I am sorry to hear about your cat scratching this much. My name is Rebecca. I am a veterinarian and will do my best to help.
Allergies, particularly food allergies, are a reason for cats to scratch their face, neck and ears to bleeding. Food allergies are usually to one or more particular food ingredient, usually fish or meat protein, and just changeing the diet may not change what he is actually eating. If food allergy is suspected, you try either a limited ingredient diet with only one meat protein, and that has to be something new for him, such as a rabbit/ green pea diet, or else a "hydrolized protein" diet from your veterinarian.
Ear mites are another cause, and there are also another species of mite, skin mites, that can cause this. If this were my own cat, I would give a cortisone injection and put Revolution on him (control some mites as well as fleas and ticks), do skin scrapings to look for mites and ear swabs to look for ear mites under the microscope (you can't see mites with the naked eye), and start a limited protein diet.
Let me know what other questions I can answer.