McIntosh ML4M Loudspeaker System Service Information.pdf

ltMntosb ML 4M LOUDSPEAKER SYSTEM SPECIFICATIONS SPEAKER SIZE Woofers four 12 dia. frame size (10 dia. radiators) Low mid-range 8 dia. frame size (5 dia. radiator) Mid mid-ranges two 1-1/2 dia. dome radiators High mid-ranges two 1-1/2 dia. dome radiators Tweeters two 1-5/8 dia. coaxial super radiators CROSSOVER FREQUENCIES 250Hz, 1.5kHz, 3kHz, & 7kHz IMPEDANCE 8q Nornina1 POWER HANDLING: Sine wave steady state SINE WAVE POWER LIMIT IN WATTS FREQUENCY IN Hz Avoid operating the speaker system with sustained sine wave signals at power levels greater than the indicated limits. Permanent damage may result. POWER HANDLING: Program Material High energy peaks normal to orchestral music are easily and faithfully reproduced by the speaker system. These peaks are of relatively short duration and do not produce the heating effect caused by sustained tone operation. The ML-4 speaker system will handle up to 300 watts of orchestral music program material. Care must be taken, however, to use a power amplifier that has an adequate power rating. If a low power amplifier is used, the loudest passages may be clipped by the amplifier. This clipping will cause the speaker to sound distorted. The large harmonic content of a badly clipped signal can cause excessive heating and re sulting damage to the high frequency speaker elements and crossover network. OUTPUT LEVEL In a reverberant room the system will nominally produce an 89dB sound pressure level when driven at a one watt level referred to 8fi. SPEAKER LOCATION SCHEMATIC NOTES 1. 1n some units C4 is 3nF. 2. 1n some units C3 is 5pF. 3. 1 n some units C2 i s two 50|jF capac i tors i n series. 4. In units with Ser No. .1 when rep 1ac i a 1 No ing 8 s Below L1E189 R2 i 1oudspeaker. is 10o (Part #139-089). Refer to ML-4C/ML-4M S. B. 5. In units with Ser Refer to ML-4C/ML i a i No 1 -4M S. s. Below L2E3I8 LI B. No. 2. is 8mH (Part #122-119) and C 1 is 150|uF (Part #066-194) CROSSOVER NETWORK LS6 o 00 cn m CO CO CO CO CO CO _i _l _l LS5 ASSEMBLY 044-223 NOTE 7 SERVICE NOTES Speaker element failure can be quickly located by using FM hiss at a low level. Listen at each speaker to verify if all the speakers are at least working. A low power (1-5 watt) sine wave sweep 20-20kHz can be used as a quick check for distortion. A speaker element with obvious distor tion must be replaced. Short circuiting individual domes may help to locate a defective one. To determine if the speaker element is dead, remove the speaker and momentarily connect a 1.5 to 6V battery across the terminals. If no sound is heard, the speaker element must be replaced. The crossover network must be inspected when burned out speaker elements are replaced. The network must also be inspected if a speaker element produces sound with the battery test but does not play when connected in the system. The back must be removed to get to the crossover, check for burned resistors, bad connections, broken wires, etc. When a system has been driven excessively hard by a clipped amplifier for long periods of time, the 8 and/or dome mid-ranges may appear to have weak or no output. In addition to burned out speaker elements, the 25nF, 4.7pF, or 3.3pF capacitors may also be damaged. This will be evident if a new 8 or new dome mid-ranges have been installed and also appear to have weak or no output. Use only McIntosh replacement capacitors. These have been specially selected for low ESR. Use RTV silicone rubber under replacement parts when mounting on the crossover board. In addition to the solder connections. This will insure a vibration free bond to the board. The solid colored wire (other than black) always goes to the red marked terminal on the speaker. This is the positive terminal. If the polarity of a speaker is unknown, momentarily connect a 1.5 to 6V battery to the terminals. When the cone moves away from the magnet, it means the + terminal of the battery is connected to the + terminal of the speaker. When installing speakers in the cabinet, care must be taken to insure a tight air seal. Re place the black caulking material or foam gasket if necessary. Mortite caulking compound or equivalent could be substituted but care must be taken that it will not be visible after the part is installed. If a woofer screw strips out in the wood of the cabinet, the speaker can be rotated and new mounting holes drilled. After the system is reassembled, it must be checked for air leaks. This can be done by putting a 20Hz sine wave into the system at 50 watts (20V). By listening around the speakers closely for hissing sounds, areas can be located that must be sealed. The system must also be swept from 20Hz to 250Hz at 50 watts to insure there are no vibrations due to wires hitting the woofer core, etc. All defective parts must be packed well and returned to the McIntosh Laboratory Loudspeaker Division. REPLACEMENT PARTS All parts not listed are common items obtain able from radio parts jobbers. Replacement parts may be obtained when ordered by PART NUMBER from: McIntosh Laboratory, Inc. Customer Service Department 2 Chambers Street Binghamton, New York 13903 (telephone 607-723-3512) CAPACITORS S ymbo1 Number Description Part Number MISCELLANEOUS ITEMS C 1 Elect. 50pF 100V 066-192 Terminal Red 084-086 C2 Elect. 25pF 100 V 066-189 Terminal Black 084-087 C3 Mylar 4.7pF 250V 064-107 Shipping Carton 033-169 C4 Mylar 3.3pF 100V 064-117 Grille Cloth 031-002 C5 Mylar IpF 250V 064-104 Front Panel Assy. 044-362 Speaker Gasket 12 Woofer 094-092 CHOKES Speaker Gasket 2-1/4 Tweeter 094-096 L2 Choke 3mH 122-120 Speaker Gasket l-)/2Dome 094-100 L3 Choke . 3mH 122-164 Speaker Gasket 8 Midrange 094-094 L4 Choke 6mH 122-168 Network Gasket 094-106 L5 Choke . 3mH 122-164 L6 Choke . 2mH 122-163 LOUDSPEAKERS LSI ,2 12 Woofer 036-001 LS3,4 12 Woofer 036-001 LS5 8 Midrange 036-025 LS6,7 1-1/2 Dome Midrange 036-016 LS8,9 1-1/2 1 Dome Midrange 036-017 LS10,1 1 2-1/4 Tweeter 036-012 RESISTORS R2 Wirewound 7.5ft 10W 139-090 R3 W i rewound 1 2ft 1 ow 139-088 R4,5 Wirewound 2n low 139-085 R6 Wirewound 6n low 139-087 R7 Wirewound 2ft low 139-085 R8 Wirewound 3ft low 139-083 nMntostt McIntosh loudspeaker division 2 CHAMBERS ST., BINGHAMTON, N.Y. 13903 SERVICE BULLETIN REPLACEMENT OF 8 LOUDSPEAKER 036-002 MODEL: ML-AC and ML-AM Loudspeakers. PURPOSE OF MODIFICATION: To maintain the same acoustic output. WHAT UNITS ARE AFFECTED: ML-AC Serial No. L1E001 through L1 El 89 - ML-AM Serial No. L1F001 through LIFO52. WHEN MODIFICATION SHOULD BE MADE: When replacing defective 036-002 8 loudspeaker. MclNTOSH MODIFICATION KIT: No kit available. PARTS REQUIRED: QUANTITY 1 1 PROCEDURE: Step 1 Remove rear panel. Step 2 Locate 10ft, 10 watt resistor in series with the 8 loudspeaker. Remove and replace with 7.5ft, 10 watt resistor. Step 3 Replace rear panel. (ove r) McIntosh Laboratory incorporated 2 Chambers Street Binghamton, New York 13903 Phone: Area Code 607-723-3512 PART NUMBER DESCRIPTION 139-090 Wirewound Resistor: 7.5ft, 10W 036-025 8 Loudspeaker ML-4C/4M S.B. No. 2 SERVICE BULLETIN REDUCE UPPER BASS RESPONSE MODEL: ML-4C and ML-4M Loudspeakers. PURPOSE OF MODIFICATION: To provide smoother response in some 1istening rooms. WHAT UNITS ARE AFFECTED: ML-4C Serial No. L2E318 & Above. ML-4M Serial No. L1 FI 71 & Above. WHEN MODIFICATION SHOULD BE MADE: When customer complains about excessive upper bass. MclNTOSH MODIFICATION KIT: No kit available. PARTS REQUIRED: QUANT ITY 1 1 2 PART NUMBER 122-116 066-188 101-040 DESCRIPTION Choke: 33mH Capacitor: 50pF Wood Screws: #6 x 1/2 PROCEDURE: Step 1 Step 2 (Refer to Fig . 1 ) Remove rear panel of speaker cabinet. Locate 8mH choke (the largest coil with an iron core) and the 150pF capacitor. These parts are to be removed and replaced with the 33mH choke and 50pF capacitor. Step 3 Mount the 33mH choke as illustrated. NOTE: In some early units the terminal connections may not be as illustrated. Proceed in the same manner as described. (over) McIntosh Laboratory Incorporated 2 Chambers Street Binghamton, New York 13903 Phone: Area Code 607-723-3512 FIG. 1 REPLACE WITH 50 jjF CAPACITOR I2L0UDSPEAKERS 038-589