How does one pronounce loch? I understand this is a term borrowed from the Scots. Dictionaries are not very helpful with the last syllable. What is the closest English mapping of ch?
In Scottish English, it is a voiceless velar fricative /x/. In other dialects, it is realized as a voiceless velar stop /k/. That's how all foreign sounds are nativized--this is called loanword phonology in the literature.
Dictionary.com says that it's pronounced lok or logh (try listening to the audio clip; it will help you understand what I mean by logh).
Your problem is that there is NO direct equivalent in normal English pronunciation.
I can agree that it can sound affected to try to follow too closely the native pronunciation. I say 'Chile' not 'Chilay' and 'Paris' not 'Paree'.
It is 100% acceptable to pronounce 'loch' just as 'lock', but I think that I do tend to soften it just a little, ending in that 'chh' sound rather than the hard 'k'.