USER`S MANUAL - JW Davis & Company
Contents
1. TO REDUCE THE RISK OF FIRE OR ELECTRICAL SHOCK DO NOT EXPOSE THIS UNIT TO RAIN OR MOISTURE UNPACKING AND INSPECTION PROCEDURES This unit was carefully checked and packed before leaving the factory However the shipping container and unit should be inspected for indications of improper handling If the unit has been damaged in transit make an immediate claim to the carrier for their inspection Returning the freight to J W Davis amp Company will void your claim with the carrier I PRODUCT FEATURES The features and benefits listed below make this series of amplifiers unique They have been designed with the user s needs in mind to be products that fit many applications without modifications or additional equipment e f Major Application Interfaces e 6 Switchable Microphone Line AUX or CD DVD Modules e 15 Special Signal Inputs e f Signal Outputs e Power rated by specific model selected e 4 16 Q 25 and 70 Volt System Outputs e 24 VDC Alternate Power Source e Multiple Music On Hold Options e A switch to activate the 400Hz roll off circuit to protect horn drivers e Tape out for recording e Pre out Main In for insertion of signal conditioning equipment such as equalization e Booster out provides a signal for power amplifiers to expand the system e FIVE YEAR WARRANTY NEW TECHNOLOGY gt OLD RELIABILITY y i 7D Davis amp Company e 3030 Canton Street PO Box 710219 Dallas Texas 75371 0219 Sale2. overload protection circuits provide warnings of potential load and input output issues If the amplifier senses unstable conditions resulting from overload or sig nal clipping on the input or output the peak LED will remain on with no output from the amplifier Rack RAK M or wall WM M mounting kits are available as optional accessories 3 NEW TECHNOLOGY gt OLD RELIABILITY y i 7D Dauis amp Company e 3030 Canton Street PO Box 710219 Dallas Texas 75371 0219 Sales 800 527 5705 Fax 800 388 9106 Corp 214 651 7341 e Fax 214 939 0328 sales 9 jwd com www jwd com DES rc te us IV FRONT PANEL DETAIL 0 So o lo 0 So 0 So INPUT3 INF UT4 INPUTS INFUT6 ER JAS a S M 1 2 3 4 9 6 1 8 9 10 11 Input 1 Signal LED Input 2 Signal LED Input 3 Signal LED Input 4 Signal LED Input 5 Signal LED Input 6 Signal LED system Over Ride Signal LED Tel Page Input Signal LED Amplifier Output Signal LED Amplifier Peak Protect LED Amplifier Power LED 4 NEW TECHNOLOGY 12 13 14 15 16 17 18 19 20 21 Input 1 Level Control Input 2 Level Control Input 3 Level Control Input 4 Level Control Input 5 Level Control Input 6 Level Control Bass Control Treble Control Master Volume Control Power Switch Push Button OLD RELIABILITY y DY Dauis amp Company e 3030 Canton Street PO Box 710219 Dallas Texas 75371 0219 Sales 800 527 5705 Fax 8
3. rr ly ON and middle pin PIED d NOTE THE FOLLOWING INPUTS ARE UNIQUE IN THEIR FUNCTIONALITY The Telephone System Over Ride and Music On Hold inputs have their own volume controls and bypass the amplifier s Master Volume Bass and Treble controls which permits the volume levels to be tailored to the specific use Typically telephone paging needs to be set for best intelligibility while adjusting the front Master volume control for background music SystemOverRide is designed for sound masking systems Call J W Davis tech support for this applica tion Another option for the SOR is for signal notification Activating the board level jumper will allow the SOR to mute inputs two through six for use as a signaling device such as a tone generator or alarm signal The Music On Hold input output does not require tone adjustment due to the limited frequency response of telephone handsets 7 NEW TECHNOLOGY ju OLD RELIABILITY y DY Dauis amp Company e 3030 Canton Street PO Box 710219 Dallas Texas 75371 0219 Sales 800 527 5705 Fax 800 388 9106 Corp 214 651 7341 e Fax 214 939 0328 sales jwd com www jwd com y N The Mark of the Professional Usas VII TECHNICAL SPECIFICATIONS Model Number DA 30M DA 60M DA 120M Power Rating Frequency Response 50Hz 15kHz 3dB TEL 250Hz 15kHz 3dB S N Ratio Tone Controls at Center Detent THD MIC XLR F 1 6 150 Q 1 mV or Line XLR F 1 6 B
4. the same at each speaker Fora 120 Watt amplifier the range 40 80 is equivalent to 48 96 Watts Therefore 18 speakers x 4 Watt taps each 72 W Good match 12 speakers x 1 Watt taps each 12W Poor match 60 speakers x 1 Watt taps each 60W Good match 60 speakers x 4 Watt taps each 240W Very poor match overload 90 speakers x 1 Watt taps each 90W Good match POWER LOSS IN LONG LINES For long lines the power loss in watts becomes a significant factor The power supplied by the amplifier is effectively reduced by the line loss For a 0 5 dB loss in sound pressure the total wire resistance must be limited to 696 of speaker impedance The table below shows the calculated two wire cable lengths permissible for a number of wire sizes in feet For a 1 dB loss the lengths may be doubled For 2 dB loss multiply by 4 4 Low Impedance High Impedance Systems Resistance 100W 70 7 V 50W 70 7 V 25W TO 7 V ohms 1000 4 ohms 8 ohms 16 ohms 12 5W 25 V 6 25W 25 V 3 5W 25 V feet 50 ohms 100 ohms 200 ohms om m e 39m o pa e o w 10 NEW TECHNOLOGY ju OLD RELIABILITY fj DY Dauis amp Company e 3030 Canton Street PO Box 710219 Dallas Texas 75371 0219 Sales 800 527 5705 Fax 800 388 9106 Corp 214 651 7341 Fax 214 939 0328 sales jwd com www jwd com JWD Master Ser
5. 00 388 9106 Corp 214 651 7341 e Fax 214 939 0328 sales 9 jwd com www jwd com DES src of he Pi 10 11 12 13 14 15 D lt c BS QU m Cree 2 E years of sound gt XD 2 3 4 5 6 7 8 9 40 11 2 V BACK PA IEA 123456 44 43 46 7 48 9 QO A C Fuse Replace with identical type Music On Hold Output transformer balanced 600 Q 1 V adjustable Telephone Page Input transformer balanced 600 2 100 mV See page 7 Tel Page Volume Control Controls the level of Tel Page input independent from front volume bass and treble controls See page 7 Remote Mute normally open Used with Module 1 MIC allows for a switch to mute Modules 2 thru 6 VOX Controls Variable resistor that controls the VOX Mute sensitivity one for TEL input and one for Module 1 MIC Music On Hold volume control Controls level to on hold circuit of a phone system MOH Switch Allows for the MOH input signal to be shared with AUX input 6 See page 7 HPF Switch Activates the 400Hz Low Cut Filter high pass filter to protect horns Effects main speaker output only SystemOverRide Volume Control Controls the level of SOR input independent from front volume bass and treble controls See page 7 SystemOverRide Input Used for noise masking applications bypasses front volume and tone controls Board level jumper can activate it for priority input muting Modules 2 thru 6 See page 7
6. DOMO MM D CD DVD es NP S 7 AUX ME PERCHE CD DVD SEL z INPUT1 i REC OUT gt REC OUT KR LINE MC TRM26 eun PHAMTOM 150Hz HPF pe e E NUN VII E MS UTI M Vu Pe eye v eec MEME i l aroi L HPN T gt a peu VR BOOSTER Popel mia e gt RUM gt peu ENE 1 55s BASS VR E INPU2 VR m n EL i i i uy I l ak BALANCE nS INPUS VR E es c pr 2 BE 1 poses E MES z INPU4 VR i P PRE OUT a i E lt h ul I iv E RUR NR TREBBLE VR SoTa NNN n AUX lt vee UM LL LLLI QM I rn RRnC MEDI CMM Pun MET POWER IN CD DVD E uteri i o K Y AUX 5 AS CD DVD SEL T INPUT2 r a mE eee KK POWER POWER AMP x 2 peak ed a iy INPUTS SIGNAL d DER iN m ee x i i HEATSINK 1 TERMPERATURE 1 1 SOR PROTECT i rd TEL A EM _ i oT NF M i aaa dns 1 INPUT4 i i 1 1 OVER ROAD SHORT PROTECT KR D6 1 puto mK 07 NPUTS d OUTPUT mR 09 PUTA 4 70v C9 i i R D10 I INPUTS NPUTS 4 l wR Dn NPUT2 4 25V amp x D8 INPUT RED eed Me ot a 4 16R G2 INPUT6 NOTE INPUT3 6 ARE AS THE SAME AS INPUT2 COM amp 1 ER
7. Music On Hold Input Input for MOH source Can be shared with Aux input 6 See pages 3 and 7 51 2 ft Power Cord 120 VAC 15 Amp Chassis Equipment Ground Used in electronic equipment rack Do not ground to A C line 24 VDC In The 24 VDC allows the amplifier to be used with emergency backup power sup plies For portable use or where 120 v not available NEW TECHNOLOGY ju OLD RELIABILITY y P W Dauis amp Company e 3030 Canton Street PO Box 710219 Dallas Texas 75371 0219 Sales 800 527 5705 Fax 800 388 9106 Corp 214 651 7341 Fax 214 939 0328 sales 9 jwd com www jwd com of the Professional sese d NEL DETAIL 21 22 23 24 25 Tidone e CT TD TAS Ua T 15 4 Wu wh caf e LS R 4 Es Ma om y CAUTION SELECT O HE SOURCK PER INPUT Y J ION SELECT ONE SOURCE PER INPUT 2 Y G2 G4 Q5 16 Speaker Output Terminals The available screw terminal outputs are 4 16 Q 25 V and 70 7 V 17 REC OUT Connects signal to a recording device Unbalanced 600 Q 1 V 18 BOOSTER OUT Connects signal to additional power amplifier Unbalanced 600 Q 1 V 19 amp 20 PRE OUT PWR IN The two RCA jacks offer an opening between the pre amp and the power section of the amplifier This allows the insertion of an equalizer or other signal condi tioning equipment Unbalanced 600 Q 1 V MODULE SECTIONS 2 6 21 Auxiliary Input Two channel input will electronically sum stereo sig
8. U AE PIRE A ets a A a RE QE aE RED eaa e e A I a ee A el ey i I ji I BN A O A A A rm TM E A A A A D SA ty A E E E ES A A A E ei al li ic MOH INPUT S u AUN gt MOH VR E SON jj i E I 5 L MOH OUT V THERMAL FUSE V O O OEE ET qoo INSIDE ruse nnnc ne Muir dM Md EE dc MEE DC24V i WGA a A Y A I Db D eer Pee aa KE FUSE2 O AC 120V TEL PAGE INPUT PA TEL MUTE PT H o i clo EE bond FUSE M n DC 24V G AAA SA E AI SS 22 HS ee ei endet A A A SS AY l I I I L amp I SOR MUTE SOR INPUT JUMP I l 1 I I I LED A cuum ID nuca neum ctc ume Ner mr mu EE AO eum meon TA Im eoe mpm Av T m amnem o a A Rl ee re eol mm mm eer mt Ee Se ES A A A E ciere NOTE A detailed schematic may be obtained by contacting our Customer Service Department 9 NEW TECHNOLOGY gt OLD RELIABILITY fj DY Davis amp Company e 3030 Canton Street PO Box 710219 Dallas Texas 75371 0219 Sales 800 527 5705 Fax 800 388 9106 Corp 214 651 7341 Fax 214 939 0328 sales jwd com www jwd com y C495 The Marks of the Professional ad IX TECH NOTES HIGH IMPEDANCE OF 25 AND 70 7 V SYSTEMS The high impedance or constant voltage method of impedance matching uses a high impedance amplifier output which is transformed down to 8 Ohms by an impedance matching transformer at each individual speaker The big advantages of this approach as compared to low imped
9. alanced 10k Q 100 mV MIC TRIM Adjustable MIC Phoenix 1 6 150 Q 1 mV or Line Phoenix 1 6 Balanced 10k O 100 mV MIC TRIM Adjustable Inputs Telephone Page Shielded Transformer 600 100 mV Aux 1 6 2 Channel Audio Electronically Summed to Mono Unbalanced Output 47k Q 100 mV or DVD CD 1 6 2 Channel Audio Electronically Summed to Mono Output 47k Q 360 mV Switchable on Modules 1 thru 6 24 VDC MOH Transformer Isolated 600 QO 0 1 V Adjustable Outputs MIC 1 VOX 37dB Via Switch 7 Mute Send VOX Voice Mute Circuits VOX Sensitivity Adjustable SOR VOX 40dB Via Circuit Board Jumper 700 Remote Mute Terminal Use w MIC 1 37dB Tone Controls Bass 10dB at 100Hz Treble 10dB at 10kHz High Pass Filter HPF Switchable 400Hz 6dB Octave 4 16 Q 25 V amp 70 7 V Outputs Only Indicators Inputs 1 thru 6 Tel SOR Signal Output Peak Signal Output Steady On Amp Protect 4 Power LEDs 120 VAC Power Source 24 VDC Power Consumption 100W 200W 300W Protecti Built In Signal Clip Comparator on Input to Output to Speaker Load en Thermal Overload and Short Circuit Protection H 16 5 W x 13 5 D x 4 3 H 2 RU w o feet Available Accessories RAK M 19 Rack Mount Kit WM M Surface Wall Mount Kit opecifications subject to change without notice 8 NEW TECHNOLOGY 4 gt OLD RELIABILITY fj DY Dauis amp Company e 3030 Canton Street PO Box 710219 Da
10. ance are 1 Reduced line losses and ability to use smaller wire gauges This is due to the higher voltage and reduced current in the speaker lines 2 Much simpler impedance matching procedures and connections Constant voltage is a misnomer in that the amplifier does not always produce 70 V Rather the amplifier output imped ance is set at such a level that irrespective of its rated power it will produce 70 7 Volts output at full power Thus a 10 Watt amplifier optimum load would have an impedance of 500 Ohms P 70 72 500 a 40 Watt amp would be 126 Ohms and 120 Watt amp 42 Ohms Multiple transformer taps allow the impedance at each speaker to be adjusted individually to give a total matched load Because of the high impedance arrangement the system is easier to impedance match and is also inherently less sus ceptible to problems caused by mismatching The transformer taps are marked in W watts instead of Ohms usually 4 2 1 1 2 Again it should be born in mind that these levels of power output are only achieved when the transformer is working at 70 7 Volts The transformers are connected in parallel A good match is obtained by ensuring that the total of all tap settings fits into the range of 40 80 of rated amplifier output 80 is chosen to allow for transformer insertion loss Also It is good practice not to drive the amplifier to 100 of its capacity Examples are shown below For simplicity it is assumed that all tap settings are
11. ction If the amplifier is installed in a permanent location the phoenix type screw terminals should be used for a better long term connection 2 NEW TECHNOLOGY 4 OLD RELIABILITY fj UW Davis amp Company e 3030 Canton Street e P O Box 710219 Dallas Texas 75371 0219 Sales 800 527 5705 Fax 800 388 9106 Corp 214 651 7341 Fax 214 939 0328 sales jwd com www jwd com y VEZ Me Mark of the Professional s ed Three other dedicated inputs described below have independent volume controls located on the amplifier s back panel Neither the Master Volume Control nor the Bass and Treble Controls will affect these inputs 1 Telephone Page input This shielded balanced input accepts the signal directly from the page port out on the telephone system 2 Music On Hold MOH input This input oper ates through a separate dedicated internal one watt amplifier that permits close control of volume levels The music on hold RCA type input accepts the signal from music tape messages company advertisements or other audio sources The MOH signal also can be routed to the main amplifier for distribution to the entire sound system 3 SystemOverRide SOR input This independent input is not affected by any other ampli fier control Its purpose is Priority signaling sound masking and other applications that must not be interrupted by the regular functions of the amplifier The default SOR setting is for sound ma
12. f AEN Id eo he Pepe Y 42 y N of sound service Y Y y mal USER S MANUAL 0 10 h o o o h lo o o o o INPUT1 INPUT2 INPUT3 INPUT4 INPUTS INPUT6 Master Series Amplifiers DA 120M 120 watts DA 60M 60 watts DA 30M 30 watts Unpacking Inspection Procedures 1 VI Settings for Additional Features T I Product Features 1 VII Technical Specifications 8 IIl Operating Summary 2 3 VIII Master Series Block Diagram 9 IV Front Panel Detail 4 IX Tech Notes essere 10 V Back Panel Detail 5 6 X Purchase Information Back Cover NEW TECHNOLOGY gt OLD RELIABILITY j DY Dauis amp Company e 3030 Canton Street PO Box 710219 Dallas Texas 75371 0219 Sales 800 527 5705 Fax 800 388 9106 Corp 214 651 7341 Fax 214 939 0328 sales jwd com www jwd com 090705122 N y Y Y Y The Mark of the Professional SS WARNING DO NOT CUT OR REMOVE THE GROUND PIN ON THE AC POWER CABLE DO NOT USE AC TWO PIN ADAPTER UNLESS IT IS GROUNDED BY AN EXTERNAL GROUND WIRE CHECK THE AC WALL RECEPTACLE TO CONFIRM THE PROPER GROUND IS PRESENT WARNING TO REDUCE THE RISK OF ELECTRICAL SHOCK DO NOT REMOVE THE COVER NO USER SERVICEABLE PARTS INSIDE REFER SERVICING TO QUALIFIED SERVICE PERSONNEL WARNING
13. hable modules example below that provide the desired signal inputs by simply setting the indicated dip switches up or down HDD Terminal Phantom XLR LINE ad AUX Level XLR High Pass Terminal Hi Z Connection Level em Filter Balanced J LOW Z Switch 1 selects the balance of the incoming signal Switch 2 selects either an unbalanced CD DVD or AUX input The two RCA jacks electronically com bine stereo to a mono signal out Either RCA jack may be used to input a single mono signal Switch 3 connects either the phoenix type terminal or XLR connector to the input source RCA Jacks Module 1 Switch 4 selects either a balanced Lo Z MIC or Line level signal input Switch 5 activates the Phantom Power 24VDC to use with condenser or electret microphones Phantom power is available on either XLR or Terminal inputs Switch 6 activates a High Pass Filter on the XLR or Terminal inputs This filter will roll off frequencies lower than 150Hz to reduce the popping sound of a MIC switch or of consonants in human speech Switch 7 available only on Module 1 activates a Mute Send function When activated the MIC source connected to either the XLR or Terminal input will VOX mute the other five modules NOTE Ifthe Amplifier is frequently moved to different locations or used as a portable system the XLR connectors should be used The action of plugging and unplugging the connector maintains a good conne
14. ies Amplifiers Thank you for selecting a J W Davis Master Series Amplifier Since 1933 it has been our goal to produce a complete line of quality products and to offer a FIVE YEAR WARRANTY on most J W Davis items You will not see our products advertised in a discount catalog or other consumer venues since we limit our sales to qualified professionals Having bought through a professional you may use J W Davis amp Company products with confidence and pride For your next installation please consider the other fine J W Davis products such as power amplifiers pre Amplifiers mixers microphones speakers speaker systems horns lecterns baffles transformers volume controls and accessories Also be sure to check our web site www jwd com for additional manufacturers products that we distribute PURCHASE INFORMATION FOR YOUR RECORDS SERIAL NUMBER PURCHASE DATE INSTALLATION DATE INSTALLED BY PURCHASED FROM ADDRESS CITY amp STATE TELEPHONE NUMBER NAME
15. llas Texas 75371 0219 Sales 800 527 5705 Fax 800 388 9106 Corp 214 651 7341 Fax 214 939 0328 sales jwd com e www jwd com FEN The Mark of the Professional Mt d of sound service P un UD Vill MASTER SERIES BLOCK DIAGRAM ii 2 ES PLINE MIC TRIM Bo fe EA DA 120M E E I A Lalas i INPUT MUTE SEND Z o com 3E gt ma R m lt lw u TO MUTE REV e ol 7 1 Q3 Hor oe r 1 i R RELAY He up 2 T MANNTMC rv i 1 l b l i g 3 pas i i vox SENSE LOU BACANCE Vo 8 E H 24V 7 4 musco SS A z i RRMOTE a i MUTE md UNBALANCE i 4 AAN I 1 1 1 i EW N Arco ur f VOX SENTS MUTE SEND CONTROL lt vcc
16. nals to mono output of amplifier 22 Input Trim Control Recessed variable resistor for adjusting source signal integrity to pre amp stage 23 Six Control Switch Bank 1 Up RCA Down XLR TERM 2 Up CD DVD Down AUX 3 Up TERM Down XLR 4 Up MIC Down LINE 5 Up Phantom Power 24 VDC Down Off 6 Up Off Down High Pass Filter On 24 MIC LINE BALANCED level input Removable Phoenix Connector 25 MIC LINE BALANCED level input XLR Female 26 Seven Control Switch Bank 1 Up RCA Down XLR TERM 2 Up CD DVD Down AUX 3 Up TERM Down XLR 4 Up MIC Down LINE 5 Up Phantom Power 24 VDC Down Off 6 Up Off Down High Pass Filter On 7 Up MUTE SEND Down OFF A WARNING Amplifier must be powered off before changes are made to Switch Banks 6 NEW TECHNOLOGY 4 gt OLD RELIABILITY y r W Dauis amp Company e 3030 Canton Street PO Box 710219 Dallas Texas 75371 0219 Sales 800 527 5705 Fax 800 388 9106 Corp 214 651 7341 e Fax 214 939 0328 sales jwd com www jwd com y f 42 y The Mark of the Professional wired VI SETTINGS FOR ADDITIONAL FEATURES TELEPHONE VOX MUTING The Telephone Page Input 3 will mute inputs one through six This is a default feature of the M Series and cannot be modified Adjust the sensitivity of the VOX mute using a mini blade screwdriver to access the recessed variable control TEL VOX SENS 6 The transformer coupled telephone input terminals will accept either a bala
17. nced 3 Wire or unbalanced 2 Wire line direct from the telephone page port out talk battery without ring It also accepts a TEL PAGE output from a digital phone system Switch G Sleeve COM Ring HOT Tip A 600 shielded balanced input transformer is used to aid in the rejection of RF and EFI ACTIVATION OF MICROPHONE 1 VOX MUTING To activate MIC 1 VOX muting of modules two thru six simply move switch number 7 up to Mute Send 26 Adjust the sensitivity of the VOX mute using a mini blade screwdriver to access the recessed variable control MIC 1 VOX SENS 6 This works in conjunction with the TRIM control 22 a recessed variable input level control Muting issues may be experienced with certain sources like wireless micro phone receivers For these situations use the Remote Mute terminal input 5 Simply add an external switch to mute modules two through six WARNING The following changes should be made only by a quali AN fic technician to avoid the risk of electrical shock and of voiding the warranty due to static electricity The unit must be unplugged ACTIVATION OF THE SystemOverRide INPUT TO BECOME A PRIORITY INPUT To activate the SOR to become a priority input remove the cover to gain access to the board level jumper Facing the back of the amplifier the jumper is located on the back left hand side T e cu LAM of the circuit board It is numbered JP700 See PR re e Figure 3 To activate move jumper to short the EN
18. s 800 527 5705 Fax 800 388 9106 Corp 214 651 7341 Fax 214 939 0328 sales jwd com www jwd com The Mark of the Professional amp eas T Ill OPERATING SUMMARY ATE The JWD Master Series of monaural amplifiers provide the combination of interface signal control and extended mixer capacity required by professional audio system integration In addition to traditional commercial sound applications such as paging and background music the Master Series extends the scope of capabilities to include integration with telephone communications audio visual security sound masking and the analog output of digital devices that previously have been available only in more complex modular amplifiers All features are inclusive without requiring additional accessories or modifications The front panel has nine controls six volume controls plus master treble and bass and eleven LEDs monitoring the presence of a signal on the six volume controls plus the status of the Tele phone SystemOverRide Signal Out Peak and Power circuits Each of the six volume controls attenuate one of the six dip switch modules located on the back panel In addition each microphone input has a related recessed Trim Control located on the back panel that can adjust any selected MIC input s signal level to the front level control especially useful when using consumer type equipment that does not have an adjustable signal control The back panel contains six dip switc
19. sking applications Music on Hold Input Paging with VOX muting is accomplished either from the MIC input on Module 1 or through the telephone input This feature is particularly desirable in installations such as hospitals airports and auto dealerships where paging may be required from multiple locations VOX muting of modules 2 thru 6 is available using MIC 1 A wide range of background music and audio visual programming applications are supported through the RCA type inputs which can easily be switched to CD DVD or AUX level located on each of the six modules For applications requiring recording of program material a special REC OUT jack is available that is located on the back panel System expansions requiring greater power are accommodated through the BOOSTER OUT jack which allows the signal from the Master Series amplifier to be connected to the aux input of an additional amplifier An equalizer or other signal modifying devices may be easily inserted using the PRE OUT and PWR IN jacks This feature is especially useful when equalizing a difficult acoustical or reverberant room The Master volume control permits overall attenuation of the six modules Bass and Treble controls allow equalization of the voice and music signals A 400Hz high pass filter circuit is included to help protect the phenolic diaphragms used in paging horns from excursion damage caused by low frequencies Input to output comparator thermal and
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