M8200 — Microphone Preamplifier

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MFG MEG PARTNUMBER HANDLE Module Handle WBS B8205-004 LKI To LK3 2 Pin Jumpcr Aptronics 929955-06 PCB Printed Circuit Board WBS 14-212 UI-U3 U4 14 Pin Dip Socket 8 Pin Dip Socket Amp 640357-3 640463-3 WBS recommends the usc of rcplacement parts made by the specified manufacturers for continucd optimum equipment performance 6-5

M8200 MICROPHONE PREAMPLIFIER The overall amplifier gain is adjusted by gain trim control R3S (sec setup and adjustment section for adjustment de- tails). It is normal practice when the external sensitivity control is wired to the M8200 Microphone Preamplifier that R49 set to the full clockwise position: This will then permit the external sensitivity control to provide the full 30 dB range of sensitivity adjustment Aoy output dc offset voltage may trimmed by R3 and R38 down into the microvolt region_ Once set there is little need t0 make further adjustments, only thc cvent that IC U3 is replac- adjustment becomcs necessary adjust R3A first observing the output voltage connector pins 5 and then adjust R38 by observing the output voltage connector pins or E Range trim control R64 is factory set; and typically should only require adjust- ment if the attenuating element LDRI is replaced_ With no external sensitivity control connccted or placed the full clockwise (CW) position set R49 the full cw position as well: Apply kHz test signal and take reference level on the amplifier output: Turn the amplifiers sensitivity control R49 fully ccw and then adjust range trim control R64 for 31 dB attenuation_ This constitutcs (hc control amplifier sctup_ R^ _ "' )' .

. ` Power_Supply_Decoupling .^ The +/-22 volt dc supply voltage appear- ing amplifier connector pins 1s&s and 13&P are isolated from the amplifier circuitry via fusing resistors R68 and R69 The incoming +/-22 volt supply voltages are filtered by C46 through C5I, after which they connect directly to the amplifier stages. Thc output amplifier is capable maximum output +30 dBu into bridging load of 1500 ohms or greater and +25 dBm into single 600 ohm load: Voltage _ControL Amplifie U4 with associated components form control amplifier which scts the current and thercforc the degree of illumination of the LED in the vari- able light dependent resistor LDRI.

The transfer characteristic this amplifier is sct by the transistor clamps Q5 and Q6. The more currcnt that flows through the LED LDR the lower the resis tance of thc LDRI resistor and theref ore thc greater gain provided the pre- amplifier circuit of the M8200_ Regulators USand U6 decouple the input voltagecs +/-20 volts This provides stable reference voltage source for control amplifier U4.

Two input sensitivity adjustments are available: One is R49, located the module directly, and the other_ the external control which connects module connector pins 10, and The total sensitivity range of 30 dB is determined the sum the [Wo control voltages derived from R49 and thc remote sensitivity control. 3"[ The typical quiescent supply current for the M8200 is 80 mA maximum sensitivity and 60 mA at minimum sensi- tivity_ !

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M8200_MCROPHONE PREAMPLLEIER [nput Preamplifie {7 ] C The microphone input cable connects to pins 9 & K of the module connector with thc cable shield wiring to pin L_ The low noise preamplifier is of dual dif ferential configuration made up of Q1 through Q4 and UI_ This amplificr exhibits very low input noise and the same time provides high rejection common mode input signal voltages_ The gain of this preamplifier is deter- mincd by the ratio of R2O and R2I to the variable solid-state resistor LDRI, The low noise characteristics this optically coupled variable resistor the means which the gain (input sensitivity) the input preamplifier may be altered remotcly without affect- ing its low input noise characteristics External phantom power may be simplex- down the microphone cable_ The external 48V dc voltage wires t0 module connector pin and the supply common connects pin (labelled systems ground).

The phantom power voltage is fed through resistor R2 and R3 to the microphone input: When shipped link LK [ the A-B position_ To feed [he volt phantom powcr voltage place link LKI in the B-C position_ 20 dB loss pad_ made of R4, RS and R6 may bc insertcd into the input signal path for applications where high output level condenser microphones are employed (levels greater than 30 t0 "20 dBu).

To insert the loss pad in the signal path place links LK2 and LK3 in the A-B position: The outputs from the preamplifier stages are fed through R22 and R23 to differ- ential amplifier UZA The gain of this amplifier is trimmed slightly by adjusting R26 for low frequency signals and C26 for high frequencies_ common mode rejection greater than 100 dB provided across the audio band The input signal coupled through blocking capacitors C2 to C9 to com- mon modefilter made and C12 through CIS To differential micro phone input signals this filter is virt- ually non effective; but to common mode noise and rf pick this filter has very high degree of attenuation_ Typis_ cally the common mode loss this input filtcr approaches dB 100 kHz and 80 dB at mHz.

Low Pass Filter UZB along with R27, R28 and C28 [hr- ough to C3I form 12 dB per octave low pass filter with dB roll off point of nominal 40 kHz: This helps suppress out of band super sonic interference which may be picked from TV monitors, SCR type lighting systems; etc Zener diodes CRI to CR4 protect the dual differential low noise preamplifier circuitry from input overloading trans ient voltages_ This typically can occur with the application removal of the phantom power voltage.

Qutput C33 couples thc audio signal the output power stage composed of U3A_ U3B and their associated components Two direct actively balanced outputs are provided at module connector pins 4 & Dand 5 & E The output impedance is set to 60 ohms by R42 through R45_

AND SETUE M820Q_MICRQPHQNE PREAMPLIFIER Reference 1L ^ ' ` ~i{; "twi the technical manual If sclf or externally powered condenser microphones arc being uscd then there requirement for the utilization of the phantom power circuitry of the M8200 microphone preamplifier. There is no need t0 make the 48 volt phantom power connection and link LKI on thc M8200 should placed the A-B position (as shipped) Refer to layout drawing B8z00-06-001 for location_ Refer the D8212 Audio Distribution System and Section this manual for initial mounting frame setup: Special attention and consideration must be given the installation microphone preamplifier in the area of input signal lead wiring and dressing_ Care must als0 taken phantom power (48 volts dc) be connected the preamplifier.

77141' ":E1 Mounting ' 4 {~c The wiring connection of the 48 volt phantom power has been configured that if an M8205 or M8206 distribution amplifier is inadvertently plugged into M8200 wired position, damage will occur to the distribution amplifier_ The M8200 may be mounted in any of the twelve amplifier positions the D8212 Audio System mounting frame; The best performance will bc rcalized the left most module slots the matrix mounting frame are utilized.

Microphone Input "/7j & ~vi | The M8200 preamplifier was designed to provide the highest possible perfor- mance t0 microphone signal distribution This performance will reflected directly t0 how well the wiring install ation made; cable run placement (particularly the microphone input) and cable lengths_ 3 The shielded microphone cable connects thc SA4-[46 terminal assembly reference terminals #I5 #16. The microphone shicld ground connects reference terminal #17 (refcr the drawing on page 7-1).

The audio terminal assembly SA14-[46 is used t0 makc the connections t0 the amplifier. See page 7-1. ';to:_U '~ioo Phantom Power Kt . ] 240) An external 48 volt dc low noise power source may be connected to all M8200 preamplifiers terminal assemblies: The positive connection wires the upper right most lug (terminal reference #2) the SAI4-[46 assembly and the com- mon terminal t0 the lug below it labelled system ground (terminal reference #4).

Refer the drawing page 7-[ this manual for all connections. The microphone input cable should run continuously from the SAI4-146 terminal assembly the microphone XLR equivalent receptacle: Low capacity cable such as Mogami 2574 (6 pf /ft)is recommended for long signal runs aPp- roaching 1000 such Belden type cables #8451 (35 pf /ft) for inter- mediate signal runs: 6: 1 If intermediate distribution frame type connections are madc between the microphone prcamplifier input and the Since the power requirements of phan- tom powered microphones is quite low (typically mA less ) rcco_ mmended that only light gauge wire be uscd for phantom power connections (#22 #26 gauge): This is relieve wiring congestion the rear the D8212 moun ting frame

ANDSETUE D8212 AUDQ DISTRIBUTIQN SYSTEM Unpacking Power Supplies arc setfor nominal 230v AC operation (link J2 in place on the M8245 Power Supply) The primary AC fuscs located the rcar the distribution system mounting frame are 0.75 amp slow blow type #BAG Remove cquipment from packing carton and examine for any damage that may have occurred during shipment: Check that all items ordered are as per packing slip and are accounted for: To configure the audio distribution system for the highest possible primary power source reliability, two separate AC circuits should utilized all the way back to the main distribution brea- ker panel; with the breakers connected different primary AC power phases if at all possible: 143; 37'J"7 Grounding "inT .

1 Determine that all M8205 Distribution Amplifiers and M8245 Power Supplies are scated securely in their frame slots and connectors WARNING Do not apply any AC power the assembly until the completc installation scction has been read thoroughly. Refer drawing D8212-02-002 for additional details. Mounting 0{q. the rear thc MF82 mounting frame separate binding post pro- vided for thc mechanical frame chassis and one for the system electrical ground These two points are isolated from each other within the mounting frame_ These two points should event- ually connect together thc audio system station ground point (see dra wing B8212-02-002).

To simplify system installation and setup it is recommended that all distri- bution amplifiers be removed and stored safe location Mount the distribution [rame aS required the equipment rack_ Do not mount above other hcat generating cquipment without due consideration for proper ventilation and allowances for proper unrestricted air flow. The chassis connection should con- nected all other mounting frames and rack cabinetry either directly from the binding post, via the neutral "U" ground connection (the green wire) integral t0 the primary ac wiring Primatx AC Power The IWo AC power cords are the right rcar section of the MF82 mounting frame_ The use of separate chassis and ground wires returned central station ground point will assure system with the minimal amount of AC and possible RF currents circulating the audio ground system: Kccp audio systems ground connections [ree from any AC; video_ control possible RF ground returns_ For North American operation the M8245 Power Supplies are set up for nominal HSV AC operation (link JI in place on the M8245 Power Supply) The primary AC fuses at the rear of the distribution system mounting framc are 1.50 amp slow blow type #BAG.

For International operation the M8245

M8200 MCRQPHONE PREAMPLLELER PART DESCRIPTIQN MEG MFG PARTNUMBER CI To ^ ` Capacitor 47 uF/50 V Philips 035 90015 S' C1O CH C12 CI3 C14 C1S 0.47/100 uF 0.47/100 uF 1500 pF 1500 pF 5-56 pF SOT Sprague 2CZOXTR4ZAMOSOB Aselco CQ92-MC-100-153M Philips 808-32659 C16 C17 C18 C19 CzO 10 uF/35 10 uF/35 V 3300 pF 3300 pF 330 uF/6 V Kemet T39OC I06MO3SAS Asclco CQ92-MC-100-332M Kemet T39OF337MOO6AS pF 56 pF [00 pF 100 pF 10 pF Philips 2222-630-46569 C22 C23 C24 C25 2222-630-58101 2222-630-10109 2-18 pF 47 pF 2200 pF 4700 pF SOT 809-05003 2222-630-34479 CQ92-MC-222M CQ92-MC-100-472M Asclco C3O 2700 pF 47 pF 150 uF/10 V 47 pF 0.47/100 uF CQ92-MC-100-272M 2222-630-34479 T3OOE1577010AS 2222-630-34479 2CZOXTR474MOSOB Philips Kemet Philips Sprague 0.47/100 uF 47 pF 10 uF/35 10 uF/35 10 uF/35 Philips Kemet 2222-630-34479 T39OC106MO3SAS C40 C4I C42 C43 C44 C45 0.47/100 uF 0.47/100 uF 220 pF 47 4F/50 47 uF/5o Sprague 2CZOXTR474MOSOB Philips 2222-630-03221 0' 4 035 90015 6- [