Tongue-twister

 "John's just dressing," Jenny joked.

This is the j sound we get in jam and jumper; I contrasted it with dressing because you need to work harder to contrast than to do all the same sounds.

/ʤɒnz ʤʌst dresɪɳ/  remember, in just John, etc, the initial sound is voiced, the vocal folds vibrate, while at the end of just you have a voiceless /t/. However, we tend to run the t and the next d into each other to make /ʤʌs dresɪɳ/ 

Remember,  j in English isn't pronounced like ch in church, but like judge. 

Try this exercise: Put your hands over your ears. Say the word church. Then say judge. You can feel a vibration at both ends of the second but not the first.