Electronic musical instrument with variable impedance playboard providing portamento

Claim 1

An electronic musical instrument comprising: a musical scale keyboard including keys for musical performance; and a continuously variable frequency oscillator; said continuously variable frequency oscillator including: an amplifier having an input and an output; a portamento playboard for controlling said oscillator over plurality of octaves; said portamento playboard being arranged parallel and adjacent to said keyboard, said portamento playboard including a positionally actuatable variable impedance element mounted therein and extending therewith; said positionally actuatable variable impedance element having a first end and a second end; said positionally actuatable variable impedance element having a plurality of taps disposed at predetermined positions thereon; a plurality of frequency responsive networks each connected to one of said plurality of taps to form a frequency determining network having first and second terminals; said first terminal connected to said input of said amplifier and said second terminal connected to said output of said amplifier thereby forming a feedback loop around said amplifier responsive to the position of said positionally actuatable variable impedance element actuated for providing a frequency responsive impedance value related thereto ; said variable impedance element normally exhibiting an infinitely large impedance value to render said oscillator nonoperative and, when actuated, said frequency responsive impedance value representing the position actuated to render said oscillator operative to oscillate a frequency determined by said frequency determining network; and said portamento playboard being located with respect to said keyboard to provide frequencies from said oscillator when actuated at particular positions corresponding to notes or keys on said keyboard adjacent to said particular position.