MDF 777 vs. Littmann lightweight

I was considering buying a new stethoscope because when I listen to older patients with my MDF 777 the sound isn't as loud, but it has great sound when listening to my own heart. I was considering littman because of the brand and thought it would be better. I know the Littmann cardiology is the best but I don't want to spend a lot of money because I am just a student right now, but I want a good quality stethoscope.