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Big Briar Series 91

Designed by Bob Moog, the Big Briar Series 91 theremins were produced from 1991 to 1997. Series 91 are still played by Japanese thereminists Masami Takeuchi and Hiroshi Takano, by german thereminist Carolina Eyck and by U.S. thereminist James Coleman. Since they are no longer in production, the information below, taken from the Big Briar Information Bullettin No. 9201A, is presented only for historical reasons.

The Big Briar Series 91 theremins.
The Big Briar Series 91.

Big Briar Theremins

The Big Briar Series 91 theremins retain the timbre and playing characteristics of Professor Theremin’s design, but use contemporary digital and analog integrated circuit technology.


GENERAL DESCRIPTION: The Big Briar Series 91 theremins use contemporary solid-state digital and analog technology to implement the tone color and playing characteristics of the space-controlled instruments designed by Leon Theremin during the period 1930 – 1980. Several cabinet styles and interface options are available. All instruments of this series are designed by and built under the supervision of Robert Moog.

PITCH RANGE: Highest playable note is G6 (21/2 octaves above middle C), which is produced when the player’s right hand is approximately 1/2 inch from the pitch antenna. Any pitch below G6 may be produced. The lowest playable note is determined by how the player sets the Pitch Antenna adjustment. Most players prefer to set this adjustment so that a pitch between one and two octaves below middle C is produced when the player’s body is approximately 24 inches from the pitch antenna and the player’s right hand is at his/her shoulder.

VOLUME RANGE: Any volume level from maximum volume to complete silence may be produced. Most players prefer to set the Volume Antenna adjustment so that maximum volume is achieved when the player’s left hand is 12 Inches or more above the volume antenna, and complete silence is achieved when the player’s left hand is two inches or less above the volume antenna.

PITCH ANTENNA: Heavy-nlckel-plated straight brass tube, 19-1/2 inches long and 3/8 inch in diameter.

VOLUME ANTENNA: Heavy-nickel-plated loop shaped brass tube. Loop is approximately 13 inches long and six inches in diameter; tube diameter is 3/8″.

TECHNICAL DESCRIPTION: The Series 91 circuitry is divided into two separately operating parts: Control and Tone Generating.

Big Briar Series 91c theremin.
Big Briar Series 91c.


The control (antenna) circuitry consists of two specially designed antenna coils that form resonant circuits with the antennas themselves. The pitch antenna circuit is excited with a 263 kHz signal, while the volume antenna circuit is excited with a 461 kHz signal. The effects of the proximity of the player’s hands are measured by phase and amplitude detection circuits that are coupled to the antenna coils.

RESPONSE SPEED: Pitch and volume of tone respond essentially instantly (delay time less than two milliseconds) to the motions of the player’s hands.

Tone Generating

The tone generating circuitry uses contemporary analog synthesizer technology to emulate the waveforms of Professor Theremin’s instruments.

TIMBRES: A selection of four discrete timbres is available. Timbres vary in brightness, but conform to the spectral characteristics of Leon Theremin’s designs.

AMPLIFIER: A ten-watt amplifier for driving either the small internal speaker, or an 8-ohm extemal speaker, or both, is provided within the Instrument.

POWER REQUIREMENTS: 100-130 volts or 200-260 volts (switch selectable), 50-60 Hz AC, 50 watts. Power is applied to the instrument through an international standard three-conductor power line receptacle.


  • Volume Antenna adjustment
  • Pitch Antenna adjustment
  • Timbre selector switch
  • Power switch and indicator light
  • External audio (tone) switch
  • Internal speaker switch
  • Headphone jack; 1/8″ stereo mini-jack

POWER PANEL FEATURES: The power panel is located at the bottom of the instrument’s cabinet, and is readily accessible when the instrument is set up. It contains the power connector, power voltage selector, fuses, and audio, control connectors.


  • Unbalanced line level audio output
  • One volt/octave pitch control output
  • 0 – +5 volts volume control output
  • Speaker output

Instruments are designed to operate for many years with no internal tuning or maintenance.


OPTION ‘A’ -TRADITIONAL CABINET: Slanted-front cabinet similar in size and shape to instruments built by RCA in 1929, and by Leon Theremin during the period 1930-1938. Cabinet without stand is 20″ high, 19″ wide, and 12″ deep. Matching stand is 22″ high, 19″ wide, and 12″ deep. Stand may be taken apart for travel. Cabinet material is high quality walnut veneer. Finish is hand-rubbed lacquer. Color is dark brown.

OPTION ‘B’ – U-SHAPED CABINET:Similar in size and shape to instruments more recently designed by Leon Theremin. Cabinet without stand is 18″ high, 17-1/4″ wide, and 5″ deep. Matching stand is 24″ high, 18″ wide, and 10-1/2″ deep. Stand may be taken apart for travel. Cabinet material is hardwood plywood, veneered with black Formica.

OPTION ‘C’ – CONTEMPORARY CABINET: This interpretation of the traditional Theremin cabinet shape was designed by sculptor David McCornack in 1991. Cabinet without legs is 24″ wide, 20″ high. and 11″ deep. Legs are 28” long, and may be detached for travel. Cabinet material is highest quality cherry veneer. Finish is hand-rubbed lacquer. Color is that of natural cherry wood. Antennas are genuine gold-plated when Option C is selected.

OPTION ‘R’ – ROAD CASE: Rugged ATA-style road case with heavy-duty recessed hardware. Case is lined with 1″ foam.

OPTION ‘S’ – SMALL EXTERNAL SPEAKER: Heavy-duty, high-efficiency 6” speaker, mounted on a 16” square clear plastic baffle. Supplied with an adjustable tripod stand and connecting cable.


91AWalnut– $2500
Black– $2650
91 B– $2600
91 CCherry– $2900
Black– $3050
Walnut– $2900
External Speaker– $ 200
Roadcase for 91A– $ 375
Roadcase for 91B– $ 325
Roadcase for 91C– $ 595

[Copyright: © 1996 Big Briar, Inc.]

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