Marantz ST320L

A PLL MPX tuner that sells for the price of a decent dinner - and sometimes for nothing at all.

Overview

The Marantz ST320L is a stereo tuner, and every source agrees on that much. Depending on the listing, it's a "Hi-Fi Tuner," an "FM/AM Tuner," a "Stereo Tuner," or a "Radio Tuner." Nobody disputes the brand or the model number. The name gets typed every way you can think of: ST320L, ST 320L, ST-320L, St320L. Collectors searching auction sites should try all of them, because listings scatter across the variants and a bargain can hide behind a missing hyphen.

The available documentation records no production year, no original retail price, and no dimensions or weight. The ST320L has never gotten the archival attention that Marantz's big receivers and tube-era components get. What survives is a paper trail of owner listings, service documentation, and one notable spec - a 66dB FM signal-to-noise ratio, reported by Audio Trader. That figure is respectable for a tuner of this class and suggests the front end was taken seriously.

The tuning section is built around PLL MPX - phase-locked loop with a multiplex decoder - and at least one manual aggregator files the unit under "digital tuner." Owners describe a weighted tuning dial that "works as smooth as butter." A tuner lives or dies on how it feels to sweep across the band, and a properly weighted dial with intact bulbs is a large part of why anyone bothers with a separate tuner in an age of streaming.

Key Features

PLL MPX Tuning with a Weighted Dial

The PLL MPX designation points to a phase-locked loop tuning system feeding a multiplex stereo decoder - the standard architecture for solid-state FM tuners of the era. What owners talk about, though, is the dial. One eBay seller describes the weighted tuning dial as working "as smooth as butter," and notes that the bulbs are all working perfectly. On a tuner this old, working dial lamps matter. They are frequently the first thing to fail, and replacing them can be fiddly. A unit with intact illumination and a smooth tuning mechanism has either been cared for or barely used.

AM/FM Bands — With a Caveat

Here the sources split. eBay US, eBay UK, and HifiShark all describe the ST320L as an AM/FM tuner. eBay Australia and eBay.ie listings claim LW/MW/FM coverage instead, and a Gumtree listing calls it an "AM/FM hifi tuner." Buyers in North America should not assume longwave reception without confirming the specific unit. Buyers in Europe should check which band set their example actually carries.

Service Documentation and Circuit Access

A service manual for the ST320/ST320L exists and circulates through manual repositories. It contains a full circuit diagram.

For a technician, that documentation is the difference between a repairable tuner and a doorstop. The schematic is out there, so the ST320L is not a black box.

Collectibility & Value

The ST320L does not command collector premiums. Recent market evidence is scattered and modest: a Gumtree listing in Locks Heath, Hampshire at £20, an auction bid of €65 recorded by HifiShark in July 2025, and a free-collection listing in Duddingston, Edinburgh. One eBay seller calls it a "highly sought after Marantz tuner," but the actual prices tell a more sober story.

Condition varies widely. Audio Trader graded one example as "Excellent" and noted it passed a seven-point functional test, with two items marked not applicable to the unit. A UK eBay listing was more candid: "quite an old unit with some scratches." No common failure modes, repair procedures, or spare-parts availability information turned up in the research, so buyers should inspect dial lamps, tuning smoothness, and band coverage in person where possible.

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