McIntosh MX115 Tuner-Preamplifier (1968)

Name: McIntosh MX115
Brand: McIntosh

The McIntosh MX115 is a classic tuner-preamplifier that marked a pivotal moment in McIntosh Laboratory’s transition from vacuum tube to solid-state technology. Introduced in 1968, the MX115 combined a high-fidelity preamplifier with a sensitive FM/AM tuner in a single chassis, offering audiophiles a versatile and reliable control center for their audio systems. Though it lacks built-in power amplification, its robust preamp design and exceptional tuner performance made it a favorite among discerning listeners during its production run, which lasted until 1977.

With its iconic blue illumination, precision meters, and the legendary McIntosh build quality, the MX115 remains a sought-after component for vintage audio enthusiasts and collectors.

Key Features

Solid-state design with no tubes
McIntosh Unity Coupled Circuitry for low distortion
Integrated FM/AM tuner with signal strength meter
Separate bass and treble tone controls with loudness contour
Mode and filter switches for enhanced FM reception
Phono inputs for both MM (moving magnet) and MC (moving coil) cartridges
Front-panel 1/4" headphone jack
Illuminated tuning and signal strength meters
High-quality rotary controls and switches

Specifications

Parameter	Specification
Year of Production	1968–1977
Category	Tuner-Preamplifier (Receiver)
Design	Solid-state
Power Output	Preamplifier only (no power amplification)
Tuner Bands	FM, AM
FM Sensitivity	1.7 μV for 30 dB quieting
Phono Input Sensitivity	MM: 2.5 mV for 0.5V output MC: 0.25 mV for 0.5V output
Input Impedance	High-level: 47k ohms MC Phono: 100 ohms
Output Impedance	Fixed: 600 ohms Variable: 47k ohms
Total Harmonic Distortion	<0.1% (typical)
Frequency Response	20 Hz – 20 kHz (±0.5 dB)
Headphone Output	1/4" jack, front panel
Power Requirements	120V AC, 60 Hz
Dimensions (W×H×D)	19" × 6.5" × 15.5"
Weight	28 lbs (12.7 kg)

Historical Context

The McIntosh MX115 represents a significant chapter in the evolution of high-end audio. As one of McIntosh’s earliest solid-state tuner-preamps, it symbolized the company’s successful shift from tube-based electronics to modern transistorized circuitry—without compromising the sonic integrity and engineering excellence the brand was known for.

During the late 1960s and 1970s, FM broadcasting was gaining popularity for its superior sound quality, and the MX115 delivered exceptional tuner performance with high sensitivity and selectivity. Its inclusion of both MM and MC phono inputs catered to serious vinyl enthusiasts, while the Unity Coupled Circuit design ensured minimal distortion and wide bandwidth.

The MX115 was often paired with McIntosh power amplifiers like the MC240 or MC3500, forming the backbone of high-performance audio systems in homes and studios alike. Its durability and modularity contributed to long-term reliability, reinforcing McIntosh’s reputation for building equipment that lasts.

Sound Signature

The MX115 delivers a warm, smooth, and highly detailed sound that remains engaging by modern standards. The preamplifier section is known for its low noise floor and excellent channel separation, preserving the dynamics and spatial cues of the original recording.

The phono stage—especially for a solid-state design of its era—is widely praised for its musicality and ability to extract nuance from vinyl. The MC input, in particular, is sensitive and well-matched to low-output moving coil cartridges. The FM tuner offers crisp, clear reception with strong stereo imaging and minimal interference, thanks to precise filtering and robust front-end design.

Maintenance and Restoration Tips

While the MX115 is known for its durability, units over 40 years old often require servicing to perform at their best. Here are common issues and recommended maintenance steps:

Capacitor Replacement: Electrolytic capacitors in the power supply and audio path degrade over time. A full recapping is strongly recommended to prevent noise, hum, or component failure.
Cleaning Controls: Rotary switches and potentiometers can become noisy due to oxidation. Use contact cleaner designed for audio equipment (e.g., DeoxIT) and exercise the controls repeatedly after application.
Tuner Alignment: If FM reception is weak or unstable, a professional alignment of the tuner section may be necessary.
Meter Lamps: The illuminated tuning and signal strength meters use small incandescent bulbs that may burn out. Replacement bulbs are available from specialty audio restoration suppliers.
Bias and Calibration: Ensure transistor bias points are checked and calibrated during servicing to maintain optimal performance.
Originality Preservation: For collectors, retaining original components and finishes increases value. Use NOS (New Old Stock) or period-correct replacements when possible.

Collectibility and Market Value

The McIntosh MX115 holds a collectibility rating of 7/10. It appeals to vintage audio collectors, especially those focused on the transition era of solid-state development and the early years of high-fidelity FM reception.

Market Value: $300 – $600 USD
Factors Affecting Value:
Original condition (chrome, faceplate, knobs)
Operational status
Service history
Presence of both MC and MM phono functionality
Working meters and illumination

Fully serviced units with clean cosmetics command higher prices, particularly when sold with original documentation or packaging.

Conclusion

The McIntosh MX115 stands as a milestone in audio engineering—a bridge between the tube era and the solid-state future. Its combination of superb preamplification, excellent tuner performance, and legendary McIntosh build quality ensures its enduring appeal. Whether used as a centerpiece in a vintage system or preserved as a collector’s item, the MX115 remains a testament to McIntosh’s commitment to high-fidelity excellence.