Hi Keith,
In addition to all the above good advice,the way to extract the best sound from a cassette is to use a deck that lets you adjust the azimuth of the playback head. Unless you get lucky and find a deck that just happens to be perfectly aligned to your cassettes, you're going to lose some high-frequency content because of the misalignment. That said, it can be tricky but well worth the effort if you're comfortable with having a go. The tiniest of adjustments is all that will be required.
I wouldn't recommend this if you were going to use the deck for subsequent recording but I've found it to be invaluable for ensuring your high's aren't lost during playback of cassettes from different machines. Of course, in an ideal world all decks would be calibrated the same but even high end machines are not immune to a little azimuth shift!

Kind Regards,
Dave.

http://www.davemiller.uk.com
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