team theremin1 analog theremin using vacuum tubes and frequency detection via band-pass filters matt...
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Team Theremin 1
Analog Theremin Using Vacuum Tubes and Frequency Detection
via Band-pass Filters
Matt Britt, Ryan Adams, William Findley Jr., Yuri Yelizarov, James Lewis
Georgia Institute of TechnologySchool of Electrical and Computer Engineering
March 4, 2008 and March 6, 2008
Team Theremin 2
Analog Theremin and Frequency Detector
• The Theremin is an electronic musical instrument controlled by interaction with volume and pitch antennae.
• The frequency detector is designed to assist new players in playing on the musical scale.
• The target customers are musicians.• The projected cost of the Theremin is $550.• The projected cost of the frequency detector is
$145.
Team Theremin 3
Theremin: Technical Objectives
• Designed using vacuum tubes in order to suit the preference of musicians.
• Safe to use.
• Dynamic pitch and volume ranges to provide sufficient playability.
• Tuning controls to allow adjustments in player stance.
• Compatible with standard audio equipment.
• Finished case design in a form suitable for a final product.
Team Theremin 4
Theremin: Block Diagram
Team Theremin 5
Theremin: Technical Specifications
• Output of the pitch circuit will cover a 30 Hz to 1 kHz range of sound.
• Volume circuit will produce a control voltage for the voltage-controlled amplifier.
• Power supply circuit will provide two power rails: 6.3 VAC at 2.5 A and 75 VDC at 10 mA.
• The output will use a standard audio equipment line-out, max 1.4 Vrms.
Team Theremin 6
Pitch Control Overview
• RF signals generated by Colpitts oscillators at ~500 kHz
• Mixer is a triode biased in non-linear region• Low-pass filter is a two-pole RC cascade
Team Theremin 7
Pitch Control Circuit
Pitch Reference Oscillator
Pitch Variable Oscillator
Mixer
Low-pass Filter
Team Theremin 8
Pitch Control Performance
• First versions– High harmonic output– Unable to produce tones
below 500 Hz– Smaller effective pitch
range
• Current version– Near-sinusoidal output
from oscillators– Able to produce low
frequencies– Strong RF signal difficult to
isolate
Team Theremin 9
Volume Control Overview
• Uses another RF oscillator at 480 kHz• High-Q band-pass filter using ceramic resonator• Peak detector circuit via level shifter and rectifier• Voltage controlled amplifier in form of a differential
amplifier
Team Theremin 10
Theremin Design Approach
• Research possible circuits
• Hand design using published and simulated I-V curves
• Simulation using phenomenological triode SPICE model– Imperfect– Model better for
“high” plate current Published plate characteristics for 12AU7A twin triode. Circa 1956.
Linear amplifier
Nonlinear mixer
Team Theremin 11
Frequency Detector Overview
• Objective:– Indicate to the user which output is being used by the Theremin.
• Problem:– The Theremin produces a wide range, continuous signal.– With most instruments, a user knows exactly what pitch is
produced.– The Theremin relies on the musician’s ear and muscle memory.
• Solution:– An external system that lights up an LED corresponding to an
output frequency produced by the Theremin.– An LED is provided for each pitch of a chromatic scale.
Team Theremin 12
Frequency Detector Block Diagram
Team Theremin 13
Frequency Detector Building Blocks
• Gain = (Z1 + Z2)/Z1
• Increasing the impedance Z2 or decreasing the impedance Z1 will increase the gain.
• Increasing the impedance Z1 or decreasing the impedance Z2 will decrease the gain.
Team Theremin 14
Frequency Detector Notch Filter Simulation
Team Theremin 15
Frequency Detector: Combining Elements
R1 = 10 kΩ
RL = 1 kΩ
L1 = 3 mH
C1 = 43.6 µF
Op Amp Gain: 1000 V/V
Input Signal: 1 Vrms
Signal Range: 400 Hz – 500 HzNumber of Points: 500
Team Theremin 16
Frequency Detector Simulation
Team Theremin 17
Demonstration Plan
• Measure DC voltage of the antennae, should be less than a few millivolts.
• Demonstrate pitch range, straight antenna.– Keep volume hand steady and change
position of pitch hand.
• Demonstrate volume range, loop antenna.– Keep pitch hand steady and change position
of volume hand.
Team Theremin 18
Problems: RF Propagation
• RF propagation issue:– High power, 5 Vpp, signal coming out of the
oscillators may cause coupling and propagation along power rails.
• Alleviation:– Careful routing of traces and wiring on PCB
and placement of decoupling capacitors.– Reduced signal on DC power rail from 1 V to
10 mV.
Team Theremin 19
Problems: Mixer Design
• Nonlinear design issue:– Nonlinear mixer behavior is difficult to predict.– The practical results differ greatly from
simulation.
• Alleviation:– Trial and error used to get current result.– A curve tracer may be used later.
Team Theremin 20
Project ScheduleTask Owner Status
Evaluation and ordering of tubes
Matt Britt Completed
Building prototype board Ryan Adams Completed
Oscillator design and testing Matt Britt Completed
Antenna design Will Findley Completed
Frequency detector design Yuri Yelizarov In progress
Mixer design Matt Britt In progress
Voltage controlled amplifier design and testing
James Lewis In progress
Power supply design and testing
James Lewis Not started
PCB board design and layout Will Findley Not started
Final construction Ryan Adams Not started
Team Theremin 21
Theremin Cost Analysis
• Projected sales volume of 10,000 over a four year period.
• Three group members working on Theremin portion of project.
• The cost of each Theremin unit is $550.
Description Unit Cost Overall Cost Type
Development Personnel
$36,000 Non-recurring
Development Capital Equipment
$10,000 Non-recurring
Development Overhead 200 %
$92,000 Non-recurring
Total Development Cost $138,000
Parts $200 $2,000,000 Recurring
Production $50 $100,000 Recurring
Market and Sales $100,000 Recurring
Total Recurring Cost $2,200,000
Recurring Cost Overhead, 150% $3,300,000
Adjusted Recurring Cost $5,500,000
Team Theremin 22
Frequency Detector Cost Analysis
• Projected sales volume of 20,000 over a four year period.
• Two group members working on frequency detector portion of project.
• The cost of each frequency detector unit is $145.
Description Unit Cost Overall Cost Type
Development Personnel
$24,000 Non-recurring
Development Capital Equipment
$10,000 Non-recurring
Development Overhead 200 %
$68,000 Non-recurring
Total Development Cost $102,000
Parts $50 $1,000,000 Recurring
Production $30 $60,000 Recurring
Market and Sales $100,000 Recurring
Total Recurring Cost $1,160,000
Recurring Cost Overhead, 150% $1,740,000
Adjusted Recurring Cost $2,900,000
Team Theremin 23
Current Status
• Circuit built on tube “breadboard”.
• Pitch control circuit works up to the low-pass filter.
• Band-pass filter, for volume control circuit, is designed.
• Antennae material is decided on.
Team Theremin 24
Questions?