Vocal Zapper

Description: All vocal eliminators start with the assumption that the lead vocal in a recording is in the center of the stereo field - which means that it is equal amplitude and phase in both left and right channels. Subtracting one channel from the other removes this highly correlated signal while leaving the uncorrelated signals in the channels unchanged. Since kick drum and bass are often recorded at stereo center the time constant of C3 and R12 is chosen so that these signals are blocked from the non-inverting input so they pass to the final output without being zapped.

In the Vocal Zapper circuit one channel is subtracted from the other by applying them to the inverting and non-inverting inputs of opamp IC1. The Normal/Zap switch allows the vocal elimination function to be disabled by switching the J2 signal from the non-inverting opamp input (Zap) to the summing junction at the inverting input of the amp (Normal). Note that the output signal at J3 and J4 is mono in either Zap or Normal mode.

IC2 is used as a mic preamp to boost the microphone signal level so that it's comparable to the program material and this high level signal is connected to the summing junction at the inverting input of IC1.

The Vocal Zapper circuit is designed to effectively isolate and eliminate lead vocals from a stereo audio signal. The fundamental principle relies on the fact that lead vocals are typically panned centrally in the stereo mix, which means they have equal amplitude and phase in both left and right channels. By utilizing an operational amplifier (op-amp) configuration, the circuit subtracts one audio channel from the other, effectively canceling out the lead vocal while preserving other audio elements that are not centered.

The circuit architecture begins with the application of the left and right audio signals to the inverting and non-inverting inputs of the op-amp IC1. The configuration allows for the differential processing of the signals, where the highly correlated vocal signal is attenuated. Components C3 and R12 play a crucial role in defining the time constant that filters out low-frequency components, such as kick drum and bass, which may also be centered in the mix. This ensures that these elements pass through the circuit unaffected, maintaining the integrity of the overall audio output.

The Normal/Zap switch, located at the input stage, provides operational flexibility. In the 'Zap' position, the circuit performs vocal elimination by routing the audio signals to the op-amp as described. Conversely, in the 'Normal' position, the signal from the non-inverting input is redirected to the summing junction at the inverting input, allowing the user to hear the original audio mix without vocal removal.

Additionally, IC2 serves as a microphone preamplifier, boosting the microphone signal to a level that matches the program material. This is essential for maintaining a balanced output and ensuring that the microphone input can effectively contribute to the audio processing without introducing noise or distortion. The high-level signal from IC2 is also directed to the summing junction of IC1, allowing for seamless integration with the rest of the circuit.

The outputs of the Vocal Zapper, located at J3 and J4, provide a mono signal regardless of the operational mode, ensuring compatibility with various audio systems and setups. This design allows for effective vocal elimination while preserving the overall quality of the audio signal, making it a valuable tool in audio production and live sound environments.All vocal eliminators start with the assumption that the lead vocal in a recording is in the center of the stereo field - which means that it is equal amplitude and phase in both left and right channels. Subtracting one channel from the other removes this highly correlated signal while leaving the uncorrelated signals in the channels unchanged.

Since kick drum and bass are often recorded at stereo center the time constant of C3 and R12 is chosen so that these signals are blocked from the non-inverting input so they pass to the final output without being zapped. In the Vocal Zapper circuit one channel is subtracted from the other by applying them to the inverting and non-inverting inputs of opamp IC1. The Normal/Zap switch allows the vocal elimination function to be disabled by switching the J2 signal from the non-inverting opamp input (Zap) to the summing junction at the inverting input of the amp (Normal).

Note that the output signal at J3 and J4 is mono in either Zap or Normal mode. IC2 is used as a mic preamp to boost the microphone signal level so that it's comparable to the program material and this high level signal is connected to the summing junction at the inverting input of IC1.