Midas XL4_Main_Service_Manual(1)电路图.pdf

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1、1 Operators if a failure is traced to one of these blocks it should be replaced. No attempt should be made to repair a switch mode block. Repair is only possible by returning the block to MIDAS ENGLAND. All rails are filtered to remove switching noise and connected to the console via diodes. This al

2、lows two power supplies to be connected in parallel to one console; in the event that one supply fails the other will continue to operate normally. The circuit configuration is similar for all rails except for the polarity of some components. The switch mode block output is first shunted by a differ

3、ential filter capacitor network and then fed to a common mode choke. The choke feeds a further capacitor network which filters common mode noise to the chassis. This is followed by a differential choke, a smoothing capacitor network and the power diode. The 48 volt supply does not use a differential

4、 choke; a resistor is used in place of this part. The power supply monitors the voltage on the mains supply at all times. If the mains is interrupted the power supply gives the console automation system advanced warning that the rails will col- lapse. This ensures that the automation is in reset bef

5、ore the 5 volt rail has become to low to operate the system correctly. The mains is rectified by diodes D11, D12, D13 and D14 which feed opto-isolator IC1. The output is smoothed by C87 and inverted by invertor IC2. Resistor R8 and capacitor C88 provide a delayed turn on and diode D15 ensures fast t

6、urn off. The signal is again inverted by the remaining sections of IC2 which are paralleled to provide high drive capability. The power on line is fed by diodes D16 to D20 and pulled logic low by resistor R9; this allows for power supplies to be connected in parallel. 23 3. Mono Input Pod. The input

7、 pod has separate mic and line inputs, hi and lo pass filters, a direct output and a 20 led meter. The mic input signal passes through T filters L1 and L2, via a switchable 20dB pad and AC coupling capacitors C2 and C3 on to the base of low noise transistors Q4 and Q6. Further filter- ing is provide

8、d by capacitors C5, C6 and C7 and pre-set VR1 sets the pad CMR. 48 volt phantom power can be supplied to the input via current limiting resistors R1, R3 and switch SW1. Transis- tors Q4 and Q6 provide amplification of the signal and their collectors form an output to IC1 which functions as a compari

9、tor. This gives a buffered output to the following circuits and ensures the amplification transistors are operating at constant current by providing feedback via transis- tors Q3 and Q5. Transistors Q3 and Q5 form a voltage to current converter and phase splitter in conjunction with the constant cur

10、rent source formed by Q1 and Q2. By providing this balanced current feedback to the amplifier transistors Q4 and Q6 the common mode load resistance seen at their emitters is infinity and the common mode gain of the overall circuit is zero. The differential load is set by the potentiometer VR3 which

11、adjusts the gain of the circuit by 55dB; effectively shorting out the negative current feedback to greater or lesser extents. High frequency stability and constant bandwidth at all gains is assured by capacitors C8, C9, C10 and C12. The mic amplifier output feeds the frequency adjustable hi and lo p

12、ass filters which are second order active networks formed around IC2. The line input signal passes through T filters L3 and L4 and on to the differential amplifier formed by IC3. Pre-set VR6 provides CMR adjustment and capacitors C23, C24, C25 and C28 provide additional high frequency filtering; C29

13、 and C36 provide AC coupling. The signal passes on to amplifier IC4 which provides 40dB of gain adjustment in conjunction with potentiometer VR7. FETs Q8, Q9 and the second half of amplifier IC4 select the mic or line input to pass on to the phase change over amplifier formed by IC7 and FET Q10. Con

14、trol of the mic/line and phase change is achieved by invertor IC9 via transistor Q11 and CMOS switch IC8. IC9 is configured as a pair of bi-stable flip flops which are triggered by switches SW3, SW4, capacitors C65 and C67 and is connected to the automation system via R86 and R83. CMOS switch IC8 al

15、so selects the signal feed to the 20 led meter in conjunction with amplifier IC6. This automatically selects mic or line amplifier to feed the meter if the meter pre change over line is logic high and monitors the input module signal level via the meter post feed if it is logic is low. The meter cir

16、cuit is formed by the peak responding full wave rectifier and buffer IC10 and meter drive IC11 and IC12. 0dB adjustment is via pre-set VR9 and offset adjustment is via pre-set VR10. The direct output signal from the input module is buffered by amplifier IC6 and fed to the differ- ential output ampli

17、fier formed by IC5. Output symmetry is adjusted by pre-set VR8 and high frequency stability into any load is assured by filter capacitors C46, C47, C48 and C49. Further filtering is achieved by T filters L5 and L6 and AC coupling is via C44 and C45. 24 4. Mono Input Module. The input module houses t

18、he analogue insert, EQ, VCA, mute, pan and bus feed circuits along with logic circuits to control routing and other major functions. Audio signals are received from the input pod via differential amplifier IC9 and fed to the insert and EQ circuits. The order of these elements is determined by switch

19、 SW3. ST1 connects the input module to the test input bus: this is for factory or service use only and the links should be set to the “normal” position at all other times. The insert send circuit is formed by the differential output amplifier IC10. Output symmetry is adjusted by pre-set VR1 and high

20、 frequency stability into any load is assured by filter capacitors C46, C47, C48 and C49. Further filtering is achieved by T filters in the console frame and AC coupling is via C44 and C45. The insert return circuit is fed via T filters in the frame to the differential amplifier IC11. Pre-set VR2 pr

21、ovides CMR adjustment and capacitors C52, C53, C54 and C55 provide additional high frequency filtering; C56 and C57 provide AC coupling. The EQ is a 4 band full parametric type for which all the active circuits are housed on two ce- ramic hybrids HD1 and HD2. High performance is achieved by use of l

22、aser trimmed precision resistors and surface mount components. HD1 has the treble and hi mid equaliser, and HD2 has the lo mid and bass. Insert and EQ in/out switching is performed by FETs Q1, Q2, Q3 and Q4 in conjunction with amplifiers IC12 and IC13. The FETs are controlled from the automation sys

23、tem via shift register IC31 and CMOS switch IC14. After the insert and EQ the audio signal is buffered by amplifier IC15 and split to fed both pre fade mute and VCA circuits. The VCA IC16 is controlled from the fader via the vca line and buffer amplifier IC19. Pre-set VR4 sets the nominal VCA gain t

24、o +10dB and VR3 trims the distortion to a minimum. FETs Q5, Q6, Q7 and Q8 create the mute circuit in conjunction with amplifier IC17. Control of the mute and mute indicator is achieved via invertor IC20 and triple input AND gate IC21. The indicator will illuminate at half brightness if the solo in p

25、lace is active and the solo line is not, if the mute all is active or if the mute line is active. If a link is fitted at ST2 the indicator will illumi- nate at half brightness when the VCA gain falls below -70dB. A comparitor IC19 monitors the vca line for this function which can also be used to dri

26、ve a fader start relay RLA1 as an option. When the mute switch SW6 is pressed it triggers a bi-stable flip flop formed by IC20. When this bi-stable activates the mute or the automation recalls a mute via the mute auto and R146 the indicator will illuminate at full brightness. The direct output can b

27、e sourced post fade, pre fade or pre insert and EQ. Switches SW4 and SW5 make this selection and the output level is then adjusted by potentiometer RV13 before being amplified by IC18. Pre and post VCA signals are fed to the pan circuits formed by potentiometer RV14 (+RV114) and amplifiers IC22 and

28、IC25. Six summing buffers formed by IC23, IC24 and IC26 are used to drive 42 of the modules bus sends. Transistors Q12, Q13, Q14, Q15, Q16, Q17, Q20 and Q21 25 increase current drive capabilities of the buffers when required. Crosstalk and noise are kept to a minimum within the module and the consol

29、e bus system by use of an active ground reference system. A “clean” 0VA or noise reference is sent from the master module to all the input modules. This is buffered by IC27 which provides the active ground reference which is summed into all the bus send circuits and provides a clean earth for all th

30、e aux output potentiometers. VR5 adjusts the DC offset on the active earth to a minimum. This is necessary to reduce transient noise as signals are switched off or on to a bus. FETs Q18, Q19, Q22, Q23, Q25 and Q26 are used to connect pre fade and post fade stereo signals to the solo busses. The FETs

31、 are controlled from the VCA fader block via the solo line and transistor Q24. Switches SW7 to SW21 are used to connect pre fade or post fade signals to the aux send potentiometers RV15 to RV34. These provide adjustment of the current fed on to the bus via fet hybrids HA1, HA2 and HA3. The hybrids p

32、rovide signal on of switching and are located directly above the buss connectors so as to minimise the bus length and crosstalk. They are controlled by automation system via shift registers IC29, IC30 and IC31, and voltage translating hybrids HB3 to HB7. Status LEDs for the aux busses and other auto

33、mated functions are arranged in constant current chains and are controlled from the shift registers via led hybrids HC1 to HC6. The group busses are controlled in a similar way from shift register IC28 via hybrids HB1, HB2, HA4 and HA5. The master buss is controlled from shift register IC31 via Tran

34、sistor Q33 and FETs Q29, Q30, Q31 and Q32. All bus switching is directly controlled from the automation system in the fader tray via data, strobe and clock lines 1 and 2. The status of switch SW27 to SW49 is monitored by the automa- tion system via resistor ladders R250 to R272 and analogue to digit

35、al converter lines 1,2 and 3. Positive and negative references for the resistor ladders are provided directly from the fader tray via +5V switch and 0V switch lines. 5. Stereo Input Pod (option). The stereo input pod has two mic/line level inputs, a gain balance control, hi pass filters, direct outp

36、uts and a two 11 led meters. The mic input signals pass through T filters L1, L2, L3 and L4, to the switchable 25dB pads formed by R9, R10, R11, R42, R43 , R44 and switch SW2. Pre-sets VR1 and VR3 set the pad CMR to a maximum. Switch SW1 connects 48 volt phantom power to the inputs and AC cou- pling

37、 capacitors C3, C4, C21 and C22 connect the input signals on to the bases of low noise transistors Q2, Q3, Q8 and Q9. Further high frequency filtering is provided by capacitors C5, C8, C9, C23, C26 and C27. Transistors Q2, Q3, Q8 and Q9 provide amplification of the signals and their collectors form

38、an output to IC1 which functions as a comparitor. This gives buffered outputs to the following circuits and ensures the amplification transistors are operating at constant current by providing feedback via transistors Q4, Q5, Q10 and Q11. These transistors form a voltage to current con- verters and

39、phase splitters in conjunction with the constant current sources formed by Q6, Q7, Q12 and Q13. By providing this balanced current feedback to the amplifier transistors the com- mon mode load resistance seen by their emitters is infinity and the common mode gains of the overall circuits are zero. Th

40、e differential loads are set by the potentiometer VR1 which adjusts the 26 gain of the circuits by 55dB. It does this by effectively shorting out the negative current feedback to greater or lesser extents. High frequency stability and constant bandwidth at all gains is assured by capacitors C10, C14

41、, C15, C28, C32, C33 and C34. The nominal differential gain of the mic amp is 15dB to 70dB. If the transformer option is fitted the transformer (1:5) provides 14 dB of gain and the active circuit needs to be adjusted to provide the remaining 1dB to 56dB of gain and present a much higher impedance fo

42、r the transformer output. This is achieved by component changes as marked on the schematic. The mic amplifier outputs feed the balance pan circuits formed by amplifier IC2 and potentiometer RV2. This provides up to 10dB of reciprocal boost and cut. The balance pan outputs are then fed to the frequen

43、cy adjustable hi pass filters. These are second order active networks formed around amplifier IC3 and adjusted by potentiometer RV3. The filter outputs feed the phase change circuits which are formed by amplifier IC4. These oper- ate in non inverting mode until switch SW4 or SW5 are activated. When

44、this is done FET Q14 or Q15 are switched on causing the appropriate amplifier to operate in inverting mode. CMOS switch IC6 selects which signals are feed to the 11 led meters in conjunction with transis- tors Q16, Q17 and Q18. If the meter pre change over line is logic high the meters monitor the m

45、ic amp output and if it is logic is low the meters monitors the input module signals via the direct output lines. The meter circuits are formed by amplifier IC8 which is configured as two peak responding half wave rectifiers and meter drive IC9 and IC10. 0dB adjustment is via pre-sets VR6 and VR9. C

46、omparitor IC11 is used in conjunction with transistors Q22 and Q23 to provide a signal present led drive at -25dBu The direct output signals from the input module fed to the differential output amplifiers formed by IC5 and IC7 via links on socket SK7, SK8, SK9 and SK10. These can select the direct o

47、utput source from the input module or direct from the mic amplifier outputs. Output amplifier symmetry is adjusted by pre-sets VR5 and VR8 while high frequency stability into any load is assured by filter capacitors C53, C54, C55, C58, C71, C72, C73 and C76. Further filtering is achieved by T filter

48、s L5, L6, L7, L8 and AC coupling is via C56, C57, C74 and C75. 6. Stereo Input Module (option). The stereo input module houses the analogue insert, EQ, VCA, mute, pan and bus feed circuits along with logic circuits to control routing and other major functions. Audio signals are received from the ste

49、reo input pod and fed to the insert and EQ circuits via sockets ST1 and ST7. These can be used to connects the module to the test input bus: this is for factory or service use only and both sockets should have their links set to the “normal” position at all other times. The insert send circuits are formed by the differential output amplifiers IC2 and IC4. Output symmetry is adjusted by pre-sets VR1 and VR6 whilst high frequency stability into any load is assured by filter capacitors C3, C4, C5, C6, C17, C18, C19 and C20. Further filtering is achieved by T filters in the console frame and A