Sansui QS-1

A 4-channel synthesizer using Sansui's proprietary QS matrix and phase modulation methods for quadraphonic sound reproduction

Overview

The Sansui QS-1 came out when stereo still ruled most living rooms. It promised four-channel sound from any standard two-channel source. Sansui Electric Co., Ltd. built it, and it doesn't amplify or tune. It interprets. Using the proprietary Sansui QS matrix method combined with phase modulation, the QS-1 decodes hidden ambient information in conventional stereo records, tapes, and FM broadcasts. It then redistributes that information across front and rear channels to create a synthesized quadraphonic field. It was part of Sansui's early 1970s push into matrix-based surround, during the short-lived quadraphonic boom. Audio (January 1971, p.17) noted that Sansui engineers had discovered ambient components were already present in stereo signals "in hidden form," and the QS-1 was their solution for sensing and recovering them. It wasn't true discrete 4-channel audio. With the right amplifier and speaker setup, though, it could widen the soundstage beyond the front plane.

The QS-1 measures 395 mm wide, 127 mm high, and 278 mm deep. That's a compact footprint by vintage rack standards, and it holds a dense array of analog circuitry. The front panel has four VU meters for monitoring output balance across the four channels, plus slide-type controls for front-to-rear level distribution. It doesn't produce power itself, but its output levels are substantial: 430 mV at 0 VU in high-output mode and up to 3.5 V maximum, enough to drive downstream power amplifiers without strain.

Key Features

Sansui QS Matrix and Phase Modulation Circuitry

The QS-1 uses two methods together: the Sansui QS matrix method and phase modulation method. Simpler matrix decoders just split and recombine stereo signals. The QS-1 actively manipulates phase relationships to extract spatial cues. Rear channel generation relies on a phase modulation circuit capable of up to 180° shift at 10 kHz, creating time-delayed signals that simulate ambient reflections. Combined with matrix logic, this lets the unit infer directional information not explicitly present in the original stereo mix. A specially developed IC-based quasi-electronic circuit refines the process further, aiming for a less artificial sound field than competitors relying purely on passive resistive networks.

Four-Channel Output with Adjustable Balance

This flexibility accommodates a range of power amplifiers, from modest receivers to high-gain discrete units. Four VU meters are uncommon on processors of this type. They give real-time feedback on channel activity, which helps when fine-tuning speaker balance or diagnosing crosstalk. Front-to-rear balance is set with the slide controls, so listeners can favor front imaging or rear effects.

Multiple Listening Modes with Tailored Frequency Response

The QS-1 offers several listening modes, each with its own frequency shaping. In standard front mode, response is flat from 20 Hz to 20 kHz ±1 dB. The "Rear Solo" mode rolls off highs by -10 dB at 10 kHz, likely to reduce harshness when monitoring ambient content directly. "Concert Hall 1" keeps wide bandwidth with slight variation (+1/-2 dB). "Concert Hall 2" applies dramatic tonal shifts, +6 dB at 50 Hz on the right and +6 dB at 10 kHz on the left, which suggests an attempt to simulate specific acoustic environments through equalization rather than reverb. The "Surround" mode boosts bass at 50 Hz by +6 dB, emphasizing low-frequency ambient energy.

Historical Context

The Sansui QS-1 appeared during the brief quadraphonic era of the early 1970s, when several competing matrix systems vied for dominance. HiFi-Stereo (October 1971, p.66) observed that Sansui's QS system was broadly compatible with Electro-Voice's Stereo-4 and, to a lesser extent, Dynaco's version. Recordings encoded for one could play back with reasonable effect on another. The QS-1 was marketed as a way into four-channel sound without new media, since owners could replay their existing stereo collection in four channels. Studio-Sound (February 1971, p.11) reported that the system had "drawn such rave notices" at the Düsseldorf Hi-Fi Show the previous summer, before retail release. It was positioned not as a standalone component but as a synthesizer to be paired with a stereo amplifier and an additional power stage for the rear channels.

eBay Listings

Sansui QS 1 vintage audio equipment - eBay listing photo 1

SANSUI QS 1 Synthesizer Quadraphonic Decoder Pre Amplifier 4

$993

See all Sansui QS 1 on eBay

As an eBay Partner, we earn from qualifying purchases. This helps support our independent vintage technology research.