McIntosh MC 2300 Owners Manual

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The Mclntosh MC 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. 2. 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. 3. 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. 4. Be cautious when lifting the instrument. It weighs 128 pounds. Make certain that what it is placed on can support the weight.

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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 Mclntosh 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- put 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 nearly instantaneous changes in music program ma- terial. Mclntosh has developed circuits 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, Mclntosh 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- lntosh 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 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, 14