Yamaha disklavier MX-100A, Product Handbook

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MPX70, GT15, GT20, MarkIII
Light-quantity change curves are preset at the factory for each sensor and key, and these values are
written into the sheet. Specifically, after the sensor has been installed the light quantities at open, rest,
and end positions are measured for each key, and used to generate a change curve for that key. The
key-specific curve is then used to determine the appropriate percentages (relative to at-rest light quan-
tity) for points K1 to K4 for that key. By setting percentages separately for each key (unlike the case
with the GT1, where percentages apply in common to all keys), it is possible to correct for manufac-
turing disparities in sensors and keys, providing for more stable operation.
Typical Hammer Sensors and Their Structures
Starting from the MarkII, Hammer Sensors are either 1-beam 2-points or 1-beam 4-points. The 2-points sensor
utilizes a shutter with a single slit, while the 4-points sensor uses a double-slit shutter.
Most models use the 2-points sensor, but the DGPS, PRO, and MarkIII use the 4-points. During silent-
mode operation the hammers cannot reach the strings (owing to the action of the shank stopper). But it
is desirable to detect the hammer movement from as close to the string as possible. The use of the 4-
points sensor makes it possible to shift detection points depending on whether play is acoustic mode or
silent mode.
1-beam 2-points 1-beam 4-points
H1
H2
H1
H3
H2
H4
Acoustic
Silent