Infinity MRA-150 (circa 1985)
Little is documented about the Infinity MRA-150. The record shows it was a mobile (car) amplifier, introduced in the mid-1980s. It appears to have been Infinity's effort at a high-performance amplifier for the then-emerging premium car-audio market. It was designed to take advantage of improved automotive speakers and the arrival of compact disc and high-quality cassette sources in vehicles.
The MRA-150 was advertised with the tagline "A Breakthrough in Amplification," and period ads positioned it as a new breed of mobile amplifier. Audio (May 1985, p.125) listed its power ratings as 75 watts RMS per channel into 4 ohms at less than 1% THD (1 kHz), 60 watts RMS per channel into 4 ohms from 20 Hz to 20 kHz at less than 0.25% THD, and 90 watts RMS per channel into 2 ohms at less than 1% THD (1 kHz). Those are respectable numbers for a mid-1980s car amp, and they suggest a design built for real-world speaker loads.
Circuitry details are thin. A High-Fidelity article (March 1986, p.13) noted that a similar Infinity unit used only moderate amounts of negative feedback and a tightly regulated pulse-width supply - likely a switching power supply - and described the MRA-150 as the more powerful model in that comparison. Limited feedback and a regulated rail were unusual for car amps of the era. That points to an emphasis on clean, stable power delivery rather than big ratings.
No original price, production years, weight, or dimensions have turned up in the surviving documentation. The MRA-150 seems to have been a relatively brief entry in Infinity's catalog. The company is far better remembered for its home and car speakers than for its amplifiers, and the MRA-150 never attracted the cult following of some contemporary car-audio classics.
- Type: Mobile (car) stereo amplifier
- Power output (per Audio, May 1985): 75 W RMS × 2 into 4 Ω (<1% THD, 1 kHz); 60 W RMS × 2 into 4 Ω (20 Hz–20 kHz, <0.25% THD); 90 W RMS × 2 into 2 Ω (<1% THD, 1 kHz)
- Notable design traits: Moderate negative feedback; tightly regulated pulse-width supply (likely switching)
- Period: Circa 1985–1986
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