Does a probation officer have the say so as to what happens to you if you violate your probation? Or is it up to the judge?

The ultimate decision as to whether your probation will be revoked is up to the Judge. But in making that decision, the Judge will rely heavily upon the probation officer's recommendation. You will have the right to a hearing and to present witnesses and your side of the story. You can cross-examine any witnesses called by the prosecution. You can contest the allegations against you and show the Judge that you did not violate your probation. If you did violate the terms of your probation, you can present your reasons as mitigation, so that the Judge may decide to give you another chance and continue your probation. If your probation is revoked, it's a serious matter. The Judge may sentence you to any term of imprisonment provided for the charge to which you pleaded guilty, less credit for time already served. A prosecutor will be presenting the case for revocation to the Judge. I recommend that you retain an experienced criminal defense lawyer in your jurisdiction to present your side to the Judge in the most favorable light possible.