The Unitra M-531S, also known as the Tesla ANP 493 in Czechoslovakia, is a stereo cassette recorder produced by Poland's Unitra ZRK between 1975 and 1979. This device exemplifies the robust engineering and design characteristic of Eastern European audio equipment from that era. The M-531S features a compact, desktop-friendly design with dimensions of 300 x 75 x 225 mm and a weight of approximately 3.5 kg. Its casing is primarily plastic, accented with aluminum panels on the top and front, giving it a sleek yet sturdy appearance. The device includes a built-in power supply and an integrated amplifier, delivering 2 x 6 watts of output power. It offers separate volume controls for each channel and a combined recording level control, with a needle indicator to monitor recording levels. Connectivity options include DIN connectors for microphones, turntables, tape recorders, tuners, and speaker connections supporting both 4 and 8-ohm impedances. Operating at a tape speed of 4.76 cm/s, the M-531S covers a frequency range of 50-12,000 Hz, providing respectable audio quality for its time. While the recording quality is standard, the built-in discrete amplifier is noteworthy, delivering impressive sound output with minimal noise—a feature distinguishing it from many contemporaneous devices. The M-531S is praised for its user-friendly interface, featuring straightforward mechanics, including a pause function and non-locking fast rewind buttons. The device's ability to connect to external speakers with selectable impedance adds to its versatility, catering to various user preferences. This model was distributed as kits from Poland and assembled in Czechoslovakia, likely at Tesla's facilities in Pardubice. Variations of the M-531S exist, with differences in features such as counters, recording level indicators, and panel finishes, reflecting the collaborative manufacturing practices of the era. This interesting and rare tape recorder was donated to the Retro Audio Museum by one of our followers, Pavel Kadraba, a private collector from Slovakia. We are very grateful to him for this donation and hope to see him at our museum one day!
