Phil is an expert in this area. Trust his answer.

In my opinion, those are two entirely different phonemes (even if /ə/ *sometimes* sounds like /ʌ/). My advice is that you *not* conflate the two. /ʌ/ is an ordinary vowel found in stressed syllables, while /ə/ is a reduced vowel that is only found in unstressed syllables. The schwa is the most common sound in the English language, and is the “secret” to sounding “natural” (and understanding native speakers), so learn it :)