Marc:
In English (as opposed to, say, Dutch) it is important to distinguish voiced / unvoiced consonants even at the end of a syllable. Luckily, there are some tricks that native speakers use unconsciously — they’ll deny it, but you’ll hear it once you know what to listen for.
1. Other things being equal, the vowel before an unvoiced consonant sounds shorter than before a voiced consonant. If you say “believe” but shorten the vowel in the second syllable, people will hear “belief” even if you actually use a V, just because you clipped the vowel. The reverse is also true.
2. Voiced consonants generally have more friction than unvoiced ones. An unvoiced fricative will also tend to last longer:
belief / believe
/bəlɪiff/ /bəlɪiːv/
If you follow the preceding two rules, you don’t even have to worry about whether or not your English fricatives /f/ /v/ /θ/ /ð/ or sibilants /s/ /z/ /(t)ʃ/ /(d)ʒ/ are actually voiced or not — the illusion is nearly perfect.
Note: As you know, English and Dutch were the same language just hundreds of years ago (the blink of an eye), and the only time English speakers truly pronounce voiced fricatives and sibilants with full voicing is between vowels. (Just be careful, as a Dutchman, not to prolong the V too much at the beginning of a word, or it will sound like an F.)