Name: Advent 100A
Brand: Advent

Not much is documented about the Advent 100A beyond its period reviews. What the record shows: it was the refined successor to the Advent Model 100 Dolby noise-reduction unit, with engineering changes “designed to match it to every likely Dolby application now and in the future.” Audio (May 1972, p.41) announced the 100A in an advertorial. It noted that the original Model 100 had been “the fullest and most flexible version of the Dolby System for home use” for two years, and that the new version brought unspectacular but important switching improvements. High Fidelity (April 1972, p.32) confirmed that the 100A had “more flexibility of switching and application” than its predecessor. The big addition was the ability to handle signals - from tape or FM - that were already Dolby-encoded. You could, for instance, make a Dolbyized copy of a Dolbyized tape using the 100A’s circuitry only for the monitored signal.

The front panel offered two mixable stereo line inputs. There were no built-in microphone preamps, but an optional MPR-1 stereo microphone preamplifier was available for $20. It plugged into one of the line inputs and accepted balanced microphone cables. All connections on the rear were RCA jacks in left/right pairs: line‑1 input, line‑2 input, output to tape deck, playback input from tape deck, and output to the stereo system. Both input pairs could be adapted for microphones. The Dolby switching let the unit encode or decode Dolby B noise reduction. Signals from the stereo system were normally Dolby-encoded as long as the noise-reduction switch was set to “in.”

No service manual or detailed production figures survive. The 100A appears to have been a transitional model - it refined the Dolby home unit concept just before Dolby B became widely built into cassette decks and receivers. Its price was not recorded in the available reviews, but the earlier Model 100 sold for $250, and the 100A likely hovered in that range.

Type: Dolby B noise reduction unit (encode/decode)
Inputs: Two line inputs (mixable), optional MPR‑1 mic preamp
Outputs: Tape deck output, playback input from deck, line output to system
Connectors: RCA jacks (all pairs)
Dolby compatibility: Encode/decode with switchable bypass for already‑Dolbyized signals
Optional accessory: MPR‑1 stereo microphone preamplifier ($20)
Period reviewed: 1971–1973