This is considered to be a masterpiece which was made at the height of Spanish baroque organ making. It was built by organ maker Lorenzo de Arrázola, a resident of nearby Oñate. Juan Antonio de Maíz and Joaquín Antonio de Berasategui were the wood carvers charged with building the great organ case, in accord with the dimensions laid down by the aforementioned organ maker. It cost 12,000 reales de vellón. On the organ face an inscription reads: LAUDATE DNM. IN TIMPANO y CORO LAUDATE EUM IN CORDIS y ORGANO.
It was restored by José Maria Arrizabalaga in 1996.
It has a single keyboard (manual) of 45 notes with a short (C-c´´´) octave and another Contras pedal (C-H). It has 35 divided stops: 15 for the basses and 20 for the trebles. Its temperament is based on the Herbert Anton Kellner’s reconstitution of Bach’s well-tempered tuning. Particular mention can be made of a stop known as Flautado de Ecos that functions in a manner that was later to become characteristic of the Swell Organ of the romantic period instruments.
