
I'm not up on the details of US patent law, but I think this is incorrect.
There is a "reasonable use" exemption for *copyright*.  There is none for
*patents*.  The exemptions from patent licensing are quite narrow; R&D work
is exempt but personal use is not.  That is, it's okay to experiment with
a patented idea, but not to put it to practical use (e.g. to improve your
stereo), even if it's only your own private practical use.

Of course, it is unlikely that discreet personal use will ever be detected
or that you will ever be sued over it.