M703B — Intercom Pre And Output Amplifier

M7O1B INTERCOM PREAMPLIFIER The M7O1B preamp]ifier is des igned to a ccept either dynamic microphone carbon microphone or standard ine Teve 1 input and deliver constant +8 dBm nomina ] output over 30 dB input range variation Input Selection and Control Input selection 0 f either dynamic microphone or carbon (amp]ified dynamic) microphone may be achieved either Toca]ly by switch Tocated on the modu le or eTse remotely from key pane] station This is to ccommodate operator headsets equipped with either type 0 f microphone SW101 and SW102 , both located at the upper edge 0f the module , are used t0 select the input mode 0 f the M7O1B _ ..

. s With SW102 in the LINE position the effects o f SW101 are overriden and the modu ]e is operating in the LINE mode on ;. account 0 f the fo]owing facts: `[ . -The base 0f Q106 is grounded via CR102 , preventing " operation 0 f K101 _ the 0 f ^ ` ~R134 is grounded adding 10 dB Toss at output U101a_ switched and : .

-Q101 and Q102 are OFF , Q103 Q104 are switched On resulting in Toss pad R107 to R1ll being inserted into the input path. . R134 ~:^ With SW102 in MIC position , is removed from ground . potentia] and Sw101 is enab Ted_ pos ition , 6; With SW1o1 enab led and in DYNAMIC J ^ -The base 0 f Q106 is grounded via 0104a .

Teaving K101 : ` de-energized . -Q101 and Q102 are switched 0N , Q103 and Q104 are switched OFF _ resulting in Toss pad R107 to R1ll being bypassed _ .s . ' With SW1o1 enabled and in CARBON position (J103 jumpered to ground or modu ]e connector K connected to ground) :`` ': ;` -Q101 and Q102 are swi tched OFF Q103 and Q104 are switched on inserting loss pad R107 to R111 The base 0 f Q106 is pos itive-biased via U104A causing K101 to energize _ Two separate contact closures o f K101 s 2 -1

M7 01B INTERCOM PREAMPLIFIER Power Supply . . . { .; 0Y ' ` ' ; F^ ` The +25 Vo ]t supply vo]tage enters the unit at pin 1 After pass ing through isolation diode CR105 and resistor R170 , potentia1 0 f 23 vo]ts is developed It feeds the output 1` amp]ifier a $ we71 a $ the Timiter circuits _ Further decoup] ing circuits are employed to generate the necessary voltages to operate 0101 , the Togic circuitry and the carbon mic supply. The M701B draws quiescent current 0 f 40 mA, rising to a pprox imately 75 ma when driving carbon microphones . 2` ' ~ . ^ |

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MFG MFG PART NUMBER U101 U102 U103 U104 Integrated Circuit National LM38IN LM377N LM34BN MM74COO

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MZO1B INTERCOM PREAMPLIFIER Ga in: Dynamic Mic: Carbon Mic: Line: ees 83 dB to 53 dB , t1 dB (Transducer Ga in) _ 33 dB to 3 dB +1 dB (Matched Gain) 28 dB to -2 dB , t1 dB (Bridging Gainj_ s +0 .5 dB from 100 Hz to 5 kHz more than 3 dB down at 10 kHz (tailored response) . Frequency Response: Noise: Dynamic Mic: ...: 120 dBm EIn at maximum sensitivity ' (20 Hz to 20 kHz) _ 50 dB/70 dB be ]ow +8 dBm over 30 dB sensitivity range _ ' . 60 dB / 70 dB below +8 dBm over 30 dB sensitivity range _ Carbon Mic: Line: Ha rmon ic Distortion: Less than 1 % THD from 100 Hz t0 5 kHz at +18 dBm output (Limiter 0FF ) = Input Levels: Dynamic Mic: Carbon Mic: Line: e -75 dBm to -45 dBm . -25 dBm t0 +5 dBm . -20 dBm to +10 dBm . Fn.^ *: ` 3 Input Impedances : Dynamic Mic: Carbon Mic: Line: 1000 ohms nominal, balanced . 150 ohms nomina ] ba Tanced: 10k ohms nomina 7 ba Tanced. . Source Impedances : Dynamic Mic: Carbon Mic: Line: . 150 ohms ba lanced/unba ]anced . 150 ohms maximum , ba lanced/unba lanced 600 ohms maximum , ba lanced/unba lanced. Output Level: +8 dBm nomina ] +22 dBm maximum.

Output Impedance: Less than 50 ohms nomina7 ba Tanced _ 1-1

MZ 02B INTERCOM OUTPUT AMPLIFIER Ga in: To Speaker Output: To Line Output: ^t > '. : +27 dB to +7 dB , t1 dB (Bridging +15 dB t0 -5 dB , f1 dB Gain}: (Bridging '. Sec : " 7. - +1 dB from 100 Hz t0 5 kHz _ 1 Better than 72 dB be ]ow watts or +18 dBm (ga in set at unity for Tine output or 17 dB for speaker output) (20 Hz to 20 kHz ) _ Frequency Response : No ise: Harmonic Distortion: Less than 1 % from 100 Hz to 5 kHz at watts or +18 dBm output.

Input Leve] : +8 dBm nomina7 _ +20 dBm maximum_ Input Impedance: 10k ohms ba lanced and center-tapped _ Source Impedance: 600 ohms or ess ba Tanced/unba Tanced Output Levels : Line: Speaker: +8 dBm nomina 1 +22 dBm maximum. 300 mW nomina 7 3 watts maximum ( +34.77 dBm) Output Impedances Line: Speaker: Less than 25 ohms ba lanced .

Less than 0 .5 ohms unba Ianced _ Load Impedances Line: Speaker: 600 ohms nomina ] 100 ohms minimum. ohms nomina ] Muting: Ful]: Part: Override: s . ' d 100 dB down. 6 to 24 dB down . fu11 output _ - 6 -1

MZO1B INTERCOM PREAMPLIFIER Load Impedance: 600 ohms ba lanced _ ' ' : ` Limiter: e Range S]ope: Threshold: s 30 dB _ NominalIy 3 :1 for the first 10 dB 0 f Timit- ing increas ing to 6 : 1 or better at 30 dB Set a t 5 dB above nomina 7 operating Teve1 , resulting in constant output 0 f +8 dBm under dynamic conditions 10 milliseconds nomina] seconds nomina] 4' ` ` Attack Time: Release Time Phas ing: Input termina] #3 is in phase with output termina 1 #8 Power Requirements : +25 voIts dc, 40 ma nomina ] 75 MA when driving carbon mic. .- Ambient Temperature: 0 to 60 degrees Celsius - , s Dimensions : 0 7" wide X 4 .4" high x 11" deep (18 mm 112 Mm X 280 mm). ^ .sa e ` . : . . ` 6`

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MZO1B INTERCOM PREAMPLIFIER result in +12 Vo ]t open circuit voltage being ': . applied to connector pin 3 and ground potentia] s imultaneously being applied to pin 4 _ With carbon microphone connected to the amp]ifier, approximately voIts at 40 mA is supplied to the carbon element Three to four microphones may be operated in paraiiel without degredation When operating in this mode the amp]ifier presents center-tapped Toad of approximately 150 ohms to the source This Provides 1ow impedance input Tine , assuring minimum coup] ing and crosstalk.

If remote contro] 0 f carbon/dynamic selection is desired J103 is left open a $ norma ] Iy supp]ied and connector pin K is extended to the associated intercom pane1 SW101 must rema i n in CARBON pos ition its action effectively be ing transferred to the remote Tocation When using amp] i fied dynamic microphones jumpers J101 and J102 are cut to rajse the supply voltage and the input impedance to pproximately 1000 ohms To prevent dama ge to the microphone amp]ifier attention should be paid to voltage polarity (pin 3 is positive) _ Preamplifier "3: , ^ ` The secondary 0 f T101 coup]es the audio $ igna ] to preamp]ifier U101A .

The gain 0 f the preamp] i fier may be varied over 30 dB range to accommodate different microphones and operating conditions R132 is the sensitivity contro] and varies the amount 0 f negative feedback around U101A through the resistive network R127 to R132 . : . `es Limiter . ' . The s igna ] output from U1014 is coupled to the isolation amp]ifier 0101B via C112 and Toss network comprising R133 R134 R135 , R136 and Q107 .

Q107 serves a 5 the variab le resistance element a t the output 0 f the Timiter circuitry. The output 0 f 0101B is fed via C118 and LIMITER switch SW103 to the LIMITER thresho ]d contro] R161 The setting 0 f this contro] determines the output Teve1 at which Timiting wi11 begin _ The contro] is adjusted S 0 a $ to result in relatively 2-2

MZ02B INTERCOM OUTPUt AMPLIFIER output appears at pins 21 and Y _ 6 : s :.~ An actively balanced +8 dBm 60 0 ohm output is derived between the and B sections 0 f 0204 and is brought out at pins W and X. This output is capab ]e 0 f driving up to 6 headsets , each having an impedance 0 f 600 ohms 4 ^` R251 contro]s the amount 0 f negat ive feedback app]ied to the A section 0 f 0204 _ It serves as ga in trim contro] a]owing *10 dB adjustment range from the nomina / output Teve]s of +8 dBm or 300 mW respectively _ .

., Power Supply Decoupling ' , ^ | . | 0 `. The modu le is powered by +32 Vo]t dc unregulated power source connected t0 pins 13 and P After pass ing through isolatfon diode CR105 and fuse F201 the supply voltage is decoupled by R236 C212 and C213_ DS201 serves as visua ] POWER ON indicator, verifying that power is supp]ied to the modu ]e and fuse F201 is intact.

[ Q202 Provides further filtering and reduces the supply voltage to 12 volts to operate U201 and U202 _ <'; Under idling conditions , the M702B draws approximately 40 mA = rising to 350 ma at 3 watts output With the output shorted, the current Wi1l initially rise to 750 mA_ settling at 300 to 400 mA as therma 1 shutdown 0 f U204 sets in 4_ A short circuit at the amp]ifier output wi1] nbt norma ]ly blow fuse F201, a$ Tong a$ the amp]ifier i$ operating: with norma 1 program materia] However sustained full output into short circuit or fajlure 0 f U204 will cause the fuse to open .

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M701B INTERCOM PREAMPLIFIER PART DESCR PTION MFG MFG PART NUMBER C1o1 C102 C103 C104 C105 Capacitor 22 uF/25 Kemet T3900226M025AS a.. :. T390B105M035AS T390B225M025AS T390B105MO35AS 4. . e 426ETF22 '` T390B105MO35AS ' 2222-638-10159 : ; 2222-638-70689 T39OB1O5MO3SAS S .. i' T3900336M010AS T390B105M03SAS ' '^ :' . T390B225M025AS t { . 2222-638-70101 . . 2222-638-10109 T390C106MO25AS` J:. ^ ' : T390B105MO3SAS 7.` 426ETF22 7:` T390B225M025AS _ Co9z-MC-153M ` .3 cQ92-MC-427M 0 426ETF22 P3 ` 2222-638-70101 4.

2222-630-0331 7s 4'.: 2222-638-70151 426ETGIOO n^ 426ETF1O0 . :: T39OF107MO16AS uF/35 2.2 uF/25 uF/35 C106 C107 C108 C1o9 C110 22 uF/25 uF/35 15 pF 68 pF uF/35 Philips Kemet Philips Kemet C111 C112 C113 C114 C115 33 uF/10 uF/35 2.2 uF/25 C116 C117 C118 C119 C120 100 pF 10 pF 10 uF/25 Philips Kemet C121 C122 C123 C124 C125 uF/35 22 uF/25 2.2 uF/25 0.015 uF Philips Kemet Aselco C126 C127 C128 C129 C130 4700 PF 22 uF/25 100 PF 330 pF Philips C131 C132 C133 C134 C135 C136 150 pF 100 uF/40 100 uF/25 V 100 uF/16 47 PF Kemet Philips 2222-638-70479 ' 5-1