dbx Model 158
Eight channels of simultaneous encode and decode, a spare module in the frame, and a price that made small studios do the math.
Overview
The Model 158 is the most comprehensive of dbx's 150 series noise reduction units. It was pitched at the small multi-track studio that wanted professional-grade dbx encoding without buying into the professional line. In practice that meant eight channels of simultaneous encode and decode, so the operator never has to flip a unit between record and playback modes, and neither does the machine. For a project studio running a half-inch eight-track, that convenience was the whole point.
dbx advertised more than 30 dB of noise reduction, and that was the number that counted for anyone doing multiple overdubs. Every bounce on a narrow-format machine stacks tape hiss on top of tape hiss. 30 dB of reduction let a small studio keep bouncing tracks without an audible build-up of noise. Recording-Engineer (June 1977, p.66) described the Model 158 as offering the semi-professional recordist or small studio the advantages of dbx's professional systems, including 30 dB of noise reduction plus 10 dB of additional recorder headroom. It called the circuit a classic 2:1 mirror-image compander that compresses the signal's dynamic range going to tape and fully reconstructs the original input on playback.
Here is what separated dbx from its competitors. dbx's patented circuitry does not require critical matching of encode and decode levels, so no reference tones and no metering are necessary. Anyone who has set up a compander that demands precise level calibration will know how much friction that removes from a session. The 158 was also built to be fully compatible with dbx's professional studio noise reduction equipment. A recording made on a 158 can be decoded by any studio running professional dbx gear, and the reverse holds true as well. That meant a small studio could hand a tape to a larger facility without re-tracking.
The frame is modular, and dbx included a spare one-channel noise reduction module inside it. A dead channel in the middle of a session stops the session, and the spare module plus the modular construction was there to keep downtime to a minimum. Interface is through both Molex multi-pin and phono connectors, which allowed rapid patching into a variety of machines rather than locking the owner into one wiring scheme. The system carries its own power supply module. Studio Sound (March 1978, p.29) covered the launch as budget dbx noise reduction for the small multi-track studio, noting the semi-professional positioning against the established professional series and the 30 dB-plus noise reduction figure.
Pricing moved around during the Model 158's run. Early UK coverage listed it at £1614, with a later advertisement quoting £1559 and an approximate US figure of $2400. By the 1979 listings the UK list price had settled at £1,498.00. Studio Sound (May 1979, p.27) carried the £1,498.00 figure alongside the pitch that the 158 was ideal for use with Teac, Otari, Itam and Dokorder machines - the four-track and eight-track recorder brands that defined the small-studio market the unit was built for. The same advertising positioned the four-channel Model 155 alongside it at £325.00, and earlier Studio Sound coverage (October 1978, p.39) had listed the 155 at £364, so the whole 150 series saw price movement across the period.
The Model 158 is a semi-professional version of dbx's professional series, not a professional unit with a budget badge. dbx said so plainly in its own advertising. The buyer got the same compatibility, the same level-matching-free circuitry, and the same 30 dB-plus reduction claim in a modular eight-channel frame with a spare module, at a price a small studio could justify. The sales copy leaned on four claims: unbeatable 30 dB noise reduction, total compatibility with dbx professional equipment, modular format, and simplicity of operation. Those are marketing claims. The compatibility and modularity points, though, are structural facts about how the unit is built.
The Model 158 is an eight-channel simultaneous encode/decode unit from the 150 series. That makes it more capable than the two- and four-channel budget units in the same family, and more convenient than a switchable unit that forces mode changes between record and playback. The spare module inside the frame helps when one channel goes down and there's no donor unit on the shelf. The Molex and phono connectivity means it can be integrated into a variety of setups rather than being tied to one recorder. Documentation is thin compared to dbx's compressor line, and the period coverage that survives is largely advertising and launch announcements rather than deep bench reviews. Buyers should expect to verify condition and module completeness carefully, since there is little published test data to lean on.
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