What is "Active Drive"?

Active Drive

Output stage for microphones developed by DPA.

Balancing the output of a microphone can be done with or without a transformer. The transformer provides a perfect balance. However, the impulse response of the microphone signal can be affected by various high-frequency losses and distortion in the transformer due to magnetic reluctance.

To obtain maximum transparency, the transformer may be avoided, but the output circuitry must be designed to retain the best possible balance throughout the frequency range from very low frequencies close to DC and up in the MHz-range. In the active drive design, a circuitry with zero output impedance is implemented. The absolute impedance of the output (pin 2 and 3) is then determined exclusively by the matched output resistors and the resistors by which the phantom power is provided.

It is a straight forward circuitry that provides the headroom needed for very dynamic signals.