When can you hear baby with a stethoscope?

I have a stethoscope at home and wanted to use it listen to the babies heart beat. After trying for a long time at like 10-11weeks I realized it's too early LOL. I'm a little over 12 weeks and just impatient and nervous. I havent seen the baby since 9 weeks 6 days and won't until like 20ish weeks again. I worry a lot about "missed miscarriages" and this is my first pregnancy. I'm nervous to get a doppler because I heart to much use isn't good for baby.....

Soooo..... when do you think I can hear the heartbeat with the stethoscope? I'm impatient and overly worried obviously. Blaaaaaaah