MCINTOSH MC257 (01) PDF Document

For possible insurance claims or future service, it is important to record the following information for your MCINTOSH MC257:

• Serial Number

• Purchase Date

• Dealer Name

1. For additional connection information, refer to the owner’s manual(s) for any component(s) connected to the MCINTOSH MC257.

2. The MCINTOSH MC257 mutes the speaker output for approximately two seconds when first turned on.

3. For the best performance and safety it is important to always match the impedance of the Loudspeaker to the Power Amplifier connections. The impedance of a Loudspeaker actually varies as the Loudspeaker reproduces different frequencies. As a result, the nominal impedance rating of the Loudspeaker (usually measured at a midrange frequency) might not always agree with the impedance of the Loudspeaker at low frequencies where the greatest amount of power is required. Contact the Loudspeaker Manufacturer for additional information about the actual impedance of the Loudspeaker before connecting it to the MCINTOSH MC257.

4. In the event the MCINTOSH MC257 overheats, due to improper ventilation and/or high ambient temperature, the protection circuits will activate. The Front Panel Power Guard LED will continuously indicate ON and the audio will be muted. When the MCINTOSH MC257 has returned to a safe operating temperature, normal operation will resume.

5. When discarding the unit, comply with local rules or regulations. Batteries should never be thrown away or incinerated but disposed of in accordance with the local regulations concerning battery disposal.

The pin configuration for the XLR Balanced Input/Output Connectors on the MCINTOSH MC257 is as follows:

• PIN 1: Shield/Ground

• PIN 2: + Input/Output

• PIN 3: – Input/Output

The MCINTOSH MC257 Power Control Input receives an On/Off signal from +5 to +12 volts. The Power Control Output will in turn provide a +12 volt Output Signal with a total current up to 50mA. An additional connection is for controlling the illumination of the MCINTOSH MC257 Power Output Meters. The 1/8 inch stereo mini phone plug connects to a McIntosh Preamplifier or A/V Control Center Power Control Output.

When using cables with spade lugs for Loudspeaker Connection on the MCINTOSH MC257, the spade lugs need an opening of at least 3/10 inch (7.6mm).

The MCINTOSH MC257 can be placed upright on a table or shelf, standing on its four feet. It can also be custom installed in a piece of furniture or cabinet. If custom installed, the four feet may be removed from the bottom of the unit. The four feet together with the mounting screws should be retained for possible future use.

Always provide adequate ventilation for your MCINTOSH MC257. Cool operation ensures the longest possible operating life. Do not install the MCINTOSH MC257 directly above a heat generating component such as a high powered amplifier. If all components are installed in a single cabinet, a quiet running ventilation fan can be a definite asset.

A custom cabinet installation should provide the following minimum spacing dimensions for cool operation:

• Allow at least 6 inches (15.24cm) above the top.

• Allow 2 inches (5.08cm) below the bottom.

• Allow 3 inches (7.62cm) behind the rear panel.

• Allow 2 inches (5.08cm) on each side of the Power Amplifier.

Ensure that airflow is not obstructed. Allow 7/8 inch (2.22cm) in front of the mounting panel for clearance. Be sure to cut out a ventilation hole in the mounting shelf according to the dimensions in the installation drawings.

Caution: Do not connect the AC Power Cord to the MCINTOSH MC257 Rear Panel until after the Loudspeaker Connections are made. Failure to observe this could result in Electric Shock.

To connect loudspeaker hookup cables, please follow these steps:

1. Rotate the top of the Output Terminal Post counterclockwise until an opening appears.

2. Insert the Loudspeaker hookup cable into the Output Terminal Post opening or the cable spade lug around the center post of the Output Terminal.

3. Rotate the top of the Output Terminal Post clockwise until it is finger tight.

4. Place the supplied McIntosh Wrench over the top of the Output Terminal and rotate it one quarter of a turn (90°) to secure the Loudspeaker Cable Connection. Do not over tighten.

To prepare bare wire cable ends for attachment to the MCINTOSH MC257 Power Amplifier:

Carefully remove sufficient insulation (approximately 0.5 inches or 12.7mm) from the cable ends. If the cable is stranded, carefully twist the strands together as tightly as possible.

Notes:

1. If desired, the twisted ends can be tinned with solder to keep the strands together.

2. The prepared bare wire cable ends may be inserted into spade lug connectors.

3. Banana plugs are for use in the United States and Canada only.

When connecting Loudspeakers to the MCINTOSH MC257 it is very important to use cables of adequate size to minimize power loss. The size is specified in Gauge Numbers or AWG (American Wire Gauge). The smaller the Gauge number, the larger the wire size.

1. Attach the previously prepared bare wire cable ends into the banana plugs and secure the connections.

2. Rotate the top of the Output Terminal Post clockwise until it is finger tight.

3. Connect the Loudspeaker hookup cables with banana plugs into the hole at the top of the terminal to the COM (Negative) Output Terminal and the (+) Positive Output Terminal identified as 4Ω (ohms) or 8Ω (ohms) connection to match the impedance of the Loudspeaker, being careful to observe the correct polarities.

4. Place the LOAD Switch on the rear panel of the MCINTOSH MC257 to either the 4 or 8 Ohm Setting, to match the impedance of the majority of the loudspeakers connected.

WARNING: Loudspeaker terminals are hazardous live and present a risk of electric shock. For additional instruction on making Loudspeaker Connections contact your McIntosh Dealer or McIntosh Technical Support.

Connect the Loudspeaker hookup cables to the MCINTOSH MC257 COM (Negative) Output Terminal and Positive Output Terminal identified as 4Ω (ohms) or 8Ω (ohms) connection to match the impedance of the Loudspeaker, being careful to observe the correct polarities. Insert the spade lug connector or prepared section of the cable end into the terminal side access hole, and tighten the terminal cap until the cable is firmly clamped into the terminals so the lugs or wire cannot slip out.

WARNING: Loudspeaker terminals are hazardous live and present a risk of electric shock. For additional instruction on making Loudspeaker Connections contact your McIntosh Dealer or McIntosh Technical Support.

If the Loudspeaker’s impedance is in-between the available connections (4 and 8 ohms), use the nearest lower impedance connection. For example, if your speaker is rated at 6 ohms, you should use the 4 ohm connection terminal on the MCINTOSH MC257 and set the rear panel LOAD switch to 4 Ohms.

• Meter (Left, Center, Right): Indicates the power output of the Front Left, Front Center, and Front Right channels of the amplifier.

• POWER GUARD LEDs: These LEDs indicate when the POWER GUARD circuitry has been activated for specific amplifier channels (LF1, LB2, RB3, C4, RF7, LS5, RS6).

• METER LIGHTS Switch: Turns the illumination of the Left, Center, and Right Channel Meter Displays On or Off.

• Standby Power On Indicator: A red LED that illuminates when the amplifier is in standby mode.

• POWER Switch: A 3-position rotary switch that turns AC Power Off, sets to Remote control, or turns AC Power On.

There are two ways to have AC Power switched ON to the MCINTOSH MC257:

REMOTE Setting: When the MCINTOSH MC257 Power Control Connection (ZA and/or ZB) receives a Power Control Signal from a Preamplifier or A/V Control Center, it will turn On automatically when the MCINTOSH MC257 POWER Control switch is set to the REMOTE Setting.

ON Setting: When the MCINTOSH MC257 POWER Control switch is set to the ON position, it will become active (Zone A only). To switch the MCINTOSH MC257 OFF, place the POWER Control in the OFF position.

The MCINTOSH MC257 has several channel operation modes.

Zone A Operation: This occurs when the POWER Control is positioned to ON or set to REMOTE and receiving a Power Control Signal in the ZA connector.

Zone A/B Operation: This occurs when the POWER Control is in the REMOTE position and both the ZA and ZB connectors are receiving Power Control Signals.

Rotate the METER LIGHTS Switch to the ON position to Illuminate the three Front Panel Meters for the Left, Center and Right Channels. When Lights are Off, the meter lights are turned off, but the Meters will continue to indicate the power output.

Note: When the Power Control Input of the MCINTOSH MC257 is connected to an Audio Preamplifier or A/V Control Center with Remote Meter Illumination Control, the Meter Illumination will automatically be remotely controlled (On/Off).

The meters respond to all the musical information being produced by the amplifier. They indicate to an accuracy of at least 95% of the power output with only a single cycle of a 2000Hz tone burst.

The MCINTOSH MC257 incorporates Power Save Circuitry to automatically place the unit into the power-saving Standby Mode approximately 30 minutes after there has been an absence of an audio input signal.

• When a Power Control Connection exists between the MCINTOSH MC257 and a Preamplifier or A/V Control Center with Power Save Circuitry, the AUTO OFF Switch in the ENable (EN) position is bypassed.

• In the event there is no Power Control Connection and the Power Save Circuitry is activating inappropriately, you can place the AUTO OFF Switch on the rear panel in the DISable (DIS) position.

Note: If the Power Save Circuitry has switched Power to the MCINTOSH MC257 OFF, place the POWER switch in the OFF Position and then in the ON position to reset the circuitry.

Place the Load Impedance Switch, located on the rear panel, to the 4 Ohms position if the Loudspeakers connected to the MCINTOSH MC257 are not 8 Ohms but 4 Ohms. If your loudspeakers are 8 Ohms, set the switch to the 8 Ohms position.

The patented McIntosh Power Guard circuit on the MCINTOSH MC257 prevents the amplifier from being overdriven into clipping. An overdriven amplifier can produce audible and inaudible distortion levels exceeding 40%, which can damage loudspeaker tweeters.

Power Guard works as a waveform comparator, monitoring both the input and output waveforms. If the amplifier is overdriven, the difference between the two signal waveforms will exceed 0.3%. When this happens, Power Guard activates the PG light and a dynamic electronic attenuator at the amplifier input reduces the input volume just enough to prevent any further increase in distortion. This process is so fast that there are no audible side effects, preserving the sonic purity of the music reproduction.

In the event it is necessary to repack the equipment for shipment, the equipment must be packed exactly as shown in the packing diagram. It is very important that the four plastic feet are attached to the bottom of the equipment. Four 1/4 – 20 x 2-1/2 inch screws and washers must be used to fasten the unit securely to the bottom pad and shipping skid. This will ensure the proper equipment location on the bottom pad. Failure to do this will result in shipping damage.

Use the original shipping carton and interior parts only if they are all in good serviceable condition. If a shipping carton or any of the interior part(s) are needed, please call or write the Customer Service Department of McIntosh Laboratory.

The correct part numbers are as follows: