What doppler do you have?

Dana
I need peace of mind so I think I'll purchase a Doppler. I'm 8w 3D and my first appointment isn't until 7/5.  It would be great to be assured before then. And in between appointments as well. 
I had a missed miscarriage before my son so I'm terrified of first appointments. I can't relax and enjoy this. 
What kind do you have and how early could you hear the heart beat?