McIntosh MC-2300 User's Manual
Contents
1. LEFT GAIN The left gain control is used to control gain or volume of the left channel Clockwise rotation increases gain RIGHT MONO GAIN In stereo the RIGHT MONO GAIN control deter mines the gain or volume of the right channel only Clockwise rotation increases gain If the MC 2300 is connected as a monophonic or single channel ampli fier the gain or volume is controlled by the RIGHT MONO GAIN control Both controls have a standard volume control taper The numerals around the controls are provided for reference They do not represent relative output versus rotation METER RANGE The meter switch has four positions The first posi tion is OFF With switch in the OFF position there is no indication on the meters 0 In this position of the meter range switch the amplifier will deliver 300 watts when the meter in dicates 3 dB with meter indication of 0 the amplifier delivers 150 watts with a meter indication of 3 dB the amplifier delivers 75 watts 10 In this position of the meter range switch the amplifier will deliver 15 watts output when the meter indicates 0 20 In this position of the meter range switch the amplifier will deliver 1 5 watt when the meter indicates 0 Two meters monitor and indicate the output power in each channel The meters indicate peak power out put of the monitored channel To assure more accu rate indications of peak power Mcintosh s peak lock ing circuits stretch2. combined to produce output up to 600 watts The output must be tied together at the appropriate load impedance tap In connecting a load to the MC 2300 for single channel operation connect the common side of the load to the LEFT CHANNEL OUTPUT ter minal marked COM the other lead as below lf the speaker The hot side or load of the line Is Impedance Is connected to Connect a jumper wire between 0 25 ohms Left 0 5 Left 0 5 and Right 0 5 0 5 ohms Left 1 Left 1 and Right 1 2 ohms Left 4 Left 4 and Right 4 4 ohms Left 8 Left 8 and Right 8 8 ohms Left16 Left 16 and Right 16 If the load impedance is between any of the above figures seclect the best impedance match from this chart Load Impedance Dear pence Connect to in ohms Connect to 0 4 to 0 9 0 5 3 6 to 7 2 4 0 9 to 1 8 1 7 2 to 14 4 8 1 8 to 3 6 2 14 4 to 28 16 WIRE GAUGE 22 20 18 RESISTANCE OF WIRE OHMS For monophonic constant voltage line operation The hot side a jumper If th tput f the load voltage connected to wire between 25 volts Left 2 Left 2 and Right 2 70 volts Left 16 Left 16 and Right 16 Make all speaker connections at the amplifier only For multiple speaker operation parallel the leads from the speakers to the amplifier Should the MODE SWITCH be left in the STEREO position and the output transformers be strapped to a monophonic load one channel will attempt to drive the other and cause circulating currents and ove
3. to lose its charge by the RC time constant of C201 R209 For that amount of time a positive charge is supplied to the base of Q201 causing it to conduct for a longer length of time The RC combination R215 C203 act as a meter upswing accelerator while the RC combination R209 C201 act as a pulse or time stretching aid Variable resistor R213 is used to ad just the meter to read exactly 3 at 300 watts RMS All components of the meter circuit have been selected and designed to have maximum flat sponse at the frequency extremes A reading of a given power is correct regardless of the frequency of the signal The MC 2300 contains two independent meters and meter circuits Both meter circuits oper ate the same and are completely independent except for meter range setting The meter range switch does not alter the sensitivity of the meter circuit but attenu ates by the correct ratio the amount of input signal to the meter circuit POWER SUPPLIES To deliver rated power at frequency extremes de sign of a power amplifier supply must have good regulation and ample reserve At lower frequencies the power supply capacitors must be of sufficient size to deliver full voltage cycle after cycle with no increase in ripple At higher frequencies power tran sistors require more power The power supply must be able to furnish the additional power without sacri ficing regulation or overheating In all cases the power furni
4. cm including connectors Clearance in front of mounting panel in cluding knobs 2 inches 5 08 cm FINISH Front panel is anodized gold and black Chassis is black baked enamel MOUNTING Standard 19 48 26 cm rack mounting WEIGHT 128 pounds 58 06 kg net 143 pounds 64 86 kg in shipping carton SPECIAL FEATURES The amplifier is completely stable when connected to any loudspeaker system and to any reactive loads The MC 2300 has special circuits to prevent damage by short circuit or open circuit of the output loads or by any amount of out put impedance mis match Thermal cutouts are mounted on the output tran sistor heat sinks to provide protection in the event of inadequate ventilation Typical Performance Charts E e 2 a I 2 POWER OUTPUT IN WATTS PERCENT INTERMODULATION DISTORTION 400 360 320 280 H 240 200 160 120 HARMONIC DISTORTION vs POWER OUTPUT 5 55225 POWER OUTPUT IN AVERAGE WATTS POWER BANDWIDTH FREQUENCY HERTZ INTERMODULATION DISTORTION SU OO A ___ _ __ IN POWER OUTPUT IN EQUIVALENT AVERAGE WATTS 10 Technical Description Each channel of the MC 2300 can be divided into five different sections These sec
5. money back Mcintosh is the only POWER OUTPUT STEREO 300 watts continuous both channels op erating which is 12 2 volts RMS across 0 5 ohm 17 3 volts RMS across 1 ohm 24 5 volts RMS across 2 ohms 34 6 volts RMS across 4 ohms 49 0 volts RMS across 8 ohms 69 3 volts RMS across 16 ohms MONO 600 watts continuous which is 12 2 volts RMS across 0 25 ohm 17 3 volts RMS across 0 5 ohm 24 5 volts RMS across 1 ohm 36 6 volts RMS across 2 ohms 49 0 volts RMS across 4 ohms 69 3 volts RMS across 8 ohms HARMONIC DISTORTION Stereo Less than 0 25 at 300 watts output from 20 Hz to 20 000 Hz both channels operating Typical per formance is less than 0 1 at rated power Distor tion decreases as output power is reduced Mono Less than 0 25 at 600 watts output from 20 Hz to 20 000 Hz Typical performance is less than 0 1 at rated power Distortion decreases as output power is reduced INTERMODULATION DISTORTION Stereo Less than 0 25 if instantaneous peak power is 600 watts or less per channel with both channels operating for any combination of frequencies 20 Hz to 20 000 Hz Mono Less than 0 25 if instantaneous peak power is 1200 watts or less for any combination of fre quencies 20 Hz to 20 000 Hz FREQUENCY RANGE Stereo 20 Hz to 20 000 Hz 0 0 5 dB at rated power 1 4 8 or 16 ohms 20 Hz to 20 000 Hz 0 1 0 dB at rated power 0 5 and 2 ohms 12 Hz to 35 000 Hz 0 1 5 dB at one half rated pow
6. the peak reading of rapid chang ing information long enough to give adequate visual perception Ordinary meters lack the capability of in dicating the short interval of power in a sound wave The mass of the meter movement is too great to re spond to the nearly instantaneous changes in music program material Mcintosh has developed circuits that permit the meters of the MC 2300 to respond to the short interval power in a sound wave to an accu racy of 98 Monitoring of the output power is done at the pri mary or input of the autoformer resulting in true power readings regardless of output impedance selected The graph represents the relationship between the meter reading and power output for all three meter ranges g POWER The power switch turns the MC 2300 or off If you wish to control the on off operation of the ampli fier remotely use a control relay in series with the power line and leave the power switch in the ON position Do not plug the MC 2300 into any of the auxiliary AC power outlets of the preamplifier or other associated equipment unless that equipment has power capacity for handling 1400 watts 14 am peres Performance Limits PERFORMANCE GUARANTEE Performance Limits are the maximum deviation from perfection permitted for a Mcintosh instrument We promise you that the MC 2300 you buy must be capable of performance at or exceeding these limits or you qet your
7. 7 el E RIGHT RIGHT 1855 15 enor METER LIGHTS BlockDiagram LEVELI 104110 LEIEL MILIMS JONVE eso inano 9 45 0 77 19 se lo aonya 0 EINSOIOLNY 114110 WO 550 anano 2 9 acs eat o 104100 O 3138 332180 VOLINOW 104100 Alam 31114 414405 HIMOA 3114 114405 HOLIMS 440 NO 38 15 104100 8 55 12 IN OV amp O EEN 1437 43M04 O VIWIOISNVUL inant any ONOW IHOIY 1048 onow 4IMO4 714914 39 15 8 55712 amp 699 amp amp O 43v80333 XUOMIIN 1180334 038315 AJOMLIN 10v90333 39 15 114110 8 55 12 9 22 O 83110841802 El 1331 any awy any 1431 4 m 39 15 104100 55912 Mentosh MCINTOSH LABORATORY INC 2 CHAMBERS ST BINGHAMTON 13903 607 723 3512 Design subject to change without notice Printed in U S A 038 662
8. L INFORMATION 8 PERFORMANCE LIMITS 9 TYPICAL PERFORMANCE CHARTS 10 Take Advantage of 3 years TECHNICAL DESCRIPTION 11 of FREE Factory Service BLOCK DIAGRAM 16 Fill in the Application NOW GUARANTEE Mcintosh Laboratory Incorporated guarantees this Instrument to be capable of performance as adver tised We also guarantee the mechanical and elec trical workmanship and components to be free of defects for a period of 90 days from date of pur chase If such defects occur Mcintosh Laboratory An application for a FREE THREE YEAR FACTORY SERVICE CONTRACT is included with this manual The terms of the contract are For Three Years from date of purchase 1 Mcintosh will provide all parts materials and labor needed to return the measured performance of the instrument to the original performance limits free of any charge The SERVICE CON TRACT does not cover any shipping costs to and from the authorized service agency or the factory 2 Any Mcintosh authorized service agency will re pair all Mcintosh instruments at normal service rates To receive the free service under the terms of the SERVICE CONTRACT the SERVICE CON TRACT CERTIFICATE must accompany the instru ment when taken to the service agency Always have service done by a Mcintosh author ized service agency If the instrument is modified or damaged as a result of unauthorized repair the SERVICE CONTRACT will be cancelled Damage by imp
9. Meintosh MC 2300 THE McINTOSH MC 2300 SOLID STATE STEREO POWER AMPLIFIER 2300 00 3 0 0 STEREO POWER AMPLIF Price 1 25 The Mcintosh 2300 is a high quality ex tremely high power solid state stereo ampli fier Because of the high power available it is necessary to emphasize some prudent and safe operating conditions 1 Never connect or disconnect inputs or outputs while the amplifier is turned on Loudspeakers can be damaged or de stroyed by the high power available from the instrument Never operate the amplifier with the power cord plugged into an auxiliary AC power outlet on source equipment The amplifier draws near 14 amperes at full power and damage to the source equipment can occur Do not operate the instrument plugged into an ordinary extension cord Heavy duty extension cords 14 ga or heavier have adequate wire size and will not over heat Be cautious when lifting the instrument It weighs 128 pounds Make certain that what it is placed on can support the weight Your MC 2300 Stereo Power Amplifier will give you many years of pleasant and satisfactory performance If you have any questions concerning the operation or maintenance of CONTENTS GUARANTEE 1 this instrument please contact nen 8 SUS TOMER SERVICE HOW TO CONNECT 4 5 Mcintosh Laboratory Inc Stereophonic 6 New Yoik 13903 7 Phone 607 723 3512 FRONT PANE
10. capaci tor parallels R20 to increase the amount of feedback RIGHT MONO 9 INPUT at frequencies above 50 000 Hz This increased feed back reduces the noise level of the input section where the signal to noise level is more critical it also rolls off the frequency response above 50 000 Hz Resistors R9 and R10 with C5 C6 form a filter chain to filter the 21 volts used to supply the input am plifier Left and right channels operate identically The output of the left and right input amplifiers is fed to the mono stereo switch OPERATION OF MONO STEREO SWITCH If the MODE switch is in the STEREO position each input amplifier is directly connected to its spective power amplifier In the MONO position the output of the right channel input amplifier is ted to both left and right power amplifiers the LEFT INPUT is disconnected For stereo or twin channel opera tion the MC 2300 has two independent amplifying sections Consequently each amplifier output can be loaded with any desired impedance load For MONO operation the two power amplifier output sections are connected together for parallel operation The output load therefore must be connected to the out put of each channel strapped together in parallel Should the MODE switch be left in the STEREO position and the output transformers be strapped to a mono load one channel will attempt to drive the other and cause high circulating currents and over heating Be certain that
11. ectrical power to operate the unit the weight and the heat generated when the MC 2300 is operating The MC 2300 draws 1400 watts or about 14 am peres when operated at full power Do not use ordi nary extension cords of any type Heavy duty exten sion cords 14 ga or heavier have adequate wire size and will not overheat Plug the AC power cord directly into a wall outlet Make certain that the AC power outlet has at least 15 amperes capacity with nothing else using the circuit Do not plug the MC 2300 into an auxiliary AC power outlet on a pre amplifier or other source equipment If remote power operation is required an external relay arrangement must be made Weight of the instrument is 128 pounds Make certain that the shelf on which it is to be mounted can support that weight If it is to be vertically mounted be certain the structure is capable of sup porting the MC 2300 Adequate ventilation extends the trouble free life of electronic instruments It is generally found that each 10 centigrade 18 F rise in temperature re duces the life of electrical insulation by one half Adequate ventilation is an inexpensive and effective means of preventing insulation breakdown that re sults from unnecessarily high operating tempera tures The direct benefit of adequate ventilation is longer trouble free life Provide a source for input air and an outlet for the heated air The heat gener ated in the operation of the MC 2300 is ex
12. er Mono 20 Hz to 20 000 Hz 0 0 5 dB at rated power 0 5 2 4 or 8 ohms 20 Hz to 20 000 Hz 0 1 0 dB at rated power 0 25 and 1 0 ohms 12 Hz to 35 000 Hz 0 1 5 dB at one half rated power NOISE AND HUM 90 dB below rated output OUTPUT POWER MONITOR METER Meter is calibrated to read 3 db when ampli fier produces 300 RMS watts or 600 peak watts Meter range switch is provided to increase meter sensitivity by 10 dB or 20 dB Meter features special circuit to respond to peak values of complex input signal Calibration accuracy at 0 dB is 2 at all frequencies meter range accu racy is 5 OUTPUT IMPEDANCE Stereo 0 5 1 2 4 8 and 16 ohms Mono 0 25 0 5 1 2 4 and 8 ohms OUTPUT VOLTAGES 25 volts stereo and mono 70 volts stereo and mono DAMPING FACTOR 27 at 0 5 ohm output 50 at 1 ohm output 29 at 2 ohm output 21 at 4 ohm output 14 at 8 ohm output INPUT IMPEDANCE 200 000 ohms INPUT SENSITIVITY 0 5 volts input required to produce rated output Level control provided for input voltages up to 30 volts POWER REQUIREMENTS 120 volts 50 60 Hz 160 watts at zero signal out put 1400 watts at rated output SEMICONDUCTOR COMPLEMENT 46 Silicon transistors 22 Silicon rectifiers and diodes MECHANICAL INFORMATION SIZE Front pane measures 19 inches wide 48 26 cm by 10 inches high 26 67 cm Chassis meas ures 17 inches wide 43 18 cm by 10 inches high 25 4 cm by 17 inches deep 43 18
13. hausted from the unit by two low noise long life fans Cooling input air is drawn into the MC 2300 through the ventilation holes on the sides of the MC 2300 The air passes over the tranformers output heat sinks and transistors and is blown out the back of the instrument by the two fans It is recommended that at least 2 inches of clear space be provided on each side To permit the fans to operate best provide at least 5 inches of space at the rear of the instrument A source for input air and a means to exhaust the heated air is necessary so that the heated air does not recirculate through the MC 2300 To install the unit in a cabinet the aluminum side rails with the feet attached must be removed The rails are attached to the front panel by 8 10 32 machine screws and to each side by 4 small clips Remove both the front panel screws and the four clips from each side for cabinet mounting The open ing to fit the unit is 17 by 10 inches RACK INSTALLATION The MC 2300 may be mounted in a standard 19 rack by removing the aluminum side rails If a stand ard rack is used the screws that held the aluminum rails to the front panel are used to attach the MC 2300 to the rack When rack mounted the MC 2300 requires 10 inches of panel space Allow two inches in front of the panel for the knobs A depth of 17 inches plus ventilation space is required The MC 2300 can be slide mounted in a rack Tapped well nuts and internal struc
14. nd the output transformers be strapped to a mono phonic load one channel will attempt to drive the other and cause high circulating currents and over heating Be certain that the MC 2300 is never oper ated in the stereo mode with the outputs connected for monophonic operation OUTPUT Stereo or twin amplifier operation To connect the left speaker first check the imped ance of the speaker which is usually identified on the speaker itself or in the owner s manual Connect one lead from the common terminal of the speaker to the LEFT CHANNEL OUTPUT terminal strip screw COMmon Connect the other terminal of the speaker to the screw with the number corresponding to the speaker impedance on the LEFT CHANNEL OUTPUT terminal strip The right channel speaker is con nected in the same manner on the RIGHT CHANNEL OUTPUT terminal strip For stereo or twin channel operation it is not necessary to use the same impe dance loudspeaker on each output Connect each channel for the impedance desired When multiple speakers are to be connected to either or both outputs the combined load impedance must be calculated and the load connected to the appropriate impedance tap The following table will aid in selecting the correct impedance match Load Load impedance Connect impedance Connect in ohms to in ohms to 0 4 to 0 9 0 5 3 6 to 7 2 4 0 9 to 1 8 1 7 2 to 14 4 8 1 8 to 3 6 2 14 4 to 28 16 If a load impedance is used that is lower than the outp
15. r heating Be certain that the MC 2300 is never oper ated in the stereo mode with the outputs connected for monophonic operations AC POWER The MC 2300 is designed to operate 117 to 130 volts 50 60 Hz Do not use ordinary extension cords of any type Heavy duty extension cords 14 ga or heavier have adequate wire size and will not over heat Plug the the AC power cord directly into a wall outlet Make certain that the AC power outlet has at least 15 ampere capacity with nothing else using the circuit Do not plug the MC 2300 into an auxiliary AC power outlet on a preamplifier or other source equip ment unless it is known there is adequate current capacity If remote power operation is required an external relay arrangement must be made LENGTH IN FEET OF TWO CONDUCTOR SPEAKER WIRE STEREOPHONIC CONNECTIONS PROGRAM SOURCE o o Mdntosh AL INPUT TO 120 VAC DO NOT CONNECT LIN Se DINT PREAMPLIFIER UTLETS IF REMOTE POWER CONTROL IS NEEDED USE AN EXTERNAL RELAY LEFT SPEAKER 4 6 RIGHT SPEAKER ML 4 C MONOPHONIC CONNECTIONS PROGRAM SOURCE To 120 VAC DO NOT CONNECT LINE AC OUTLETS IF REMOTE POW CONTROL tS NEEDED USE AN EXTERNAL RELAY MODE SWITCH A ML4CLOUDSPEAKER 7 STEREO 300 300 WATT meek ROE Q Front Panel Information
16. roper use or mishandling is not covered by the SERVICE CONTRACT Copyright 1971 by Mcintosh Laboratory Inc or one of its authorized agencies wilt repair the defect at no cost to the purchaser This guarantee does not extend to components damaged by proper use nor does it extend to transportation to and from the factory or service agency The SERVICE CONTRACT issued to you as the original purchaser To protect you from misrepre sentation this contract cannot be transferred to second owner The SERVICE CONTRACT is given to purchasers who live In the 50 United States or Canada only For your protection Mcintosh selects lts dealers carefully Only one dealer in ten qualifies for a Mcintosh franchise To receive the SERVICE CONTRACT your purchase must be made from a Mcintosh franchised dealer Your completely filled In application for a SERV ICE CONTRACT must be postmarked within 30 days of the date of purchase of the instrument To receive the SERVICE CONTRACT all informa tion on the application must be filled in The SERVICE CONTRACT will be issued when the completely filled in application is received at Mcintosh Laboratory Incorporated in Binghamton New York If the application is not received at Mcintosh Laboratory only the service offered under the 90 day guarantee will apply Installation Installation of the MC 2300 requires careful thought about three important factors They are the el
17. shed to one channel should have no effect upon the performance of second channel Any effect would cause cross talk and poor channel separation In stereo use a stereo power amplifier must act as two separate amplifiers whether their power signals are common or separate This design goal is fully achieved in the MC 2300 n the Mcintosh MC 2300 two high current supplies are used Each high current supply furnishes the positive and negative forty volts required in the power output circuits The four 39 000 microfarad capaci tors store ample power over 120 joules for fre quencies in the low range The power transformer has been designed to run relatively cool at full power output Bridge rectifiers 0301 and D302 are used in both high current supplies for most efficient conver sion of power A high voltage lower current supply is designed to furnish power to the lower level and driver circuits Full wave recification and considerable filtering as sure clean signal amplification with no added hum or noise A resettable circuit breaker in the primary of the power transformer and two heat sensing switches 5302 S303 protect the amplifier against overload and or overheat gt 40 LEFT x su y FT anonn 7 20 30 80 Hz eg gt atts _ 15227 a AR R
18. t the limiter circuit is a high impedance circuit in all modes and has no effect upon the output signal If the power output exceeds the design limits the limiter circuit becomes low impedance and reduces the signal to the output transistors Both positive and negative halves of the output are monitored independently and the circuit operation is similar for both halves The amount of current flow ing through an output transistor is monitored by sens ing the voltage measured across the emitter posi tive or collector negative resistor relative to the output buss This voltage is applied to the base of the limiter transistor Q107 positive and or Q109 nega tive via the voltage dividing network R121 129 posi tive and or R123 R131 negative When the current flowing in the output attempts to exceed the design limits then the voltage at the base of the limiter tran sistors causes those transistors to conduct making a portion of the signal to the base of the driver tran sistors Q111 positive and Q113 negative to be drained off METER CIRCUIT Ordinary meters lack the capability of indicating the short interval of power in a sound wave The mass of the meter movement is too great to respond to the 14 0201 YEL osy ERE 9 LEFT age N OUTPUT METER Wan ER es 828 sates OEM sev 0203 S 1 8 nearly instantaneous changes in music program ma terial has developed circ
19. the MC 2300 is never oper ated in the stereo mode with the outputs strapped in parallel POWER AMPLIFIER At the right input channel power amplifier input two PNP transistors Q102 and Q104 are connected in a differential amplifier configuration As in the 5 RED WHT 439 11 2 RIGET OUTPUT INPUT OUTPUT SECTION P ES m 85 1 3 E 39v 12 A tapas OPERATION OF MONO STEREO SWITCH input amplifier the two signals to the differential amplifier are the normal power amplifier input sig nal and the negative feedback signal from the power amplifier output The combined output of the differ ential amplifier feeds transistor Q106 which is a common emitter Class A linear voltage amplifier The output of 0106 is directly coupled to the bases of transistors Q112 and Q118 which are NPN and PNP complementary medium power driver transistors The driver stages furnish the current required to the bases of the output transistors Q116 thru Q138 Out put transistors Q116 120 and 124 128 132 136 con trol the positive portion of the output signal while transistors Q118 122 126 130 134 138 control the negative half of the output signal These 12 output transistors work together forming a series push pull output capable of delivering extremely high currents The o
20. tions are 1 input amplifier 2 power amplifier circuit 3 limiter cir cuit 4 meter circuit and 5 power supplies INPUT AMPLIFIER 2300 will deliver rated output from an put signal of 0 5 volts The input control reduces the amount of signal into the input amplifier as the set ting is reduced By the correct setting of the control input signals on the order of 30 volts can be applied to the input of the MC 2300 without overdriving the input At the input amplifier two NPN transistors Q2 and Q4 are connected in a differential amplifier ar rangement The two inputs to the differential amplifier are the input signal and the feedback signal from the output of the input amplifier The use of a differential amplifier provides the most efficient use of larger amounts of negative feedback to maintain low noise distortion The combined output of the differen tial amplifier feeds a common emitter voltage ampli fier Q6 The output of the Q6 is coupled via a large value capacitor to the power circuit and to the feed back input of the differential amplifier A large value capacitor is used to assure good low frequency re production and to assure that no DC is coupled to the power amplifier circuits From the collector of Q6 the resistors R20 and R18 form a dividing network which determines the amount of negative feedback fed to the differential amplifier The path provides both AC and DC feedback A small trimming
21. ture bracing has been added to both sides of the MC 2300 for use with the Model CTS 116 side mounted slide assem blies manufactured by Chassis Trak Inc Indian apolis Indiana How to Connect INPUT Stereo or twin amplifier operation Use shielded cables to connect the signal from the preamplifier or signal source to the power amplifier All connection are made on the back panel of the MC 2300 For stereo operation the LEFT OUTPUT of the pre amplifier should be connected to the LEFT INPUT of the power amplifier The RIGHT OUTPUT of the pre amplifier should be connected to the RIGHT MONO input of the power amplifier In stereo or twin ampli fier operation the MODE SWITCH must be in the stereo position For twin amplifier operation a separate signal source can be connected to each input To minimize the possibility of hum the shielded leads shall be run parallel or loosely twisted to gether Locate the cables away from AC power cords Monophonic or Single Channel operation A shielded cable from the signal source is con nected to the RIGHT MONO input of the MC 2300 The MODE SWITCH on the back panel of the ampli fier must be placed in the MONO position In the MONO position the output of the right channel input amplifier is fed to both left and right power amplifiers The LEFT INPUT is disconnected Only the signal fed into the RIGHT MONO input will be amplified Should the MODE SWITCH be left in the STEREO position a
22. uits that permit the meters of the MC 2300 to respond to the short interval power in a sound wave to an accuracy of 98 Monitoring of the output power is done at the pri mary or input of the autoformer Sampling the output power in this portion of the circuit gives true power readings regardless of output impedance selected To be able to read power peaks that are sustained for such extremely short durations Mcintosh engi neers developed circuits that accelerated the up swing of the meter and caused the needle to be held at the peak reading long enough for the human eye to perceive the indication of the needle The Mc Intosh meter circuit is a dynamic peak locking meter circuit that does both things Patented Diode D203 and resistor R217 tied to the negative supply place a bias on the emitter of transitor Q201 to hold the transistor just at the threshold of conduc tion Diode D201 passes only the positive portions of the input signal to the base of Q201 charging the ca pacitor C201 Since the transistor Q201 is on the edge of conduction the slightest positive swing of in put signal causes conduction to begin The largest capacitor C203 in the emitter circuit will appear as a direct short at first to the negative supply thereby ac celerating the needle of the meter upscale At the peak of the signal the needle will stop its upswing When the meter needle reaches peak and the input signal starts a downswing the capacitor C201 starts
23. ut impedance tap then reduced power and pos sible distortion will result If a load impedance is used that is higher than the output impedance tap then neither the signal nor the amplifier will be harmed but the voltage available is limited to that stated at that tap For constant voltage line operation 25 volts 70 volts Make all speaker connections at the amplifier only For multiple speaker operation parallel the leads from the speakers to the amplifier Connect to 2 ohms Connect to 16 ohms Because of the high power available from the MC 2300 be sure to use large diameter speaker leads In all cases the leads to and from the speaker should be twin conductor or twisted together Use lamp cord bell wire or wire with similar type of insulation to connect the speakers to the ampli fier For the normally short distances of under 20 feet between the amplifier and speaker 18 wire or larger can be used For distances over 20 feet between the amplifier and speaker use larger diameter wire Se lect the correct size wire for the wire distance from the chart It is recommended that the DC resistance of the speaker leads not be over 5 of the load impedance Up to 10 can be tolerated Resistance of the leads should be computed for the length of wire both to and from the speaker or speakers Monophonic or Single Channel operation When the MC 2300 is used as a monophonic or single channel power amplifier the two channels are
24. utput transistors are mounted on oversized black anodized heat sinks Two long life quiet run ning fans draw air over the heat sinks and out the rear of the unit With all covers in place the MC 2300 will run relatively cool even under full load condi tions Resistor R112 completes the DC negative feed back path to the differential input while the resistors R112 and R106 form a voltage divider network for the AC negative feedback A high value resistor R118 in series with a high voltage power supply acts as a current source for the driver transistors 0112 and 0114 dual diode D104 and resistor R27 set the standing current for all of the output transistors to achieve Class B operation Driver transistor Q112 is physically mounted atop the dual junction diode D104 causing the junction volt age drop to decrease as the diode is heated This change in voltage causes the standing current to re main constant regardless of the operating tempera tures 13 LIMITER CIRCUIT In the power amplifier circuit the amount of signal output has a linear relationship with the input signal In the event of a short circuit or severe impedance mismatch the limiter circuit will protect the output transistors against failure The Mcintosh patented Sentry Monitoring circuit constantly monitors the out put signal and instantly reacts to prevent overload to the output transistors At signal levels up to rated out pu
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