You can manufacture a writing voice or use your own. It's the same for actors. Some use their own voice throughout their career (Hugh Grant, Liam Neeson), the rest choose method acting and pick the appropriate accent, style etc. (Meryl Streep, Christian Waltz).
The dilemma for all new copywriters is which to choose. My recommendation would be to develop your own voice (which takes time – so be patient). Your voice becomes your USP (you want people to say "no one writes copy as good as [insert your name]").
However, if you develop the ability to write in many voices, then you can use that to divide and conquer markets (getting copywriting jobs is the same as any marketing exercise – it's all about positioning you as Unique, Necessary and Irresistible).
If you do choose a multi-voice approach, please please please never use the "corporate voice" unless you're offered a lot of money (this is just a plea to save the rest of us from more boring and useless copy – thank you 🙂