McIntosh MC 2120 Owners Manual

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Your MC 2120 Stereo Power Amplifier will give you many years of pleasant and satisfactory performance. If you have any questions, please contact: CUSTOMER SERVICE Mclntosh 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. Contents SERVICE . . . . 1 INSTALLATION . . . . 2 HOW TO CONNECT . . . . 4 FRONT PANEL INFORMATION . . . . 8 REAR PANEL INFORMATION . . . . 10 PERFORMANCE LIMITS AND RATINGS . . . . 11 PERFORMANCE CHARTS . . . . 12 TECHNICAL DESCRIPTION . . . . 14 BLOCK DIAGRAM . . . . 16 THREE YEAR SERVICE CONTRACT An application for a FREE THREE YEAR SERVICE CONTRACT is included with this manual. The terms of the contract are: 1. Mclntosh 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 Mclntosh authorized service agency will repair all Mclntosh instruments at normal service rates. To receive the 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 a Mclntosh authorized service agency. If the instrument is modified or damaged, as a result of un- authorized repair the SERVICE CONTRACT will be cancelled. Damage by improper use or mishandling is not covered by the SERV- ICE CONTRACT. 4. The SERVICE CONTRACT is issued to you as the original purchaser. To protect you from misrepresentation this contract cannot be transferred to a second owner. 5. For your protection Mclntosh selects only 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 Mclntosh franchised dealer. 6. Your completely filled in application for a SERVICE CONTRACT must be postmarked within 30 days of the date of purchase of the instrument. 7. To receive the SERVICE CONTRACT all in- formation on the application must be filled in. The SERVICE CONTRACT will be issued when the completely filled in application is received at Mclntosh Laboratory Incorporated in Binghamton, New York. Copyright ® 1976 by Mclntosh Laboratory Inc. 1

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The input waveform and the output waveform are com- pared in an integrated circuit differential amplifier. Any differences, due to distortion of the output waveform, are converted to a control voltage. This control voltage is applied differentially to a high gam operational amplifier where it is amplified about 100 times. The amplified control volt- age is detected by a full wave bridge rectifier then enters a Schmidt trigger which is programmed to sequence the front panel indicators from NORMAL (green) to LIMIT (red] at a preset distortion level. Also built into the trigger circuit is a timing capacitor which holds the LIMIT indicator on long enough to be visible even when the duration of the overload is much shorter. The LIMIT indicator will be illumi- nated for an overload condition as short as one cycle of a signal at 20,000 Hz. The same control voltage used to activate the LIMIT indicator also actuates the POWER GUARD system. If the control voltage is greater than is needed to illuminate the LIMIT indication then the POWER GUARD begins operating. The control voltage is used to operate a light emitting diode/light dependent resistor (LDR) network. The LDR is part of an attenuator between the volume control and the input amplifier. The input to the power amplifier can be attenuated to as little as one tenth, if necessary, in order to maintain low distortion in the event of excessive input signal. The POWER GUARD circuit is activated when the rear panel switch is in the NORMAL position. POWER GUARD protection is disabled m the OUT position. The LIMIT indi- cator operates regardless of the position of the POWER GUARD switch. 15