The dbx 155 was a professional four-channel noise reduction unit introduced by dbx during the mid-1970s to bring the benefits of its advanced companding technology to smaller studios and semi-professional users. Designed for use with open-reel multitrack tape recorders from manufacturers such as TEAC, TASCAM, and Otari, the dbx 155 offered true broadband noise reduction in excess of 30dB, coupled with an additional 10dB of usable headroom. It delivered the company’s trademark linear 2:1 compression during recording and 1:2 expansion during playback, effectively eliminating tape hiss and extending dynamic range across the full audio spectrum.
Unlike competing systems that relied on pre-emphasis and multiple filter bands, the dbx 155 used a full-band RMS-sensing compander, ensuring accurate encode and decode tracking regardless of phase shifts or frequency content. This approach not only maintained transient response but also avoided the audible artefacts of other systems, such as pumping or breathing. Each of the four channels on the dbx 155 could be independently switched between record (encode), playback (decode), or bypass, allowing for maximum flexibility in professional and semi-professional studio applications.
Connectivity was via RCA phono inputs and outputs, supporting +21dBm maximum levels with 50kΩ input impedance and 100Ω output impedance. The dbx 155 featured modular circuit boards for each channel, making servicing and replacement straightforward. It also included adjustable front-panel level controls for both record and playback modes, simplifying setup with different tape machines and signal levels. Its compact 3½-inch-high chassis could be used as a tabletop unit or rack-mounted using an optional kit, with two units fitting side by side in a standard rack width.
The dbx 155 maintained a frequency response of ±1dB from 30Hz to 20kHz through the full encode-decode cycle and offered a total harmonic distortion of just 0.5% with typical intermodulation distortion of 0.15%. Power consumption was 10 watts, and the unit’s rugged steel construction made it well suited for regular studio use. dbx marketed the dbx 155 as an ideal solution for musicians, studios, and audiovisual facilities seeking professional noise-free recording and playback without the need for calibration tones or complex setup procedures.
Features
- Four independent noise reduction channels for record or playback
- 30dB broadband noise reduction and 10dB added headroom
- True RMS detection for accurate encode/decode tracking
- Linear 2:1 compression and 1:2 expansion over a 100dB range
- No pilot tones or calibration required
- Front panel level adjustments for record and playback
- Modular circuit boards for each channel, easily replaceable
- RCA phono input and output connectors
- Optional rack-mounting kit for one or two units
- Designed for compatibility with TEAC, TASCAM, and Otari tape recorders
