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There are several ways in which lower tones can be added to the lower manual of a spinet.

The main problem to be surmounted is that the ToneGenerator in a spinet is missing some of the needed tones. To extend the range of the lower manual down one octave, one needs to add tones 6 through 17. The pedal tonewheels (1 through 12 (or 13, depending on model) are not readily useable for the lower manual. (The pedal tonewheels are "complex shaped" to produce tones rich in higher harmonics --- furthermore their pickups are wired in series, to support pedal sustain.) Tones 13 (or 14) through 17 are simply not present in the ToneGenerator.

(Finding key contacts to switch the added tones is not such a problem. One can simply rewire the inputs to the manual to transpose the whole thing down one octave, or one can dig deeper and rewire the manual in various ways. See also AddATenthSetOfContacts.)

Three approaches have been reported:

  1. FrederickSomerville has wired an Octavider into the output of the lower manual. This allows one to play bass on the LM (but only monophonically.) See http://www1.tripnet.se/~flm/hammond/diff.htm#octavider for Frederick's notes.
  2. GeoffWilliamson used a bank of twelve home-built dividers to generate the missing twelve tones, and rewired the inputs to the lower manual to transpose it down an octave. See http://www.sympac.com.au/%7eretrojet/LHBass.htm for his notes. Geoff now has his circuit on printed circuit board and has kits available for spinet owners who want to play left hand bass.
  3. NigelPiper has successfully wired a Trek II String Bass Unit, normally designed to be played from the pedals, to the bottom one and half octaves of the lower manual. By nulling all but one row of contacts (used for the String Bass) on the left side, and transposing the frequencys up on the right side, the lower manual is split between bass and comping tones (which are now in the right register).

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