This series contains Hellmuth Wolff’s correspondence files. Subseries i contains correspondence between Wolff and various organ builders in English, French and German, primarily related to Wolff’s editorial work for the for the International Society of Organbuilders’ ISO Yearbook 1993, which spanned four years from 1992-1996. Subseries ii contains workshop documents, including opus lists.

This series contains various temperament specifications.

The photographs in this series cover the several stages of the organ-building process. This series includes both colour and black-and-white images of the construction of a given organ at Wolff’s atelier, the installation of the organ, as well as concerts, dedications, and social events at or around the time of the organ’s installation.

This series consists of photographs with Sonde event number indicated if known.

The documents in this series include posters for concerts, several of which were given on Wolff’s instruments, as well as drawings and sketches of Wolff organs. These documents are not rolled like the organ plans in Series 1 but rather are spread flat

This series consists of background information about Sonde and biographical sketches of its members.

This series includes large-scale drawings, preliminary sketches, and general plans of various parts of the organ, such as the buffet, console, keyboards, and windchest. This series is divided into three subseries: organs with opus number; organs without opus number, which includes Wolff’s plans for proposed but ultimately not-constructed organs; and finally plans by other organ builders or Wolff’s drawings based on historical treatises and documents.

This series contains published annual calendars from three European organ builders.

The Photographs series contains biographical and professional photos of Paul Pedersen alone and with others, as well as miscellaneous photos and proof sheets.