What is the difference between /ʌ/ and /ə/?

Question

In this Wikipedia article in the section talking about the use of schwa in Indonesian and Malay, they use /ʌ/ instead of /ə/ to write the words that have a stressed schwa.

Also the pronunciation by native speakers of some words in English, for instance done or must, sound very similar to me as if they were pronounced like other vowels than /ʌ/.

/dʌn/ sounds similar to /don/

/mʌst/ sounds similar to /mʊst/

This make me thing that /ʌ/ is like /ə/ in the way that it is a reduced vowel, but the difference is that the former is used in stressed syllables. So how can I know the difference between the sounds of /ʌ/ and /ə/, if I want to pronounce both as a reduced vowel? Do I need to pay attention only to whether the syllable is stressed or whether it isn't to pronounce each sound?

The audio files for those words come with this application, but there are more than 2400 audio clips and I couldn't find the clips for done and must in the application's package, but I found the one for flourish, that has the transcription /ˈflʌrɪʃ/ but it sounds to me like /ˈfləʊrɪʃ/

Answer 1

Those sounds are not always easy for learners to distinguish. But there are two differences to note.

First, they're articulated differently. /ʌ/ is low-mid / back / unrounded. /ə/ is mid / central / unrounded (in English). Hence, /ʌ/ is further back and slightly lower.

Second, many dialects of English use /ə/ only for reduced vowels, which have interesting behaviour, such as dropping out or being replaced by syllabic nasals. Compare sadden /ˈsædən/ and unkind /ʌnˈkaɪnd/, where the vowels we're looking at are each in an unstressed syllable. It's possible for the /ə/ in sadden to drop in favour of a syllabic /n/, but the /ʌ/ in unkind can't drop.

However, a few dialects of English make use of /ə/ in stressed syllables, though that article says it's "often transcribed" as the very close /ɜ/. You could tune your ear by the pronunciation of bud in North American English vs. bird in Received Pronunciation. They're similar, but not identical.