Schwa /ə/ is a phonetically variable sound. It may be [ɪ̈]-ish (or reportedly even [ɨ]-ish), depending on position and dialect, while oftentimes it is [ə] (or [ɘ] in New Zealand English), and for at least some dialects it can be [ɐ]-ish (or even [ä]-ish; not a native speaker) word-finally and before plural and possessive /s/ ('-er' too in some non-rhotic dialects). Before [ɫ], it may be (near-)back, precisely [ɤ]-ish or [ʌ]-ish, which is evidenced by misspellings in which 'e' (representative of /ə/), 'u' (for some speakers; representative of /ʌ/), and 'a' (representative of /ɔ(ː)/) are confused before [ɫ]. It can be voiceless in some words too. I wonder if anyone noted that variation, and if so, if it has been properly studied.
In a comment John Lawler wrote:
Yes. Schwa is the only central vowel phoneme in English. In American dialects, it's lowered to [ʌ] when stressed, and its allophones vary all over the central vowel space when not stressed. That's because there are no other central vowel phonemes that it contrasts with, so individual variation is normal and unremarkable. Front and back vowels contrast strongly in English (2 high front, 2 mid front, 1 low front, 1 low back, two mid back, two high back), but there's only the one central vowel.