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Instructions for safely unpacking the MC3500, including tube protection and safety precautions.
Procedure for attaching speaker cables to the amplifier's output terminals.
Important warnings regarding hazardous live terminals and risk of electric shock.
Explanation of Sentry Monitor function and how to reset it.
Detailed electrical and performance specifications of the MC3500 amplifier.
The McIntosh MC3500 is a high-fidelity mono tube power amplifier designed to deliver exceptional musical reproduction. It embodies traditional McIntosh standards of excellence, offering a powerful and sonically transparent audio experience. The amplifier is engineered to drive high-quality loudspeaker systems with its substantial power output and advanced circuitry, ensuring accurate and detailed sound.
The MC3500 serves as a mono tube power amplifier, meaning each unit is dedicated to amplifying a single audio channel. This design choice allows for optimal channel separation and power delivery, contributing to a more immersive and dynamic soundstage. It is capable of delivering 350 watts of power into 2-, 4-, or 8-ohm loudspeakers, making it versatile enough to pair with a wide range of speaker systems. The amplifier's reproduction is described as sonically transparent and absolutely accurate, aiming to deliver "The Sound of the Music Itself."
At its core, the MC3500 utilizes McIntosh's patented Unity Coupled Circuitry, a design known for providing low distortion, extended frequency response, and cool operating output tubes. This circuitry is complemented by a Multifilar Wound Output Transformer, which is integral to the Unity Coupled design. This transformer features three trifilar wound primaries (for cathodes, plates, and screens) and a secondary winding wound together with the primaries. This construction ensures very close primary to secondary coupling, resulting in a flat frequency response and wide power bandwidth.
The amplifier supports both balanced and unbalanced input connections. Balanced connections are particularly beneficial as they help guard against induced noise, allowing for longer cable runs without compromising sound quality. This flexibility ensures compatibility with various preamplifiers and audio sources.
A key protective feature is the Sentry Monitor Tube Protection. This system continuously monitors the amplifier's output and activates in the event of a large impedance mismatch, a short circuit at the output terminals, or a tube failure. When activated, Sentry Monitor prevents potentially destructive levels of current from flowing, safeguarding the amplifier and connected equipment.
Another innovative protection system is the Power Guard Screen Grid Sensor (SGS). This feature helps prevent premature vacuum tube failure by monitoring the screen grid current in the EL509S output vacuum tubes. If the current becomes too high, the Power Guard SGS circuit dynamically attenuates the input signal in real time to keep the vacuum tubes operating at safe levels. An amber LED will flash to indicate when Power Guard SGS is engaged.
The MC3500 also incorporates a special power supply featuring a very large core power transformer and large filter capacitors. This robust power supply design ensures stable operation and consistent power delivery, crucial for maintaining audio quality under varying demands.
Operating the MC3500 involves several user-friendly controls and indicators. The front panel features a prominent Power Output Meter, which displays the power output level in Watts and Decibels. This meter provides visual feedback on the amplifier's performance. A Meter Control Knob allows users to select between different meter functions: "WATTS" for continuous real-time display of current output, and "HOLD" to display the highest peak output until a greater peak is registered. In "HOLD" mode, if no greater peak is read, the meter needle will gradually lower at a rate of approximately 6dB per minute. The meter light can also be controlled, either permanently off or powered on/off by a connected preamplifier or A/V control center via a Power Control Cable.
The amplifier includes a Power Knob on the front panel, which allows for manual On/Off control. Alternatively, setting the knob to "REMOTE" enables automatic power control by a connected preamplifier, turning the MC3500 on or off in sync with the preamplifier. An LED indicator on the front panel illuminates when the MC3500 is connected to an active AC outlet.
Upon initial power-on, the MC3500 enters a "Warmup" period, indicated by the illuminated WARMUP LED. During this time, no sound is produced, and the Power Output Meter needle gradually rises to show the warmup percentage. Once the needle reaches 100%, the amplifier begins playing sound, the WARMUP LED switches off, and the meter returns to displaying the appropriate output.
The rear panel hosts several important connections and switches. Input options include Balanced XLR connectors and Unbalanced RCA connectors. An Input Mode Switch allows users to toggle between Balanced and Unbalanced inputs, ensuring compatibility with various audio sources. Output terminals for loudspeakers are robust, gold-plated binding posts designed for trouble-free connections.
For system integration, the MC3500 includes Power Control In and Out jacks. The Power Control In jack receives an On/Off signal from a connected McIntosh component, while the Power Control Out jack sends an On/Off signal to other connected McIntosh components. These 3.5mm mini-phone plug connections facilitate synchronized power management within a McIntosh system. Additionally, an illumination control connection is available for controlling the Power Meter's illumination when connected to a compatible McIntosh preamplifier.
The MC3500 also features an "Auto Off" function, which is part of its power-saving circuitry. This function automatically places the amplifier into a standby mode approximately 30 minutes after an absence of an audio input signal. An "Auto Off" switch on the rear panel allows users to enable or disable this function. If a Power Control Connection exists with a preamplifier that has power save circuitry, the MC3500's "Auto Off" switch is bypassed.
The MC3500 is designed for long-term reliability and performance, with several features contributing to its durability and ease of maintenance. The vacuum tube sockets for small signal tubes are constructed with ceramic bases and gold-plated contacts, which provide protection from atmospheric contamination and ensure stable connections over time. The output tube sockets include "Air-Pipe" cooling at their bases, contributing to the long-term operation and lifespan of the tubes.
Adequate ventilation is crucial for extending the trouble-free life of the MC3500. The design allows air to flow through ventilation holes on the bottom of the amplifier, with warm air escaping from the top. Specific clearance recommendations are provided to ensure unobstructed airflow around the unit.
In the event of a Sentry Monitor activation, the MC3500 will power off, and the Standby LED will flash. To reset the Sentry Monitor Protection Circuitry, the user needs to turn the Power Control Knob to OFF and then back to ON. If the Sentry Monitor continues to engage, it indicates a persistent problem that requires investigation, such as checking for shorted loudspeaker wires or a defective tube.
The MC3500 is designed with no user-serviceable parts, including the vacuum tubes. Any repairs, including tube replacement, must be performed by an authorized McIntosh Service Agency. This ensures that the amplifier is serviced by trained professionals using genuine parts, maintaining its performance and safety standards.
For shipping, special instructions are provided to protect the vacuum tubes. A foam insert, which is removed during initial unpacking, must be re-inserted to secure the tubes during transport. The manual emphasizes the importance of using the original shipping carton and interior packing materials, which are designed to protect the equipment. If these materials are needed, customers are advised to contact McIntosh Customer Service.
The gold-plated input jacks and output binding posts are designed to provide trouble-free connections, resisting corrosion and ensuring optimal signal transfer over time. This attention to detail in component quality contributes to the overall reliability and low maintenance requirements of the MC3500.
General| Input Sensitivity | 0.5V |
|---|---|
| Signal to Noise Ratio | 105dB |
| Input Impedance | 100k ohms |
| Power Output | 350 Watts |
| Frequency Response | 20Hz to 20kHz |
| Total Harmonic Distortion | 0.5% |
| Dimensions | Width 17-1/2 inches (44.5 cm) Height 10-1/2 inches (26.7 cm) Depth 20 inches (50.8 cm) including connectors |
| Output Impedance | 4, 8, 16 ohms |
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