How do you know when an LP is a first or early pressing?

mglik, it can go either way. Although the masters may be better back in time popular records often got cut short in pressing quality. A good master with top notch modern pressing technique and premium vinyl can yield a superior result. This does not take into account that most popular records were not taken the best care of. I personally will not buy used vinyl. I have thousands of old records. I do not need any more. Some reprints are actually far superior to their original versions because the original masters were terrible. A good example of this is the early Roxy Music records. The 1/2 speed remastered versions are worlds better than the originals. Some of Frank Zappa's early catalog were mastered on second rate systems. Before he passed he remastered several of them with exceptional results. Far superior to the originals. 

The site is down. If they're left coast the inventory could be melted.
Awww

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+1 Discogs. Great resource.

I’ve cataloged all my physical media on Discogs. Takes much time (depending on how many you have) but worth it.

But also agree that not all first pressing are the best, even though they might be worth more in some cases. Many times a reissue/remaster can sound better. It just depends.

On the subject of reissue/remaster, I have found that the best reissue/remaster copies sound phenomenal when the right people did the mastering, and the pressing and vinyl quality are first rate.  You have to research to find who did it and who pressed it. I have also been very disappointed with some reissues, particularly those that are sourced from digital files.  The Pink Floyd reissues, on Pink Floyd Records, are fine examples of excellent mastering and pressing.  Impex does a phenomenal job, I highly recommend the Jennifer Warnes latest reissue of Famous Blue Raincoat and produced by Impex.  It's stunning!  The list goes on, but I believe that you get the idea.  Originals, as others have said, can be a crap shoot.  Unfortunately that is indeed the case with originals, just as it is with reissue/remasters.  

So, Really this just comes down to treasure hunting? I have been buying vinyl for the last 10 years. Great sounding vinyl can come from a forty year old Verve record that you found in a used record store, or a fantastic sounding copy of Steely Dan's Aja on ABC records at the Antique mall, or a very good sounding new copy of Eric Clapton greatest hits from RTI. The Austin record convention is a fantastic place to find rare things and of course its all hit or miss!


Matt M