bluecafe1:Well, some older cd's have a low sound quality and by that I mean you'd have to crank up the amp to get a decent volume. Then some cd's that have been re-mastered (which in my opinion is a rip off, why haven't they been mastered properly in the first place?) don't need the volume on the amp as high. Sound qualityis better too.
Having to turn the volume up higher is not an indication of poor mastering or poor sound quality - quite the opposite normally! The wider the dynamic range (i.e. the difference in volume between the quietest and loudest sounds) of the material recorded on the disc, the higher you'll have to turn up the volume to get sounds like voices at the required level; everything else is then in proportion, although you'll find that the lound parts of the recording hit harder and higher reletive to everything else - precisely as they should.
One if the biggest enemies of sound quality at the moment is the modern trend of applying masses of dynamic range compression to recordings and remasters, designed to make tracks sound louder and therefore more attention grabbing and exciting on low quality replay equipment or in noisy environments, such as in cars, portable radios, all-in-one ipod docks etc etc. The whole dynamic range of the material is squashed into a narrow band which is just unrealistic and sounds worse on a decent set-up.
One brilliant example I have of this is a CD of Rumours by Fleetwood Mac. On The Chain it starts off really quietly and I have to crank the volume to almost twice as high as I would normally have it, but when I do it sounds great and when the kick drum kicks it really punches and the bass guitar vibrates through your chest.