A balanced modulator or mixer is used for modulating components of a chrominance signal onto a subcarrier to generate double-sideband suppressed-carrier amplitude-modulated signals. The video component is applied to a phase splitter which produces two antiphase baseband video signals, which in turn are applied to modulator switches driven in antiphase at the carrier rate for producing the DSB SC signal at a common output terminal. For reducing residual carrier output resulting from unbalance of the video during black level, a sample-and-hold circuit is coupled to each output of the phase splitter and is gated during black level. A differential amplifier compares the sampled signals and reduces the unbalance in a feedback manner to eliminate residual subcarrier during black level.