Turntable Speed
Monitor - 唱盤速度計
Speed inaccuracy
is one of the most audible corrupters of your turntable¡¦s performance.
A speed
variation of just six percent can alter pitch by a full sharp or flat,
and the
effect is broad-band, changing every frequency reproduced.
Stroboscope has been widely used to measure the speed of
turntables.
A range of products for turntable speed measurement available in the
market are
based either on the idea of stroboscope or different improved versions
of the
stroboscope. Despite of its popularity, the stroboscopes or even those
improved
versions actually fail to provide accurate speed measurement and it
deserves
our attention. To address this shortcoming, I designed and built my own
device,
the Turntable Speed Monitor, for accurate turntable speed measurements.
A microcontroller running at 14.318MHz is used in the
Turntable Speed Monitor. The crystal
oscillator provides a very accurate timing signal so it can perform
almost errorless
measurements of the turntable speed. By using an infrared photo
interrupter (with
a tiny plastic part attached on the edge of the turntable), the
Turntable Speed
Monitor can perform speed measurement without any contact with the
turntable.
It helps to reduce any ¡§side effects¡¨ to the turntable operation. The
speed
measurement can be performed during record playing and the ¡§real¡¨ speed
is
measured.
The Turntable Speed Monitor is operated by four AA
batteries
or a 5V or 6V adaptor. It can measure turntable speed running at 33
1/3, 45 or 78
RPM. The measured speed is displayed in four digits, up to two decimal
points. (For
33 1/3 RPM, the error of 0.01 RPM is just about 0.03% error!) It
provides the most
accurate and easiest operation for speed measurement.
Turntable Speed Monitor Operation Instruction
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