Two-IC electric organ LM324
Electronic
74HC00

This Is an electronic organ which uses two ICs, the Operational Amplifier IC and the NAND gate IC.

The organ sound is produced by U2. This works as a voltage controlled oscillator made up of an integrating circuit and a Schmitt circuit.

You can change the frequency of the oscillator by varying the input voltage. That's why it is called "voltage controlled oscillator."

The voltage for producing the sound at different pitches is generated by U1 (Operational Amplifier). U1 produces a voltage corresponding to the pitch selected by S1 to S8. This voltage is applied to the oscillator.

So, you see it's meaningless to turn two or more switches ON at a time. When you finish wiring up the circuit, switch power ON and press S1 to S2, S3 ... This organ can play over a full octave. Turn control volume to adjust musical scale.