"Somebody just came and dropped off this whole bag of cassettes," Jim Hopkins says, showing me a plastic grocery bag full of hand-labeled tapes sitting in the corner of the DJ booth at 440 in the Castro, where he is the midweek resident. He's recently been working on a new project, the SF Disco Preservation Society, and he's taken on the somewhat thankless but admirable task of transferring two decades' worth of club mixes from local nightlife luminaries like Larry Reed, Ellen Ferrato, David Harness and others from analog tape to digital, and uploading them to his website where you can now listen to them — and work out to them — for free. "A lot of these guys are getting up in years," Hopkins tells SFist, "and this is stuff that shouldn't be lost."

The art of the club mix — equal parts curation, imagination, and rhythmic skill — is something that's evolved over the decades in different ways in different cities, with DJs finding influences both locally and internationally. But before the explosion of file-sharing in the early 2000s and the widespread accessibility of digitized music a few years later, DJ sets were things you only ever experienced live in the nightclubs themselves, unless your friend was a DJ and copied a cassette for you — or unless that DJ was famous enough to have a record label and a few CDs.

Hopkins wants people who went to SF nightclubs like Pleasuredome, the I-Beam, and the EndUp back in the day to be able to hear some of these multi-hour mixes that they may only have the haziest memories of, and he wants to introduce a new generation of DJs and nightlife mavens to the talents of their forebears.

Hopkins is also trying to preserve San Francisco's place in disco history. "Clubs such as The Trocadero Transfer, Dreamland, City Disco, and The I-Beam were the places to hear the best disco music," as he told SF Weekly in an interview last fall, adding that the city has "always maintained a tradition of high-energy dance places" which continues today.

He recalled for SF Weekly how he saw his first DJ, in a mirrored, octagon-shaped booth, at a disco in Roseville, California called Marmalade Max, when he was 13 in 1978. From there, he convinced his dad to buy him two turntables and a mixer from Radioshack, and soon he'd be spinning in and haunting the clubs in San Francisco.

The SFDPS also has a Facebook page with a trove of amazing historic nightlife photos and nightclub flyers.

So far there are a couple hundred DJ mixes uploaded to the 1980s and 1990s sections of the SF Disco Preservation Society website, all downloadable and embeddable using the HeartThis app, and available to stream for free.

This all started when Hopkins bought an old reel-to-reel deck a few years ago and answered an ad from a woman whose dad was a DJ and who had a bunch of old reel-to-reel tapes she wanted digitized. She couldn't pay to have it all done, so Hopkins said he'd do it if he could keep the tapes in return.

Says Hopkins, "[I'm] always looking for rare DJ mixtape collections on reel-to-reel, and cassette, to preserve and archive to digital for future generations." And he adds that if you have a collection, he'd also be happy to borrow it, digitize it, and return it promptly.

A few more fun examples below.

Related: Does Anyone Go Out Anymore?: San Francisco Nightlife In The Age Of Netflix And Chill