Dc keyed synthesis organ employing an integrated circuit

Claim 1

A keying system for simultaneously keying the desired group of harmonics for a note of a synthesis-type electric organ having a multiplicity of square-wave tone signals, said signals providing fundamentals of the frequencies of the harmonics to be keyed, said keying system to be used with other like systems for other notes of the organ, comprising a keying block, said block comprising a substrate having a plurality of substantially identical sections thereon, one section for each of the harmonics to be keyed, each of said sections having a first and a second field effect transistor formed thereon, all of said transistors having an input, a gate and an output, a direct current supply connected to the input of the first of said transistors of each section, means for establishing the voltage level of said direct current supply at any of several levels individually for each section, circuit means connecting the output of the first transistor of each section to the input of the second of said transistors of the same section, a group of sine filters connected individually to the outputs of said second of said transistors for summing and filtering the signals from the last said outputs to remove all but the fundamentals from the last said signals, a common output circuit connected to receive the signals from said filters, circuit means connecting the squarewave signals individually to the gates of one of the transistors of each sectiOn, and means including a source of keying potential and playing key actuated contacts connected for applying said keying potential to the gates of the other transistors of the block when said playing key contacts are actuated.