Sony ST-S555ES
(1983 - 1987)

The first ES tuner : a favorite in Japan back then, just below Kenwood's L-02T :-)

But the 555 had one thing really different and that was ACT : Audio Current Transfer. Instead of transmitting the audio signal to the amp in the form of voltage, it used current.

Can you hear the difference? Most definitely !... said the litterature. Also, it used the famed Direct Comparator circuit (CX778), directly responsible for a stunning s/n ratio and which is used on Sony's tuners until... the late '90s.
ACT needed a mini-DIN plug on the tuner side and a regular pair of plugs on the amp/preamp side with a sort of box in between the two - a rare accessory these days...

Sony's top FM tuners are quite often not very much talked about but they deserve non-slanted sonic comparisons - they generally slash a lot of what is out there - ST-A7B, ST-A6B, ST-5000, ST-5950SD, ST-S730ES.

"For the price of an average tuner a few years ago, you can now own one of the all-time greats - the Sony ST-S555ES" (said the litterature).