Sample & Hold Modification
Provides Note Bender
A modification of the Sample and Hold circuit in the Keyboard Controller of my synthesizer provides a note bender. This effect is used extensively by Jan Hammer (with Jeff Beck), Patrick Moraz (Yes) and Roger Powell (Utopia). It is used the same way as a guitarist bends a note.
The problem with using the pitch control as a bender is that once you have bent a note you must again "find" the correctly tuned location. Using the fine tuning modification, Polyphony 3/76, does not completely solve the problem. It can be used to bend notes down in pitch but not up (zero resistance is the least you can go). This means that you would have to compensate for a "full on" position on the fine tune control by raising the coarse adjust. This greatly diminishes the range of the keyboard.
To get around this I replaced the 1800 ohm resistor that is in parallel with the pitch control with a 1000 ohm slide pot in series with an 820 ohm resistor. Together they are in parallel with the pot. When the pot is "full on" there is around 1800 ohm (close enough). However, as the pot is moved toward zero resistance the series combination approaches 820 ohms thus allowing more current. I've found that when using the keyboard on the middle pitch range (16') that it allows a bend of about 2 half steps which is perfect for most applications. It also is fun to use.
Raising the pitch control to the next octave diminishes the range of the bender since the pitch control itself is approaching zero resistance. But on the 16' range it is a great effect.
A rotary pot would work but I used a slide pot since it's easier to "feel the bend" and return to normal after the bend. One disadvantage to a slide pot, though, is cutting the panel.
Feature by Barry Nesmith
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