The invention provides a compound of formula (Ia), and pharmaceutically acceptable salts thereof. The invention also provides use of the compounds or salts as modulators of Kv3.1 and/or Kv3.2, and in the treatment of diseases or disorders where a modulator of Kv3.1 and/or Kv3.2 is required, such as depression and mood disorders, hearing disorders, schizopherenea, substance abuse disorders, sleep disorders or epilepsy.
