Hi-Fi Fadeout by Carter Brown

Hi-Fi Fadeout was published in 1958 and features character Mike Beck. Mike is a DJ fora top rated radio show called The Midnight Rocket to Fame. A fellow DJ is in competition with him. Her show happens to follow his and his boss wanted Mike to make friends with her. He leaves her dead in his car and is the prime suspect in her murder.Everyone is against Mike, even the redhead who persuaded him to play her record with a gun. Then there are the thugs and three pretty young ladies  on him all the time. So Lt. Voss offers protection in the shape of brunette Officer Regan. Hi-Fi Fadeout is number 70 in the Numbered Series published by Horwitz Publications.