Fourier Components OTL Amplifiers

Tom Gambill, the founder of Fourier Components, had a vision of making excellent high fidelity equipment. When the patents on the Futterman OTL amps expired, several companies including Fourier Components started making "clones". It was clear that the power output, reliability, and use of easily-available parts could be improved, though. When Tom was living in Morgan Hill, California, he got in touch with me through the Bay Area Tube Enthusiasts group to help him with these improvements.

We worked on various improvements to the Futterman design resulting in the Sans Pareil (French for "without parallel"), including: higher power through the use of ten instead of eight output tubes, improved screen regulators, elimination of the hard-to-get 6HS5 and 6MU8 tubes, a power-on surge-supressor was added, and more stable biasing was implemented. With the "Mark III" design, a bias servo was added to the first stage and a toroidal choke was added in the main power supply. With the "Mark V" a full auto-bias circuit was added, among other changes.

After Tom moved to St. Peters, Missouri, I continued working with him on design improvements. I did a major design change to the San Pareil that replaced the beam-power output tubes with 6AS7-type regulator tubes. This resulted in the Triomphe stereo amplifier. The Triomphe circuit was modified by Tom to use the Russian 6C33C tubes, giving the mono-block Panthere amplifier.

Due to the vagaries of the high-end audio business, Fourier Components closed-down around 1996. As far as I know, there is no official follow-on for support of existing equipment. Here is my last contact information, as of February 1996:

Fourier Components, Inc.
116 Main Street
Saint Peters, MO 63376
Tel: 314 946-4232
FAX: 314 925-0800

I recently found some Fourier data, and will be putting it up on the web. Here are three brochures from about 1994:

Sans Pareil Brochure page 1 (picture), page 2 (specs).

Triomphe Brochure page 1 (picture), page 2 (specs).

Panthere Brochure page 1 (picture), page 2 (specs).

My involvement with Fourier Components was as a design consultant, mainly in the generation of circuit ideas and in helping solve technical problems. I was not part of the PC-board design, in-house design or manufacturing processes. As such, there were several areas where I repeatedly urged improvements: engineering documentation and ease of adjustment. To my knowledge, there were no official schematics - just scraps of circuit fragments. There isn't much I can do to ease the adjustment problem, other than provide clear instructions. However, as time permits, and as I have access to equipment, I am generating schematics.

The following schematic was extracted from a Fourier Components Sans Pareil Mark III, serial number SAN079501L. If you find any mistakes are changes, contact me at . Keep in mind that were many small variations between models and versions.

Sans Pareil Mark III (PDF: 117Kbytes)

The following schematic was kindly sent to me by Scott Nixon. It is a factory schematic of the Sans Pareil Mark I. Scott reports that it appears to be accurate. The readability isn't great, but these should help anyone working on a Mark I. The soft-start board is not on this schematic, but is the same circuit as the soft-start on the Mark III, above.

Sans Pareil Mark I, left half (GIF: 97Kbytes)
Sans Pareil Mark I, right half (GIF: 76Kbytes)

- John Atwood

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