Ross . . . if your technician is good you might just use a different proximity volume control board and avoid modifying the original volume control all together. It will be 5 more months till my own tech friend can validate my volume control design.
Have your tech study my un-proven Volume Control.
Happy Holidays
Christopher
Okay, will do...
You posted a request for schematics to BIG BRIAR 91A.
I use to have one but foolishly sold it. Now there's one's up on eBay for 10K !!!
I wonder IF that guy would carefully PHOTOGRAPH the BOARDS- top and bottoms?
They could be reversed engineered??
Q. Have you found the schematics yet?
Most ALL say they don't exist anymore.
It would be a bitch if the 91A broke down. Who could fix them????
[ I'm building a Clara RCA... at least trying.
rely
ROSS
Call???
360-421-7195
As far as I know, the schematics of the BIG BRIAR 91A/B/C have never been published. I haven't fully reverse-engineered it in every detail, just enough to understand the principle of operation which is very different from a "classic" heterodyning theremin. The technical description (below) was naturally extremely helpful. This, in combination with my "normal" Theremin, analog Synth, and general RF experience, is enough for me to be able to service and - if needed - fix or upgrade these beasts for the handful of my French, Swiss, and British clients who own one. But I must say that these instruments are extremely robust and - once fully serviced - I do not see them again before 5 to 8 years.
Here the excerpt from the Series 91 manual:
SPECIFICATIONS
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 (2-1/2 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-nickel-plated straight brass tube, 19 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.
In addition, instruments equipped with a MIDI interface incorporate a dedicated microcomputer for performing the MIDI transmitting, receiving, and processing functions. * (see my note below)
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 257 kHz signal, while the volume antenna circuit is excited with a 450 kHz signal. The effects of the proximity of the player's hands are measured by phase detection circuits that are coupled to the antenna coils. The output of each phase detector circuit is a control voltage that is used to control the sound generating circuitry and produce the desired MIDI messages.
The tone generating circuitry uses contemporary analog synthesizer technology to emulate the waveforms of Prof. Theremin's instruments.
RESPONSE SPEED: Pitch and volume of tone respond essentially instantly (delay time less than two milliseconds) to the motions of the player's hands.
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 an eight-ohm external speaker is included. It is protected by a fuse which is accessible on the power panel.
POWER REQUIREMENTS: 100-120 volts or 200-240 volts (switch selectable), 50-60 Hz AC, 30 watts. Power is applied to the instrument through an international-standard three-conductor power line receptacle.
* Moog had initially planned to bring also a Midi version, the 91M to the market, but this never happened. Instead, the Ethervox was created, which has 2 "voices", one classically heterodyning, and one in the Series 91 technology, and which has Midi functionalities.
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