I've skimmed through this thread, and will comment on a couple of things in the original post
- The turntable, Pioneer Rondo 3000, is an entry-level 1970's. I recall the Pioneer Rondo 3000 stereo system being heavily advertised on tv, being marketed as an upgrade from low-quality record players. It is similar quality to my first turntable, quality of reasonable reproduction, and when setup correctly won't damage records! The cartridge is probably OK for the quality of the arm/tt, but nothing very special. Your turntable is capable of OK enjoyable sound, but is not capable of high-end sound, so don't expect it to do so. I'm not putting it down, I enjoyed my equivalent turntable for years, until I upgraded. When I did upgrade I waited a few years so I could afford something that was much better quality, and looked at it as a long-term investment. That upgrade produced a significant upgrade in quality from the entry-level. If you are careful, you can get some excellent vintage turntables for much less than an equivalent quality new TT.
- If you are comparing your recordings of records to CDs, the compression added to the mastering will produce a different sound. This has been mentioned before, but I will elaborate. Compression reduces the dynamic range - it reduces the volume difference between the softest and loudest sounds in the recording, so the volume becomes more even. This can make it sound more detailed (the quite sound is increased in volume), and more exciting. However, listening to compressed music over time becomes fatiguing, and the music becomes less engaging. Your record recordings are likely to have bigger dynamic range (which is good). However, comparing to a compressed recording, especially for short periods in a an a-b comparision, the record will sound thinner and less exciting. Your recording will probably sound much better when you listen to the entire recording.
- The phono preamp will also influence the quality of the sound. Upgrading this when (or after) you upgrade your turntable will also be advisable. The one you have isn't too bad, better than a lot of cheapies, but could be better.
- Different masterings and mediums will have different qualities of sound. Different masterings of the same CD will sound different, and they will sound different to different masterings of the same music on LP. An individual record will have different qualities when played on different quality turntables. Putting aside mastering choices that can make the music sound worse (eg. compression, poor eq, etc), these differences may not be good or bad, just different.