Little is documented about the Advent DBX-117. Even the model name is uncertain. Period publications refer to a "dbx 117" unit, and the available record doesn't confirm whether it was sold under the Advent brand or was a separate dbx-branded product. The magazine references describe a dynamics processor, called both a Dynamic Range Enhancer and a Noise Reduction Unit.
Audio (August 1975, p.82) stated the dbx 117 could restore up to 20 dB of dynamic range. An earlier report in HiFI/Stereo (December 1971, p.73) gave measured performance for a "Model 117". Harmonic distortion was 0.05% at a 1-volt output for most settings of the Expression control, rising to 0.6% at a control setting of 1.4 and 1% at 0.7. Output noise varied widely with the control setting - 56 dB below 1 volt at the 0.7 setting, improving to -69 dB at other positions. The same review noted that careful adjustment could make the compression/expansion completely undetectable while still achieving impressive noise reduction. One limitation: you lose off-the-tape monitoring when using the unit.
High Fidelity (July 1975, p.24) observed that with the unit set for moderate expansion, music had more impact and recordings seemed more noise-free. At extreme settings it exaggerated dynamics noticeably. A classified ad in Audio (October 1979, p.166) offered a modification that brought "BI-FET" circuitry to the DBX 117 and 119, which suggests an aftermarket upgrade path existed for these units.
Beyond these period fragments — a handful of measurements, a functional description, and a mention of modification — almost nothing else survives. No production years, original price, dimensions, or service documentation have been located. The Advent DBX-117 (or the dbx 117 associated with Advent) remains a scarcely recorded entry in the dynamics-processor market of the early 1970s.
- Type: Dynamic range enhancer / noise reduction unit (compander)
- Distortion (20 Hz, 1V output): 0.05% at Expression setting 1; 0.6% at 1.4; 1% at 0.7
- Noise (below 1V): 56 dB at setting 0.7; −69 dB at optimum settings
- Dynamic range restoration: up to 20 dB claimed
- Noted limitation: disables off-the-tape monitoring
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