McIntosh MC 2255 Brochure
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Page 1
McINTOSH QUALITY BEGINS WITH CAREFUL DESIGN FOR COOL OPERATION To achieve long trouble-free life in an amplifier it is essential to have cool operation. As little as one de- gree (centigrade) rise in temperature can reduce the operating life of the amplifier 10%. Mclntosh has extended the life of its amplifiers by engineer- ing for cool operation. Long life of a Mclntosh is not just a claim. More than 80% of the Mclntosh ampli- fiers produced since 1949 are still in service today. Mclntosh cool operation requires a combination of careful design of the output circuit, containing the output circuit in a mechanical housing that per- mits the use of generous sized heat sinks to provide great heat dissipation capability along with chassis construction that permits adequate ventilation, then correctly matching the cool operating output circuit to the loudspeakers with a Mclntosh de- signed and manufactured auto-transformer. The Mclntosh output circuit uses bipolar epitaxial output transistors in a cleverly inventive design that keeps the circuit components cool, extending the long trouble-free life of the components. The circuit has the ability to recognize the power de- mands of the program material and then to acti- vate only as much of the output circuit as is needed to satisfy that demand. AH this occurs without the crossover distortion found in conventional solid state output circuits. (The amplifier circuit is a pa- tented Mclntosh design U.S. patent #3526847.) The Mclntosh output stages are mounted on heat sinks that have maximum surface area of cooling capability, the largest for equivalent power in the industry. The super sized heat sinks are placed in an air tunnel chassis design that occupies the en- tire space from the bottom of the amplifier to the top. Cooling air, flowing through the air tunnel, easily dissipates any life limiting heat generated.
Page 2
VERSATILE MclNTOSH POWER AMPLIFIERS DELIVER FULL POWER- ALWAYS The superior Mclntosh output circuit demands a superior method of coupling the amplifier output to the loudspeaker load. The Mclntosh designed and manufactured autotransformer is a silent giant that insures better performance and protection and superior interaction between amplifier and speaker. Its use provides many unseen benefits. The autotransformer interconnection insures com- plete stability of the amplifier. Other amplifier cir- cuits need additional component considerations to prevent instability with its subsequent threat to the life and performance of the amplifier. It is the ideal method of matching the output circuit to the loud- speakers. Transistors, used in amplifier output cir- cuits, are designed to work into an optimum low impedance load. Frequently amplifier performance will be compromised by speaker impedance varia- tions with frequency or by the use of multiple speakers which modify the impedance as seen by the output of the amplifier. Without the Mclntosh autotransformer, variables, such as these, can cause restricted performance, output transistor heating and then circuit failure. A second benefit of the Mclntosh autotransformer is the protection provided in the event of a failure in the output circuit. Should any direct current com- ponent appear at the output, the autotransformer will conduct the speaker damaging DC directly to ground. Your expensive loudspeakers are protec- ted from this potentially damaging circumstance. Here's a third benefit of the Mclntosh autotrans- former. It not only provides the output transistors an ideal load and is the path that conducts any DC away from the loudspeaker, it also contributes a flexibility in loudspeaker connecting capability not otherwise possible. For safe operation ordinary am- plifier output circuits are usually restricted to oper- ate into 4 or 8 ohms. In stereo, the Mclntosh auto- transformer perfectly matches the output circuit to 1, 2, 4 or 8 ohms. In mono, (Mclntosh stereo ampli- fiers can be interconnected for mono and deliver twice the power) the autotransformers provide matching ½,1, 2, 4, 8 or 16 ohms. In addition, in either stereo or mono, the autotransformer pro- vides a 25 volt output that may be used to feed multiple loudspeakers for background music and the like. Truly, the Mclntosh autotransformer is an engineering marvel that enhances amplifier per- formance without any technical or performance drawbacks. THE MclNTOSH (EXCLUSIVE) POWER GUARD MUSIC PROTECTION CIRCUIT Improved recordings and recording techniques have imposed higher power demands on today's amplifiers. Poorly designed amplifiers, of which there are many, can present music listeners with a form of harsh unpleasant distortion due to ampli- fier overload (hard clipping). Clipping, which looks and acts like non musical square waves, is caused when the amplifier is asked to produce more power output with low distortion than it is capable of or designed to deliver. Amplifiers, when driven to clip- ping, can deliver up to 4O% harmonic distortion. Distortion decreases the pleasure and enjoyment of listening. This form of distortion (clipped signal) also produces extra heat energy which will damage most speakers. Mclntosh leadership in engineering has developed the Power Guard circuit which - (1) dynamically prevents power amplifiers from be- ing overdriven into hard clipping-(2) assures that the amplifier will produce its maximum output without increased distortion -(3) protects your speaker from excessive heating. Power Guard is a patented Mclntosh design (U.S. patent #4048573).