I'm joining this thread a little late (only read the digest version every few days or so), so pardon me if you already have covered this. There were no quad turntables per se (except those hawked as such at the very low end). For CD-4 quad LP's (championed by RCA) you needed a cartridge with response up to 45,000 - 50,000 Hz, many coming with a special cut to the actual stylus (Stanton called theirs 'quadrahedrial' IIRC, and there was also the Shibata stylus). The quad channels were physically encoded on the record, and you needed the cartridge and a CD-4 demodulator, either as an add-on unit, or built into a receiver. I vaguely recall a TT or two with a demodulator built in, but they were rare. Marantz, Harmon-Kardon, Panasonic, and Pioneer all made demodulators. The demodulators come up frequently on eBay, and there's a guy on eBay who still sells new CD-4 cartridges. And TT's are still available - new ones can run from a few hundred for something decent to literally $10,000 and up (honest!) with the average high-end TT being between $800 and $1200. For once, eBay is reasonable and can get you something decent for between $100 and $200 (if you know your TT's). The two major matrixed (electrically encoded) systems were CBS-Sony SQ format and the Sansui QS format. The first decoders did only a little more than presenting a L-R 'ambiance' signal (the Dynaco Quadaptor did this without needing two additional amplifier channels), but partial front-back logic and then full-logic decoders were developed to provide greater separation. Electro-Voice also had their own matrix, but switched over to being compatible SQ when they saw which way the wind was blowing. The SQ matrix encoding is still the basis of the multi-channel home theater systems you buy today. A little web-searching will find you many quad sites. Bob Stek Saver of Lost Sols (and old quad equipment)