VINTAGE SANYO SUPER D NOISE REDUCTION/COMPANDER ADAPTOR - SANYO PLUS N55

Description

What does it do?
"SUPER D - THEORY OF OPERATION
Cassette tape decks are popularly used today among audiophiles for sound recording and reproduction. Despite their many excellent performance characteristics, there are some problems which have remained unsolved. Of these the most notable one derives from the slow tape speed and the narrow sound tracks, which make it difficult to tape record and play back record music, FM. broadcasts, live performance and sound existing in the natural world with a superb SN ratio and without sound distortion over a wide dynamic range by cutting noise at the small sound level and by eliminating distortion due to saturation at the large sound end. By the combined application of the level compression-expansion techniques and the newly developed complementary band divider, the. SUPER D system of SANYO compresses (encodes) sound signals in the recording process and restores them to their original condition by expanding (decoding) them in the playback process This is accordingly, a kind of the compander system...
The SANYO SUPER D (model PLUS N55) unit, when adopted expands the dynamic range of a cassette tape deck approximately 100 times (by about +40 dB) wider than when it is not in use. At the same time, noise can be reduced to about 1/100 (by about —40 dB). Thus clear high-fidelity sound can be reproduced over a very wide dynamic range. Meanwhile, the breathing phenomenon (i.e. noise fluctuations due to changes in signal level) in the actual application of the SUPER D system has been reduced to an imperceptible level by incorporating into it a complementary band divider." - from
Sanyo Plus N55 Super D Noise Reduction System Operation Service Manual
Purchased at the Bonn, Germany PX in the early 1980's.
This is the European model with selectable 115V/220V  current input and with US plug adaptor.
Powers on and calibration signal shows on display.