Sennheiser-MKH20_MKH70-mic-sm 电路图 维修手册.pdf

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1、SA 050418 Subject to alterations Sennheiser electronic GmbH KS 20, 30, 40, 50Capacitance: 40 to 45pF Type 2; KS 60, 70Capacitance: 30 to 35pF Checking the insulation Capsule connections (bottom view): Use a multimeter (20M range) to measure the capsule resistance. R20M (out of range) 1 2 3 1 2 3 MKH

2、 20.70 6/5304/2005 Circuit description MKH20.70 RF bridge circuit (capsule bridge) In connection with the windings 1-2 and 3-4 of the RF coil L1 the push-pull capsule forms a bridge circuit. Each displacement of the diaphragm by a sound signal changes the two capsule capacitances in the respective o

3、pposite direction, resulting in a proportional RF voltage at the bridge output 2/3. L3 compensates the reactive component of the bridge output impedance, so that the bridge output becomes a real and low-resistance output. Using the coil core of L1 the bridge is balanced by changing the winding induc

4、tances in the respective opposite directions, so that the bridge output voltage becomes zero when the diaphragm is in its neutral position. This is the case when the direct voltage between the measuring points A and B becomes zero (balance). The bridge output signal is transformed by the RF coil L2

5、and decoupled from ground. Its primary winding 13-14 is roughly tuned to the oscillator frequency by C1. A fine-tuning with the core of L2 is not required, since the circuit is highly attenuated by the low bridge impedance. For optimum coupling, the core should be positioned in the center of the coi

6、l. Together with the tapping 16/17 of the secondary winding 15-18 the switch makes it possible to achieve a signal attenuation of 10dB (pre-attenuation). The demodulator and oscillator circuits of the microphones MKH20.50 and MKH60.70 only differ with regard to different component references. In the

7、 following sections, data that exclusively apply to the MKH60.70 are put in parentheses. Demodulator Via L2 the RF bridge signal is supplied to the demodulator with D1, D2, and C5, C6 (or C3, C5) and the symmetrical windings 5-6 and 7-8 of L1. The demodulator operates as a synchronous rectifier putt

8、ing through the RF signal of L2 to C6 (or C5) during one half-wave, while blocking it during the other half-wave. The rectified voltage at C5 (or C3) biases both D1 and D2 to such an extent that they will securely block even signals with a higher intensity. The rectified voltage is stabilized with D

9、3, D4 (or R6, R9). When zero balancing is correct, the direct voltage between the measuring points A and B reaches zero, and half the rectified voltage is supplied to C6 (or C5). Depending on the direction of diaphragm displacement the bridge output voltage is either in phase or opposite in phase to

10、 the voltages at the diode windings 5-8. The synchronous rectification results in an increase or decrease of the voltage at C6 (or C5) corresponding to the diaphragm movement. Oscillator The frequency of the RF oscillator results from the capsule capacitances and the inductances of the L1 windings 1

11、-2 and 3-4 and ranges from about 6.5 to 7.5MHz. The collector winding 9-10 and the feedback winding 11-12 couple the oscillator transistor T1 (or Q1) to the capsule circuit. R1 prevents generation of parasitic os- cillations in the VHF range. C2, C3, C4 (or C2, C4, C10) are used for RF blocking, L4

12、(or L5) acts as an RF choke. The operating current of the microphone flows through the oscillator and is stabilized to 2mA by T2 (or Q2), R3, R4, and R5 (constant-current circuit). The NTC resistor R5 stabilizes against temperature influences. R2 ensures a sufficiently high collector voltage of T2 (

13、or Q2), since the base-emitter voltage of T1 (or Q1) is negative (Class C mode). MKH 20.70 04/20057/53 AF amplifier MKH20.50 Since the AF circuits of the microphones MKH20.50 and MKH60.70 differ considerably, they are described separately in the following sections. The amplifier in the MKH20.50 oper

14、ates with the complementary transistors T3 (or Q3) and T4 (or Q4) in push-pull Class A mode. On the DC side, the transistors are connected in series, on the AC side they are connected in parallel via C12 and C14. This increases the available AC output current, enhances the linearity, and reduces the

15、 background noise. The base voltage divider R17, R18, R19, D5 determines the operating voltage of the amplifier and stabilizes it against temperature influences. The AF signal of the demodulator is supplied to the amplifier input via the high pass C19, R16, and C11. The amplifier output is connected

16、 to the microphone output via C15, C16, R22, R23, and the RF barrier L6, L7, and C17 to C20. The output impedance is mainly determined by R22, R23, and the resistive portions of L6 and L7, and is about 150. The Z diodes D6 to D8 protect C14 to C16 from overvoltages. For each microphone type, the fre

17、quency response of the capsule is equalized by frequency-dependent negative-feedback circuits described for the individual types in the following sections. Equalization for MKH20 The series resonance circuit L5, C7, R7 in connection with R9 and R14 causes a treble emphasis with a maximum at 20kHz. I

18、n the S2 standard position, R9 is short-circuited and only R14 is effective. If S2 is opened (diffuse-field correction), R9 is in series with R14 and causes a higher treble emphasis. R13 and C8 correct the frequency response in the center frequency range. Equalization for MKH30.50 The series resonan

19、ce circuit L5, C7, R7 in connection with R9 causes a treble emphasis with a maximum at 20kHz. In addition, C9, R11, and R12 cause a bass emphasis. In the S2 standard position, R11 and R12 are connected in parallel. If S2 is opened (bass roll-off), only R12 is effective and the bass emphasis is reduc

20、ed. R13 and C8 correct the frequency response in the center frequency range. AF amplifier MKH60.70 The amplifier integrated in both the MKH60 and the MKH70 is a two-stage amplifier. The pre-amplifier with T3 (or Q3) equalizes the capsule frequency response. The output stage operates as a high-pass f

21、ilter at low frequencies. The AF output signal of the demodulator is supplied to the base of T3 (or Q3) via the high-pass of C6, C7 in connection with the base voltage divider R10, R11. S2 can be used to switch the operating frequency of the bass roll-off. Frequency response equalization for high fr

22、equencies is realized by the negative-feedback network R9, R12, R13, C8, and L4. S3 can be used to switch the operating frequency of the treble emphasis, so that the result is either a neutral frequency response or a frequency response with treble emphasis. The collector resistance of T3 (or Q3) res

23、ults from the dynamic internal resistance of the oscillator circuit and is very high in the AF range due to the current stabilization. The output signal of the pre-amplifier is supplied to the output stage via C12 and C13. The output stage operates as an active high-pass with voltage amplification 1

24、. The quality is determined by a positive feedback via R14 in interaction with R15 and R17. T4 (or Q4) and T5 (or Q5) operate in complementary push-pull Class A mode. On the DC side, they are connected in series, on the AC side, they are connected in parallel via C14 and C16. This increases the avai

25、lable AC output current, enhances the linearity, and reduces the background noise. The base voltage divider R15, R16, R17, D3 determines the operating voltage and stabilizes it against temperature influences. MKH 20.70 8/5304/2005 The amplifier output signal is supplied to the microphone output via

26、C17, C18, R20, R21, and the RF barrier L6, L7, and C19 to C22. The output impedance is mainly determined by R20, R21, and the resistive portions of L6 and L7, and is about 150 in the center frequency range. The Z diodes D4 to D6 protect C16 to C18 from overvoltages. Output circuit During phantom sup

27、ply, each of the two cable strands supplies half of the operating current to the microphone. The divided operating current is merged by the two resistors R20 and R21 (or R18, R19) with identical resistances. The current flows back to the phantom supply source via the amplifier circuit (MKH60.70: via

28、 both amplifier stages), the oscillator, and the cable shield (microphone ground). Since the operating current is stabilized by the oscillator circuit, the AC side of the amplifier circuit is decoupled from ground (electronic choke) and the available output signal is floating. The signal is balanced

29、 by means of the two supply resistors (6.8k each) of the phantom supply source. MKH 20.70 04/20059/53 Test instructions Measuring and test equipment 1 AF generator, output voltage 1V 1 AF voltmeter, 10mV range 1 oscilloscope 1 handheld multimeter, range 2VDC 1 capacitance meter, 0 to 100pF 1 ohmmete

30、r, range 20M 1 headphones Measuring set-up Test procedure Circuit test MKH20/MKH30/MKH40/MKH50: ?Operating voltage microphone: Check voltages between R22 or R23 and ground; desired value = +41V; both voltages have to be identical. If the no-load voltage of the phantom supply device is not 48V, the d

31、eviation from the desired value has to be identical. ?Current consumption microphone: Check voltages via R20 and R21; desired value in each case = 3.3V (corresponds to a current of 1mA in each case); both voltages have to be identical. ?Balancing: Check the voltage between the measuring points A(+)

32、and B(-); desired value = 0V If the value is not 0V, rotate the coil core of L1 until the voltage is 0V. ?Operating voltages output stage: Check voltage via D6; desired value = 9V Check voltage via D8; desired value = 8V ?Operating voltage oscillator: Check voltage via C4; desired value = +28.5V Dev

33、ice under test phantom supply amplifier 48 V oscilloscope voltmeter headphones MKH 20.70 10/5304/2005 Circuit test MKH60/MKH70: ?Operating voltage microphone: Check voltages between R20 or R21 and ground; desired value = +41V; both voltages have to be identical. If the no-load voltage of the phantom

34、 supply device is not 48V, the deviation from the desired value has to be identical. ?Current consumption microphone: Check voltages via R18 and R19; desired value in each case = 2.2V (corresponds to 1mA in each case); both voltages have to be identical. ?Balancing: Check the voltage between the mea

35、suring points A(+) and B(-); desired value = 0V If the value is not 0V, rotate the coil core of L1 until the voltage is 0V. ?Operating voltage output stage: Check voltage via D4; desired value = 4.5V Check voltage via D5; desired value = 4.5V ?Operating voltage oscillator: Check voltage via C10; des

36、ired value = +30.5V SA 050418 Subject to alterations Sennheiser electronic GmbH & Co. KG 30900 Wedemark Phone: +49 (5130) 600 0 Fax: +49 (5130) 600 30011/53 MKH 20 P 48 service manual MKH 20 P 48 Brief description The MKH 20 P 48 is a high-frequency condenser microphone with omnidirectional characte

37、ristic. Features Very low noise for highly dynamical recordings Distortion-free transmission of sound pressures of up to 142dB Transmission range 20 to 20000Hz Balanced transformer-free signal decoupling Switchable diffuse-field correction for recordings outside of the diffuse-field distance Switcha

38、ble pre-attenuation MKH 20 P 48 12/5304/2005 Controls Technical data NoteThe values in parentheses apply to activated pre-attenuation (-10dB) Acoustic principle_ Pressure receiver Directional characteristic _ omnidirectional Transmission range _ 20 to 20000Hz Free-field no-load transmission factor a

39、t 1kHz _ 25mV/Pa (8mV/Pa) = -32dBV (-42dBV) Equivalent sound pressure level according to DIN 45500, curve A_ 10dB (18dB) according to DIN 45405/CCIR 468_ 20dB (28dB) Max. sound pressure level _ 134dB (142dB) Output _ balanced, transformer-free Electrical impedance at 1kHz _ 150 Min. terminating impe

40、dance _ 1000 Pre-attenuation _ 10dB, switchable Diffuse-field correction_ switchable Infrasonic attenuation _ 18dB/oct below 20Hz Plug-in connection _ XLR3 Connector layout _ 1: -, housing 2: +, AF+ 3: +, AF- Power supply _ Phantom supply 48V Supply voltage_ 48V 4V Supply current _ 2mA Dimensions (i

41、n mm)_ 25 x 150 Weight_ approx. 100g Scope of delivery _ 1 microphone MKH 20 P 48, 1 floorstand clamp MZQ 40, 1 close-talking and wind protection MZW 41 MKH 20 P 48-10 dB diffuse-field correction switch for 10dB sensitivity reduction MKH 20 P 48 04/200513/53 Frequency response Polar diagram diffuse-

42、field correction activated Wirkung der Diffusfeldkorrektur MKH 20 P 48 14/5304/2005 Exploded view 003 010 009 008 013014 012 S001 012 S002 006 007 005 004 004 002 001 015 011 PosDesignation 001Easy release clamp 002Thread insert 003Damping ring 004Countersunk screw hexagon socket M2.5x4 005Housing M

43、KH20 006Metal screw ST2.2x6.5 007Connecting shell for XLR3 008Chassis complete 009Countersunk screw M2x3 010Condenser capsule KS20 011Type plate MKH20 012Brace 013IC mounting DIL6 014Plate 015O ring 18x1 (for condenser capsule version 2) S001Slide switch S002Slide switch MKH 20 P 48 04/200515/53 Sch

44、ematic representations 3-6079-1L23-6079-1L2 MKH 20, component side MKH 20, solder side MKH 20 P 48 16/5304/2005 MKH 20, circuit diagram SA 050418 Subject to alterations Sennheiser electronic GmbH & Co. KG 30900 Wedemark Phone: +49 (5130) 600 0 Fax: +49 (5130) 600 30017/53 MKH 30 P 48 service manual

45、MKH 30 P 48 Brief description The MKH 30 P 48 is a high-frequency condenser microphone with bidirectional characteristic. Features Very low noise for highly dynamical recordings Distortion-free transmission of sound pressures of up to 142dB Transmission range 40 to 20000Hz Balanced transformer-free

46、signal decoupling Switchable roll-off filter Switchable pre-attenuation MKH 30 P 48 18/5304/2005 Controls Technical Data The values in parentheses apply to activated pre-attenuation (-10dB) Acoustic principle_ Pressure gradient receiver Directional characteristic _ bidirectional Transmission range _

47、 40 to 20000Hz Free-field no-load transmission factor at 1kHz _ 25mV/Pa (8mV/Pa) = -32dBV (-42dBV) Equivalent sound pressure level according to DIN 45500, curve A_ 13dB (19dB) Equivalent sound pressure level according to DIN 45405/CCIR 468_ 22dB (28dB) Max. sound pressure level _ 134dB (142dB) Output _ balanced, transformer-free Electrical impedance at 1kHz _ 150 Min. terminating impedance _ 1000 Pre-attenuation _ 10dB, switchable Low-cut filter (cut-off)_ 12dB/oct below 30Hz Roll-off filter _ additional 4dB reduction at 50Hz Plug-in connection _