Which device is primarily responsible for amplifying audio signals to be modulated?

The speech amplifier is primarily responsible for amplifying audio signals before they are modulated. In audio transmission systems, the initial audio signal—such as speech—may be weak and needs to be enhanced to ensure clarity and reach when transmitted. The speech amplifier boosts these audio signals, enhancing their intensity without significantly altering the original quality.

Once the audio has been amplified, it can then be fed into a modulator, where the amplified audio signal is combined with a carrier wave to create a modulated signal suitable for transmission over various media. By focusing on the amplification of the audio signals prior to modulation, the speech amplifier plays a crucial role in ensuring that the transmitted signal retains intelligibility and fidelity, which are essential for effective communication.

Other devices, like mixers and modulators, are vital in their respective stages of audio processing for adjusting levels and combining signals, but they do not serve the primary function of amplification. Therefore, the speech amplifier stands out as the correct instrument in this context.