TAKEN FROM wikipedia
http://en.wikipedia.org/wiki/Schwa

In English, the SCHWA sound is considered the equivalent, or
ALLOPHONE (SEE BELOW), of "no vowel at all."

ALLOPHONE
In phonetics, an allophone is one of several similar phones or speech sounds, that belong to the same phoneme. Each allophone is used in a specific phonetic context.

For example, p as in pin and p as in spin are allophones in the English language. English speakers generally treat these as the same sound, but they are different. The latter is unaspirated: it sounds a little more like the b of English. The preceding s is the usual context for the unaspirated allophone.

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So, it seems the ever elusive SCHWA sound can vary slightly depending on the
specific phonetic context in which it is used. Hmmm... I personally do not believe
in the SCHWA sound. It's a myth like Santa or the Easter Bunny or Tooth Fairy.
Just because we can say it's name does not mean it exists - well, other than on
the edge of our tongue & vibration of our chords - D SCHWA H!!!