McIntosh MPI 4 Maximum Performance Indicator (1975)
MPI-4 Description Introduced in 1973, McIntosh MPI-4 Maximum Performance Indicator was until 1977. It was a fairly expensive piece. Relatively few MPI-4 units are around today. The McIntosh MPI-4 is an elaborate, yet compact, laboratory grade instrument that allows you to maximize the performance of your complete audio system and individual components. It continuously monitors the quality of the performance of a stereo system. It can sample and display signals from the tuner, preamplifier and power amplifier without reconnecting cables. As a tuning aid exact FM station selection and precise tuning is seen. Displays of FM are signal strength, modulation percentage and multipath interference; of audio signals are stereo balance, amplitude, phase and channel separation. Output power of the power amplifier can be seen at any instant during program performance, or stored to develop a trend over several minutes. With the addition of test records, the MPI-4 can show compliance and tracking ability of phono pickups, preamplifier and power amplifier frequency response, audio distortion and stereo speaker balance. Dual trace mode provides direct comparison between Left and Right stereo channels. Even today, the MPI-4 is a tool that provides valuable info for improving a stereo system.
Features and functions include:
Dual Trace Each channel of stereo signal is displayed individually in the dual trace mode of operation. Signal comparison assists in comparison of recordings, quality of stereo source information and more.
Level Stereo signal level is displayed as two vertical columns on the screen. Column height is determined by power or amplitude of the input signal. Peak-Hold function allows close comparison between the right and left channel peak levels.
Phono Cartridge Calibration The MPI-4 aids in protecting your record investment, extend the life of your records, and reduce needle wear when the turntable is properly set up. Using the MPI-4 with test recordings will assist in this proper set up. The display assists in properly adjusting for proper tracking force, best tracing vs tracking force, anti-skate, proper phasing, and channel separation.
FM Tuning FM tests include signal strength, center-channel FM tuning and a reference for multipath distortion elimination. The image is a display of the tuner IF curve. Signal strength is the vertical axis. Horizontal center is the center of the detector and IF curves. Proper tuning yields minimum distortion and maximum listening pleasure in FM broadcasts.
Phase Program material that is 'out of phase' sounds unnatural and thin; 'in phase' sounds alive and rich. Occasionally a program source will be 'out of phase.' On the MPI-4 you can see the phase relationship so you can correct the condition.
Balance Accurate system balance assures you of full stereo pleasure, The MPI-4 gives you a visual indication of the balance of your stereo system. You can check and correct the output balance of your stereo phono cartridge, tape recorder, tuner, or any part of your stereo system. You will know when your stereo system is in balance when you use an MPI-4.
Channel Separation The MPI 4 shows the stereo separation from all stereo program material. The display changes position and shape with the program material to permit interpretation of what the display means to your listening enjoyment. You see what makes a good stereo record sound good. You will know why your records sound the way they do.
Multi-Path display Multipath reception deprives you of FM listening enjoyment in several ways: * noise level increase * distortion is introduced into the program material * stereo separation is reduced * the stereo effect may be completely lost * stereo indicators may fail to function
Condition This unit has received a SuperGrade Level IV restoration by a trained audio tech with over 40-years experience. The restoration includes a new CRT display. The high-voltage section has new film capacitors with improved specs for super-long life and reliability. All electrolytic caps have been replaced with long-life, high-performance parts. All lamps have been replaced. Overall better than factory-new as over 66 improved components were installed.