@Phil, @Keith Phil is right. One of the characteristics of English is that vowels are lengthened before voiced consonants (Example: <beet>[bit] and <bead> [bi:d]). This is buried in some of my linguistics books, but it is specifically mentioned in the pronunciation book "English Pronunciation Made Simple" when introducing voiced/unvoiced exercises for final plosives ([b]/[p], [t]/[d], [g]/[k]). Thus <bead> has both a lengthened vowel and a voiced final consonant. I remember reading phonetics research reports that English speakers are more sensitive to the length of the vowel than to the voicing of the final consonant.

Yes and no. In English, “voiced” consonants are not as fully voiced as in Latin or Slavic languages. Native speakers try to help, but most actually have no idea how they pronounce their own language. They’ll tell you to do it one way, when in fact they do it another. The most important difference between words like “etch” and “edge” is that the vowel is shorter in “etch” and longer in “edge”. In English, this is generally true of so-called unvoiced and voiced consonant finals, for example belief / believe, wet / wed, etc. Pay attention to how native speakers talk when they’re talking naturally, NOT when they’re demonstrating “proper pronunciation”.

‘Merge’ has a ‘j’ sound at the end, as in John, whereas ‘merch’ ends in the ‘ch’ sounds, as in ‘chips’. Try saying ‘mer-john’, extending the first ‘er’ sound, then cut off the ‘ohn’ of John.

@Evelin Yes. The sounds are different and the difference is meaningful in English. English has about 45 sounds (phonemes) compared to about 30 for Spanish. As a Spanish speaker, your brain will "convert" an English sound to the nearest Spanish sound unless you get some training to recognize English sounds. A teacher with a background in linguistics can help you master English sounds in a short time. With Youtube or a conversation partner, you can master the sounds, but at a slower pace.

They are different: j and ch J is a soft or slow version of ch like D is a soft or slow version of T. (That's why Phil thinks the vowels are shorter and longer)