder BiassedOver Biassed Figure 2 Auto-bias under dynamic conditions The bias is regulated in two modes, one where these is no signal and one when signal is being split between the high and low side MOSFETs when

17、 driving a alternating signal into a load. Under static conditions, Z8 simply compares the sensed current, which includes the driver stage current, with a d.c. mode reference of 13mV. The sense resistor is 0.11 so this corresponds to a current of about 120mA, some of which is driver current. The cur

18、rent through the MOSFETs is about 80mA at this point. The comparator output is level shifted to drive the integrating current servos Z3 and 4. This adjusts the amplifier current so that, on average, the bias level is held at the reference point. Under dynamic conditions, the low side drive will defi

19、nitely be conducting more current than the reference (80mA) for half the signal cycle and will be switched off for the other half. The result is a rectangle wave output from the comparator, Z4. When the output stage is biassed correctly (class AB operation) the comparator output toggles when the cur

20、rent through the sense resistor for the -ve MOSFET is equal to the d.c. mode static reference level and at the half way point of the signal. The result is a perfect square wave output from the comparator. Under these conditions, the +ve MOSFET is also conducting the same amount of current at this po

21、int. If the bias level is lower than the reference, say, at zero (class B operation) then the -ve MOSFET will spend slightly less than half the time conducting at or above the reference level resulting in a rectangle wave output from the comparator at a duty cycle slightly less than 50%. If the bias

22、 level is higher than the reference then the -ve MOSFET will spend slightly more than half the time conducting at or above the reference level resulting in a rectangle wave output at a duty cycle slightly more than 50%. The change in duty cycle away from 50% causes the integrator, Z3 and Z4 to adjus

23、t the bias level via the bias adjusting transistors, Q22 and 29. The integrator has a reference, the a.c. mode dynamic reference, for a bias point slightly higher than for a 50% duty cycle. This eliminates the possibility of the bias being slowly throttled due to component tolerance mismatch resulti

24、ng in a reference which would pull the servo down. A high dynamic bias reference level simply stabilises the bias slightly higher than the static reference but a low dynamic reference causes the bias to drift down to complete throttle. This system works if the signal is a.c., symmetrical and is not

25、a rectangle wave. Certainly, only a.c. signals are passed H ALALPHA 10/10P SERVICE MANUAL 3 Figure 3 Micro Block Diagram through the amplifier due to C72 and 74 d.c. blocking capacitors and on average the signal will be symmetrical. Any short-term asymmetry will be ironed out by the long time consta

26、nt of the integrator. Main Power Supply The main power supply is regulated in two stages. First it is pre-regulated by Q1 and 4 to about 11V less than the main supply rails. This supply is made available to an option board. The maximum load on these supplies is 150mA for less than 2W dissipation in

27、Q1 and 4. These supplies are then regulated to +/-15V by Z1 and 2. These supplies are used by the input stages of the power amplifiers including any 3rd channel board, the pre-amplifier board and an optional phono amplifier board. The positive voltage regulator, Z1, has a larger heatsink than Z2 bec

28、ause the phono board consumes much more current from the positive rail than from the negative rail. Control Micro The control micro performs the following functions. Switches the amplifier on or off, Mutes the speakers #1 or #2 or the pre-amp output, Monitors the heatsink temperature, Monitors RF co

29、ntent of speaker outputs, Handles the remote bus and infra red remote input, Reports fault conditions to the main display and LED, Reads the speaker and power switch positions. The control micro runs of the constant power supply from standby transformer, TX2. This enables the amplifier to be switche

30、d on or off remotely from the remote bus or, in the case of the integrated amplifier, from an infra red remote control. This power supply is intended to supply all the digital circuitry in the amplifier including any option boards. This is supplied at 8V to the other boards where it will be locally

31、regulated to 5V as required. The micro communicates with the display board via a multi-master I2C bus. This bus is used to report amplifier and power status to the display micro and remote control commands received. It is also possible for the display micro to control functions on the power amplifie

32、r board. The option board also uses this bus to receive any remote control commands and communicate with the display micro. The external remote bus handles raw information from infra red sensors with no demodulating. The remote bus input can be echoed to the output through a buffer circuit. The inco

33、ming signal is demodulated by Z13. Raw signal is also sent to the micro interrupt line, pin 12, for assessing the noise on the remote bus. In addition, any d.c. signal on the remote bus is sensed on pin 2 of the micro in when it is not being used as an output to mute the hardware remote echo buffer.

34、 The micro must modulate any output it sends to this bus with a carrier (37KHz). The output will drive one or two series infra red LEDs directly. The list below shows how various fault conditions can be deduced simply from the Power LED behaviour. H ALALPHA 10/10P SERVICE MANUAL 4 On power up, the p

35、rotection should be engaged. This is checked after 3 seconds on pin 9 of Z9. If it isnt happening, the unit shuts down with flashing red. If the protection does not clear after about 16 seconds on power-up the unit shuts down to flashing red. This is usually caused by a voltage offset. Any main amp

36、power loss detected on pin 26 after power-up causes a shut down to flashing red. Any RF detected on pin 3 results on immediate shut down to flashing red. Any protection fault detected after power up on pin 9 results in a flashing amber LED for about 16 seconds max. If it has not cleared by then the

37、unit is shut down to flashing red. Protection faults are caused by voltage offset or over-current. Over-current should latch resulting in a shut down after 16 seconds. Voltage offsets should clear themselves if brief. A temperature fault on pin 25 results in the power LED flashing slow amber and can

38、 last indefinitely until it clears. When it clears the flashing will speed up until the protection times back in. ALPHA 10P POWER AMP MAIN BOARD PARTS LIST Ref No.DescriptionPart No C1ELST 100U 100V2N710B C2ELST 100U 100V2N710B C3MLC 100N 50V X7R 10% SM2C410 C4ELST 100U 100V2N710B C5ELST 100U 100V2N

39、710B C6ELST 22U 63V2N622 C7ELST 10U 50V2N610 C8ELST 22U 63V2N622 C9ELST 10U 50V2N610 C10ELST 10U 50V2N610 C11ELST 1U0 50V2N510 C12PPRO 4N7 63V 5% RA2D247N C13SUPPR CAP 4N7 250V2K247 C14PPRO 150P 5% 63V RA2D115 C15ELST 10U 50V2N610 C16ELST 10U 50V2N610 C17ELST 10U 50V2N610 C18ELST TNC 10m 63V RA 40mm

40、2N910A C19ELST TNC 10m 63V RA 40mm2N910A C20PPRO 4N7 63V 5% RA2D247N C21PPRO 4N7 63V 5% RA2D247N C22ELST 100U 25V2N710 C23ELST 100U 25V2N710 C24ELST 100U 25V2N710 C25ELST 100U 25V2N710 C26ELST 100U 25V2N710 C27ELST 100U 25V2N710 C28MLC 470P 100V NPO 5% SM2C147 C29MLC 470P 100V NPO 5% SM2C147 C30MLC

41、470P 100V NPO 5% SM2C147 C31MLC 100N 50V X7R 10% SM2C410 C32ELST 22U 63V2N622 C33ELST 22U 63V2N622 C34MLC 100N 50V X7R 10% SM2C410 C35PPRO 150P 5% 63V RA2D115 C36PPRO 4N7 63V 5% RA2D247N C37PPRO 1N0 5% 63V RA2D210 C38PPRO 680P 63V 5% RA2D168 C39PPRO 680P 63V 5% RA2D168 C40MLC 10N 50V X7R 10% SM2C310

42、 C41MLC 10N 50V X7R 10% SM2C310 C42MLC 10N 50V X7R 10% SM2C310 C43MLC 10N 50V X7R 10% SM2C310 C44SUPPR CAP 4N7 250V2K247 C45ELST 10U 50V2N610 C46SUPPR CAP 4N7 250V2K247 C47SUPPR CAP 4N7 250V2K247 C48ELST 3M3 25V2N833 C49PPRO 1N0 5% 63V RA2D210 C50ELST 1U0 50V2N510 C51ELST 220U 16V2N722 C52ELST 220U

43、16V2N722 C53ELST 220U 16V2N722 C54ELST 220U 16V2N722 C55PCRB 100N 100V 10% RA 5mm2H410 C56PCRB 100N 100V 10% RA 5mm2H410 C57PCRB 100N 100V 10% RA 5mm2H410 C58PCRB 100N 100V 10% RA 5mm2H410 C59PCRB 100N 100V 10% RA 5mm2H410 C60PCRB 100N 100V 10% RA 5mm2H410 C61PPRO 100P 63V 5% RA2D110N H ALALPHA 10/1

44、0P SERVICE MANUAL 5 C62PPRO 100P 63V 5% RA2D110N C63PPRO 150P 5% 63V RA2D115 C64PPRO 330P 5% 63V RA2D133 C65PPRO 150P 5% 63V RA2D115 C66PPRO 330P 5% 63V RA2D133 C67PEST 15N 63V 5%2K315 C68PEST 15N 63V 5%2K315 C69PSTY 56P 160V ENCAP 1PF%2F056 C70PSTY 56P 160V ENCAP 1PF%2F056 C71ELST NON POLAR 10UF 35

45、V2U610 C72ELST NON POLAR 10UF 35V2U610 C73ELST NON POLAR 10UF 35V2U610 C74ELST NON POLAR 10UF 35V2U610 C75PEST 47N 63V 10%2K347 C76PEST 47N 63V 10%2K347 C77PEST 47N 63V 10%2K347 C78PEST 47N 63V 10%2K347 C79ELST NON POLAR 10UF 35V2U610 C80ELST NON POLAR 10UF 35V2U610 C81MLC 22P 100V NPO 5% SM2C022 C8

46、2MLC 22P 100V NPO 5% SM2C022 C83ELST 100U 25V2N710 C84MLC 100N 50V X7R 10% SM2C410 C85MLC 100N 50V X7R 10% SM2C410 C86MLC 100N 50V X7R 10% SM2C410 C87MLC 100N 50V X7R 10% SM2C410 C88MLC 100N 50V X7R 10% SM2C410 C89MLC 100N 50V X7R 10% SM2C410 C90ELST 10U 50V2N610 C91PPRO 680P 63V 5% RA2D168 C92MLC 1

47、0N 50V X7R 10% SM2C310 C93MLC 1N0 50V X7R 10% SM2C210 C94MLC 10N 50V X7R 10% SM2C310 C95ELST 10U 50V2N610 C96ELST 10U 50V2N610 C97MLC 100N 50V X7R 10% SM2C410 C98MLC 10N 50V X7R 10% SM2C310 C99CERD 10PF 63V 10%2A010 C100CERD 10PF 63V 10%2A010 D1ZENER 15V 400MW3C11504 D2ZENER 15V 400MW3C11504 D3ZENER

48、 10V 400MW3C11004 D4ZENER 10V 400MW3C11004 D5ZENER 10V 400MW3C11004 D6ZENER 10V 400MW3C11004 D7ZENER 10V 400MW3C11004 D8ZENER 10V 400MW3C11004 D9ZENER 10V 400MW3C11004 D10RECT FIER 6A40 6A 400V3B6A40 D11RECT FIER 6A40 6A 400V3B6A40 D12RECT FIER 6A40 6A 400V3B6A40 D13RECT FIER 6A40 6A 400V3B6A40 D14R

49、ECT FIER 1N4003F 1A 200V3B4003 D15RECT FIER 1N4003F 1A 200V3B4003 D16SSDIODE 1N4148 75V3A4148 D17SSDIODE 1N4148 75V3A4148 D18RECT FIER 1N4003F 1A 200V3B4003 D19RECT FIER 1N4003F 1A 200V3B4003 D20SSDIODE 1N4148 75V3A4148 D21RECT FIER 1N4003F 1A 200V3B4003 D22RECT FIER 1N4003F 1A 200V3B4003 D23RECT FIER 1N4003F 1A 200V3B4003 D24RECT FIER 1N4003F 1A 200V3B4003 D25RECT FIER 1N4003F 1A 200V3B4003 D26SSDIODE 1N4148 75V3A4148 D27RECT FIER 1N4003F 1A 200V3B4003 D28SSDIODE 1N4148 75V3A4148 D29ZENER 4V7 400MW3C04704 D30SSDIODE 1N4148 75V3A4148 D31SSDIODE 1N4148 75V3A4148 D32SSDIODE 1N4148