Hey, I know sometimes audio can get frustrating. I amgoing to ask you to bring your questionable records to an audio store or a friends house whose system sounds good. This could be a setup issue even if some newer pressings sounds good. It does not matter if the cartridge was pre mounted unless you are using a conical stylus (circular). Do not give up. Some past recordings and even raw materials were not great. For some reason I get this weird error code when I try to look at members systems. It could be that your old vinyl was thin (120g) and your new vinyl is thicker (180g). By lowering the pivot point of your tonearm it creates more bass from the weight (VTF) of your cartridge. Find a second platter mat or put two of your old records you do not care about and put them both on the platter and play the top record. If you feel it improved then it is a VTF (cartridge weight) issue.
Old records.
I’ve been literally keeping my somewhat recently bought turntable (and accessories) on the shelf and not using it after spending a lot on it (for me.) ( You can take a look on my profile)
After comparing it to my digital side for quite a while I decided the SQ was not nearly as good. So, I put the cover on it and let it lay dormant.
Now I have a collection of about 3000 LPs, mostly from the 70’s and 80’s. And, sad to say, most of them just don’t sound that good. However I’ve recently been playing some newer records, and the sound is wonderful. I know this not supposed to be the case. So, it’s possible all my old records have been somewhat damaged with old or faulty styli. Anyhow I now have a new lease on life with my analog side.