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President's Message
December 2003

1.  A circuit note "A Linear Voltage Amplifier" should be of interest to those who eschew negative feedback. The author considers a grounded emitter bipolar transistor amplifier which has inherently high distortion due to the non-linearity of the base-emitter diode. By making the collector load a string of diodes (instead of a resistor) the distortion is canceled. He shows for a 10 mV input signal the distortion is reduced from 1% to .0056%. However the signal level is low, and the gain is only equal to the number of diodes, so it has limited application. Perhaps a low noise head amp for MC cartridges. (He used a SPICE simulation, not actually measurements). Electronics World Jl03

2.  Audio advances in TV transmission are surveyed over the last 20 years in the 17SE03 TV Technology. One area that has gotten worse is audio-to-video synchronization, which "has become a gigantic mess." Every level of video processing introduces delay, so the sound comes out early (which is psycho acoustically unnatural) unless it is delayed too. Tektronix has developed a system called the AVDC100 that allows lip-sync correction via a video watermarking. (I was watching This Old House on PBS Boston and sledgehammer blows were sounding .3 seconds before the visual strike. Steve Owades suggested that this can be a result of the user's system connections: if he is routing the sound directly to the hifi, while the image is being line-doubled in the television (which causes delay), then the sound can arrive early).

3.  "Loud not Fast Wins These Races" leads an article on a dB Drag Racing event in Ohio. The loudest sound wins, but no one can hear it. It has corporate sponsors and championship circuits, top competitors put as much as half a million dollars into their cars, and it can be found from Finland to Bangladesh. This season the average measurement was 142.1 decibels, which is well above the 125 decibels emitted by a commercial jet taking off at full throttle. The international record is 171.5 decibels. And no one stays inside; that would be suicidal. A Voyager being "raced" (seats ripped out to make room for 32 batteries and 16 amplifiers for 44,000 watts) was reinforced to keep the sound from leaking out. In place of windows it had inch-thick sheets of Plexiglas (soon to upgrade to 3") and the door panels had been replaced by plywood covered with duct tape (some contestants fill their doors with concrete). The contestants and crew sat on the roof and windshield to keep the sound from escaping. There are three classes of competition: everyday cars that can be driven on the street; super street, in which everything has been removed and replaced with equipment; and extreme class for the real pros. (NYT 5SE03)

David Hadaway

President, Boston Audio Society



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updated 11/11/04