Cult classic quasi-surround sound processor using the Hafler circuit. Gets great results on a variety of standard stereo recordings.

Here’s a 1999 review from Primyl Vinyl, which was already looking back at a vintage piece:

The QD-1/IIL is a well-made little box (about the size of the Audio Alchemy stuff), and it retailed at a very reasonable $90. I remember quite complimentary reviews of it in the audio/video mags. Imagine my surprise when I saw the little devil advertised on the back page of the New York Times’ Arts section…for would-ya-believe $19.95. We are talking close-out countdown here, so get cracking–I presume J and R Music World bought up the remaining stock. Naturally, I ordered one up, and strapped it into the system. Nothing fancy, some Radio Shack 18ga. and my old Spica TC-50s some 6 feet behind the couch. (I aimed them at the sidewalls to fully diffuse the ambient sound–you might try box speakers aimed up at the ceiling. Great reason to buy Bose at the next yard sale, too). I set the gain so the rear speakers were not quite audible as independent sources.

The results were interesting in the extreme, although varied from record to record, genre to genre. As expected, SQ/QS recordings came through beautifully, although with somewhat less "localization " than I’ve heard from active matrix decoders. What was most satisfying was the degree of enhancement on many (but not all) straight stereo LPs and CDs. What worked best? Minimally miked classical (Decca, EMI, Mercury, RCA etc.) acquired a sublime sense of "being in the hall" that simply eclipsed 2-channel replay–immersion in the ambient soundfield really opens up the stereo imaging, particularly the sense of depth. Same with live recordings in general–Dan Hicks’ Where’s the Money awoke aural memories of hanging out at the Troubador as never before. Sound tracks "designed" for cinema surround were a big success–things like Glory, The Emerald Forest, Ry Cooder’s "ambient" guitar work on Alamo Bay and Paris, Texas. Jazz recordings were more variable, but ensemble and staging was usually more coherent. Live FM was fabulous. What didn’t work? Multi-tracked, overdubbed anything was usually no better, sometimes plain odd; in-studio processing, I presume. Bottom Line? The QD-1/IIL has got to be the most amazing $20 little black box you’ll ever add to a stereo system! Get 'em while you can, and enjoy some ambience with the music.