Hi. I think "schwa" is not actually a phoneme as everyone says. It seems to me like an area in the IPA vowel chart. Sometimes you can use /ɜ/ and others /a/ instead of "schwa".Some websites say you can change for /ʌ/. I´ve read many websites and nobody agrees but I´m sure "schwa" is not always the same sound.
I see "schwa" simply like an unstressed sound. Nothing more.
Personally I move that phoneme to /ɜ/ often.
Greetings and sorry if I made mistakes in my english.