McIntosh MC-250 User's Manual
Contents
1. The shielded cable from the program source is plugged into the right jack The INPUT switch must be in the MONO position and the OUTPUT properly connected for mono loudspeaker operation or dis tortion and loss of power may result INPUT STEREO OR TWIN AMPLIFIERS For stereo or twin channel operation it is not neces sary to use the same impedance loudspeaker on each output Simply connect each channel for the impedance desired SPEAKERS Speakers are connected at the barrier strips marked OUTPUT on the sloped panel of the amplifier Use lamp cord bell wire or wire with similar type of insulation to connect the speakers to the amplifier For the normally short distances of under 50 feet be tween the amplifier and speaker 18 wire or larger can be used For distances over 50 feet between the amplifier and speaker use larger wire The loudspeaker impedance is usually identified on the loudspeaker itself Connect one of the leads from the left loudspeaker to the screw marked COM on the LEFT OUTPUT barrier strip Connect the other lead from the left loudspeaker to the screw marked with the number corresponding to the speaker imped ance on the LEFT OUTPUT barrier strip Connect one of the leads from the right loudspeaker to the screw marked COM on the RIGHT OUTPUT barrier strip Connect the other lead from the right loudspeaker to the screw marked with the number corresponding to the speaker impedance on the RIGHT OUTPUT barrier str2. RIGHT INPUT un til itis equally as loud as the left channel The system is now balanced for loudness and provides the great est range of operation and loudness change when using the volume control on the source equipment NOW SIT BACK AND ENJOY YOUR MCINTOSH MONO e RIGHT 7 MONO GAIN La C TT a 20 INPUTS g Performance Limits and Ratings PERFORMANCE GUARANTEE Performance Limits are the maximum deviation from perfection permitted for a Mclntosh instrument We promise you that the MC 250 you buy must be capable of performance at or exceeding these limits or you get your money back Mcintosh is the only manufacturer that makes this guarantee PERFORMANCE McIntosh audio power ratings are in accordance with the Federal Trade Commission Regulation of Novem ber 4 1974 concerning power output claims for ampli fiers used in home entertainment products POWER OUTPUT STEREO o 50 watts minimum sine wave continuous average power output per channel both channels operating into 4 ohms 8 ohms or 16 ohms load impedance which 15 14 1 volts RMS across 4 ohms 20 0 volts RMS across 8 ohms 28 3 volts RMS across 16 ohms MONO 100 watts minimum sine wave continuous average power output operating into 2 ohms 4 ohms or 8 ohms load impedance which is 14 1 volts RMS across 2 ohms 20 0 volts RMS across 4 ohms 28 3 volts RMS across 8 ohms OUTPUT LOAD IMPEDANCE STEREO 4 ohms 8 ohms or 16 ohm
3. EE YEAR SERVICE CONTRACT is included with this manual The SERVICE CONTRACT is issued to you as For your protection Mcintosh selects only Your completely filled in application for a To receive the SERVICE CONTRACT all in CONTENTS SERVICE CONTRACT INSTALLATION HOW TO CONNECT CONTROL PANEL INFORMATION LISTENING TO YOUR STEREO SYSTEM PERFORMANCE LIMITS AND RATINGS PEFORMANCE CHARTS TECHNICAL DESCRIPTION BLOCK DIAGRAM N O o A A N T SH SL HERR vies ER Lue ur tt ET a ee Le Fr Mat es es 7 ene pene um rnit Tues or mishandling is not covered by the SERV ICE CONTRACT the original purchaser To protect you from misrepresentation this contract cannot be transferred to a second owner dealers who have technical competence to guide purchasers fairly and provide service when necessary To receive the SERVICE CONTRACT your purchase must be made from a Mcintosh franchised dealer SERVICE CONTRACT must be postmarked within 30 days of the date of purchase of the instrument formation on the application must be filled in The SERVICE CONTRACT will be issued when the completely filled in application is received at Mcintosh Laboratory Incor porated in Binghamton New York SS a ln re Adequate ventilation extends the trouble free life of electrical instruments I
4. Mintosh 250 THE McINTOSH MC 250 STEREO SOLID STATE POWER AMPLIFIER Reading Time 20 Minutes Price 1 25 Your MC 250 Stereo Amplifier will give you many years of pleasant and satisfactory performance If you have any questions please contact CUSTOMER SERVICE McIntosh Laboratory Inc 2 Chambers Street Binghamton New York 13903 Phone 607 723 3512 WARNING TO PREVENT FIRE OR SHOCK HAZARD DO NOT EXPOSE THIS UNIT TO RAIN OR MOISTURE Take Advantage of 3 years of FREE Service Fill in the Application NOW The terms of the contract are 1 Mcintosh will provide all parts materials and labor needed to return the measured perform ance of the instrument to the original per formance limits free of any charge The SERVICE CONTRACT does not cover any ship ping costs to and from the authorized service agency or the factory 2 Any Mcintosh authorized service agency will repair all Mcintosh instruments at normal service rates To receivethe free service under the terms of the SERVICE CONTRACT the SERVICE CONTRACT CERTIFICATE must ac company the instrument when taken to the service agency 3 Always have service done by Melntosh Sy authorized service agency If the instrument 27771 is modified or damaged as a result of un authorized repair the SERVICE CONTRACT will be cancelled Damage by improper use Copyright 1970 by Mclntosh Laboratory Inc An application for a FREE THR
5. ctions for monophonic operation Connect one speaker to the lf the screw marked Speaker LEFT COM impedance and the other Connect IS to wire between 2 ohms LEFT 4 LEFT 4 and RIGHT 4 4 ohms LEFT 8 LEFT 8 and RIGHT 8 8 ohms LEFT 16 LEFT 16 and RIGHT 16 For constant voltage 25 volts LEFT 16 LEFT 16 and RIGHT 16 When connected as above the MC 250 operates as a 100 watt per channel monophonic amplifier STEREO OUTPUT CONNECTING TO THE OCTAL SOCKET he octal socket marked OUTPUT can be used AMPLIFIER AT LIME oun rris am ih ie per AU LINE id N 7 OOO Wintosh sat maa QUIFUTA tm for all of the output impedances and voltages Con nections are made in the following fashion oolder the left Solder the right If the channel leads channel leads impedance is between between 4 ohms Pin 1 and 2 Pin 5 and 6 8 ohms Pin 1 and 3 Pin 5 and 7 16 ohms Pin 1 and 4 Pin 5 and 8 For constant voltage 25 volts Pin 1 and 4 Pin 5 and 8 When connected as outlined the MC 250 operates as a 50 watt per channel stereo amplifier MONOPHONIC OUTPUT CONNECTING TO THE OCTAL SOCKET If the Solder the leads impedance is CONNECT to 2 ohms 2 and 6 1 and 2 4 ohms 3 and 7 1 and 3 8 ohms 4 and 8 1 and 4 25 volts 4 and 8 1 and 4 When connected as outlined the MC 250 operates as a 100 watt monophonic amplifier AC POWER The MC 250 operates on 117 to 130 v
6. ge amplifier The voltage amplifier is followed by two driver transistors The output section is arranged as a series push pull amplifier The power transistors used in the out put section of your MC 250 are selected for their high power dissipation capability wide frequency re sponse and large safe operating area In addition each power transistor is given four separate tests before it is put in your MC 250 This additional test ing makes sure your MC 250 will deliver its rated power from 20 Hz to 20 000 Hz with low distortion and complete reliability The power transistors are mounted on oversized anodized heat sinks The heat sinks assure that un der normal operation the transistors will operate at a low temperature If temperatures increase due to a shorted speaker or restricted ventilation an auto matic temperature sensing device turns off the MC 250 The device operates automatically at a preset temperature The MC 250 will turn on again when the temperature has returned to normal limits This ad ditional feature gives your MC 250 complete relia bility under the most extreme operating conditions The output stages are matched to the load by the Mcintosh autoformer The Mcintosh autoformer is carefully wound using Mclntosh trifilar winding and interleaving techniques Trifilar winding and inter leaving gives the autoformers exceptional band width The autoformers properly match the power transistors to 4 8 and 16 ohm
7. h 17 94 cm 10 8 inches wide 26 99 cm 15 8 inches deep 39 69 cm CHASSIS Chrome and black WEIGHT 36 pounds 16 33 kg net 40 pounds 18 14 kg in ship ing carton 001 a 63 Ex E SoS L a lt I o c ud Typica 9 F4 lt 55 5 SILVA INS TVATOOS3 NI LLL QC MEE DN INdLNO H3AO d NOILYOLSIO NOLLYINGOWUSLNI Z1H3H NI AONSND AY 4 000001 Dod 01 DUCI anat MIET INTEL TIT NO uso 1519 NOLLV1nOONHS3LNI 39V ENJOH3d AOUN3nO03H4 s INdLNO Y3MOd Oe SA lt lt ZH 0g 39vHJAV NI HIMO pep F y T IH INdLNO Ha3MOd 5 NOILHOLSIG JINOWHYVH HH 3 Ka LO NI Ed LOO NOILYOISIO OINDINHYH 395v UN3 2H3d Technical Description A two stage preamplifier with three transistors in each channel increases the input voltage 16 dB There are 13 transistors in each power amplifier section The two stage preamplifier is fed to a pair of matched transistors arranged as an emitter coupled amplifier with two inputs and one output The signal from the preamplifier section connects to one of these inputs Both AC and DC negative feedback are applied to the other input This large quantity of feedback is used to reduce noise and distortion The signal is then fed to a volta
8. ip The only adverse effect on the operation of a Mc Intosh amplifier when it is improperly matched is a reduction in the amount of distortion free power available to the loudspeaker Close impedance matching is desirable for maximum distortion free power SPEAKER CONNECTIONS Use this table to determine proper speaker con nection Connect the If the speaker impedance speaker leads is between between COM and 3 2 to 6 5 ohms 4 ohms 6 5 to 13 ohms 8 ohms 13 to 26 ohms 16 ohms STEREO OUTPUT CONNECTING TO BARRIERSTRIPS Use this table for stereo connections using the barrier strips Connect one Connect one left rightspeaker speaker to lead to the screw screw marked If the speaker LEFT COM RIGHT COMand impedance is other to the other to 4 ohms LEFT 4 RIGHT 4 8 ohms LEFT 8 RIGHT 8 16 ohms LEFT 16 RIGHT 16 For 25 volt line operation connect one of the left leads to the screw marked COM on the LEFT OUT PUT barrier strip The other left lead is connected to the screw marked 16 on the LEFT OUTPUT barrier Strip Connect the right leads in the same manner on the RIGHT OUTPUT barrier strip When connected as above the MC 250 operates as a 50 watt per channel stereo amplifier MONOPHONIC OUTPUT CONNECTING TO BARRIER STRIPS When the MC 250 is to operate as a monophonic amplifier the two channels are combined to produce a single 100 watt output This chart lists the proper connections and interconne
9. loads at all audio frequencies The use of the Mcintosh designed trifilar auto former makes the Mcintosh solid state amplifiers the only amplifiers that deliver FULL POWER AT ALL SPEAKER IMPEDANCES You have not been power penalized for your choice of loudspeakers when using the McIntosh MC 250 Another of the advantages of the autoformers is the 25 volt output for a constant voltage distribution system With the MC 250 several sets of speakers can be operated independently throughout your home To further insure reliability a special power output SENTRY MONITORING CIRCUIT prevents failure of the power output transistors due to excessive mis match of the output When your MC 250 operates normally the SENTRY MONITORING CIRCUIT has no effect on signals passing through the power ampli fier If the power dissipation should rise above nor mal operation the SENTRY MONITORING CIRCUIT restricts the drive to the output transistors The SENTRY MONITORING CIRCUIT acts instantaneous ly for any input signal or load combination This ar rangement assures complete circuit reliability Only McIntosh gives you this degree of protection There are three separate power supply sections One positive and one negative high current supply is used for the output stages The other positive sup ply is used for the driving amplifier stages All sup plies are full wave and use silicon rectifiers Ade quate filtering is used to assure an absolute minimum
10. of hum The power output stage filter capacitors have very high capacity which allows full power output below 20 Hz The power transformer is generous in size and runs cool even under heavy use na LAd Lo H3uvidS uU ul LI indino ox H343V3d5 1331 58 looool 179427058 1064470 ass sima 25 ELLAS pading U tte HIA hG EHTEL Erano 307116 lhalno g Fer C 3213224 NET Haller DH LE whi LEN 2 0003324 i 2 309334 indino 2 HITOS a ume ang pea arcad inne 35w14 Lag LAS 49ra MANI LHSIH ONOW 1431 Welntosh MCINTOSH LABORATORY INC 2 CHAMBERS ST BINGHAMTON N Y 13903 607 723 3512 Design subject to change without notice Printed in U S A 038 918
11. olt 50 60 Hz The amplifier will be turned on and off if its power cord is plugged in one of the auxiliary AC outlets on the program source 1 m i 7 l LOW LEVEL ur v 9 0 0 es OUTPUTS a contro Panel Information INPUT The input of the MC 250 has a two position switch to permit the amplifier to be used in any one of three ways 1 As a monophonic 100 watt amplifier 2 As twin 50 watt amplifiers used with an elec tronic crossover network or as two completely separate amplifiers 3 As a stereo amplifier used with a Mcintosh preamplifier or other high output stereo pro gram sources In either position of the input switch the input sensitivity is 0 5 volts for full rated output The input impedance is 200 000 ohms In the STEREO position each input is controlled by a GAIN control The GAIN control allows signal sources of 0 5 volt up to 30 volts to be connected without overloading the input to the amplifier The MONO position of the input switch parallels the inputs of both amplifiers When the outputs are properly connected the MC 250 becomes a 100 watt monophonic amplifier The RIGHT MONO GAIN con trol permits connecting signal sources up to 30 volts without overloading the amplifier s input To operate the MC 250 as a 100 watt monophonic amplifier the INPUT switch must be in the MONO position and the OUTPUT must be properly connected for mono ph
12. onic operation OUTPUT The two barrier terminal strips marked LEFT OUT PUT and RIGHT OUTPUT provide stereo connections for the normal speaker impedances of 4 ohms 8 ohms and 16 ohms or monophonic operation con nections for 2 ohms 4 ohms and 8 ohms The ter minal strips may also be connected for a constant voltage output of 25 volts in either stereo or mono OUTPUT Octal Socket The octal socket marked OUTPUT has stereo con nections for 4 ohms 8 ohms 16 ohms and 25 volts For monophonic operation the octal socket provides connections for 2 ohms 4 ohms 8 ohms and 25 volts AC OUTLET The auxiliary AC outlet can be used to supply power to other equipment in the system The outlet will provide a maximum of 300 watts of power The AC outlet is not fused LINE VOLTAGE The MC 250 operates on any line voltages between 117 volts and 130 volts 50 60 Hz Listening to Your stereo System SETTING THE GAIN CONTROLS To set the GAIN controls for a stereo system use a monophonic signal from the program source A monophonic signal supplies the same voltage to both channels Turn the volume control on the source equipment to the 12 o clock position half rotation Turn up the LEFT GAIN control until the loudness CIRCUIT BREAKER OUTPUT G 17 VOLTS 50 60 He AC OUTLET 50 250 WATTS 300 WATTS AN st pt in the room is about as loud as you like to listen Then turn the GAIN control on the
13. s separate ter minals are provided for each output MONO 2 ohms 4 ohms or 8 ohms separate terminals are provided for each output RATED POWER BAND 20 Hz to 20 000 Hz TOTAL HARMONIC DISTORTION STEREO 0 25 maximum harmonic distortion at any power level from 250 milliwatts to 50 waits per channel from 20 Hz to 20 000 Hz both channels operating MONO 0 25 maximum harmonic distortion at any power level from 250 milliwatts to 100 watts from 20 Hz to 20 000 Hz INTERMODULATION DISTORTION STEREO 0 25 if instantaneous peak power output is 100 watts or less per channel with both channels operating for any combination of frequencies 20 Hz to 20 000 Hz MONO 0 25 if instantaneous peak power output is 200 waits or less for any combination of frequencies 20 Hz to 20 000 Hz FREQUENCY RESPONSE at 1 watt output 20 Hz to 20 000 Hz 0 0 25 dB 10 Hz to 100 000 Hz 0 3 0 dB NOISE AND HUM 90 dB below rated output RATINGS OUTPUT VOLTAGES Stereo and Mono 25 volts for distribution lines DAMPING FACTOR 15 at 3 ohms output 38 at 8 ohms output 17 at 16 ohms output INPUT IMPEDANCE 200 00 Ohms INPUT SENSITIVITY 0 5 volt Level control provided for higher input voltage GENERAL INFORMATION POWER REQUIREMENTS 120 volts 50 60 Hz 50 watts at zero signal output 250 watts at rated output SEMICONDUCTOR COMPLEMENT 24 silicon transistors 18 silicon rectifiers and diodes MECHANICAL INFORMATION SIZE 7 1 16 inches hig
14. t is gen erally found that each 10 centigrade 18 F rise in temperature reduces the life of elec trical insulation by one half Adequate ven tilation is an inexpensive and effective means of preventing insulation breakdown that re sults from unnecessarily high operating tem peratures The direct benefit of adequate ventilation is longer trouble free life The suggested minimum space for mount ing the MC 250 is 18 inches long X 8 inches wide X 11 inches high Always allow for air flow by either ventilation holes or space next to the bottom of the amplifier and a means for the warm air to escape at the top It is recommended that the MC 250 be mounted in a normal or horizontal position However with adequate ventilation the ampli fier can be mounted in any position except upside down If the amplifier is to be installed on a vertical surface it is recommended that the autoformers be on the down side This position permit greater air flow around the transistors and component parts thereby ex tending the trouble free life of the amplifier INPUT STEREO The shielded cable from the left output of the Mc Intosh preamplifier is plugged into the left jack The shielded cable from the right output of the Mcintosh preamplifier is plugged into the right jack The INPUT switch must be in the STEREO position and the OUT PUT properly connected to the stereo loudspeakers or distortion and loss of power may result INPUT MONO
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