The V301H "California" Continental - Drawbar and Preamp Circuits

When you pull out the four white "voicing" drawbars, and play the lowest,
or "C1" key in the illustration above, the resultant sound will be composed
of these seven distinct pitched tones. This same seven tone relationship will
be present on every key of the Continental Organ, and explains how the Vox
Continental developed a more Hammond like tone than other 1960's organs.

The V301H preamp circuit
The drawbars on the Continental organ are used for voicing and tone control and are based on the operation of a pipe organ.

The concept of drawbars for voicing control was originally developed by Hammond Organ in the 1940s. Hammond organs used 9 drawbars that controlled the volume of nine different electronically simulated organ pipe lengths. From left to right, these drawbars were connected to tone generators inside the organ that operated the simulated pipe lengths of 16', 5 1/3', 8', 4', 2 2/3', 2',1 3/5', 1 1/3' and 1'

The Vox Continental drawbar system borrowed heavily from Hammond. On the Continental, the left four drawbars are labeled 16', 8', 4' and IV. As on a Hammond organ, these voicing drawbars act as volume controls for the electronically simulated pipe organ lengths they control. The Vox Continental drawbars are connected to the output of the serial dividers on the tone generator cards through the key contacts.

The sixth divider on the tone generator cards produce the lowest tones on the organ (click here for an explanation of the divider operation on the V301H tone generator cards) . The output of the sixth, ot lowest divider on the tone generator card is roughly equivalent to the tone produced by a 16' pipe on a traditional pipe organ. In the lowest octave of the organ, the 16' drawbar is connected to the output of the sixth divider, adjusting its volume. The drawbar may be pulled out to make the tone louder and pushed in to make the tone softer. Again, in the lowest octave, the fifth divider on the tone generator card feeds the 8' drawbar, making a tone equivalent to an 8' pipe on a pipe organ and produces a tone one octave higher than the sixth divider. The same applies to the fourth divider and the 4' drawbar, which produces a tone two octaves higher than the sixth divider.

In the second octave, the 16' drawbar is connected to the fifth divider on the tone generator card. In the third octave, the 16' drawbar is connected to the fourth divider on the tone generator card. In the highest octave, the 16' drawbar will be connected to the third divider of the tone generator card. The similar scheme would apply to the connection of the 8' and 4' drawbars to the tone generator cards.

The drawbar labeled "IV" is called "the fourth rank." The fourth rank is a combination of four tones, again based on the length of the pipes on a pipe organ that would produce these tones. The tones are based on the 2 2/3' , 2', 1 3/5', and 1' pipes. These are considered to be "overtones," and make the tone of the Continental more complex when compared to the Vox Jaguar organ, which does not offer this tonal option. The choice of these four overtones (2 2/3' , 2', 1 3/5', and 1') for the Continental was obviously influenced by the circuits of a Hammond organ, which offered these same four semitones on four individual drawbars.

The two red drawbars adjust the tone of the organ. The left or "~" drawbar offers flute voicing. The symbol on this drawbar, "~" represents a sine wave, the visual representation of a flute tone on an oscilloscope. The right, or "M" drawbar offers the reed voicing, a much brighter tone. The "M" symbol on the drawbar is the visual representation of a reed tone on an oscilloscope. These tone drawbars may be used individually or in combination with each other. Like the white drawbars, these also act as a volume control. When pushed all the way in, the organ will make no sound, regardless of the position of the white drawbars.
Under the orange lid of the organ, directly behind the drawbars, is the two stage preamplifier that prepares the output of the organ for an external amplifier. A master level control allows the total output of the organ to be adjusted to avoid input overload distortion.

You might wish to purchase the recent North Coast Music remastering of the Vox V301H schematic to help you repair the drawbar or preamp circuits. Parts values for all capacitors, resistors, and diodes are included in this schematic. Click here to purchase this from North Coast Music.



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Photos and editorial content courtesy Gary Hahlbeck, North Coast Music

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