A major feature of the AD-2850 is the use of a balanced configuration or the internal circuitry. Separate input stages optimized for MC and MM cartridges respectively bring out the best performance from every cartridge. When using the MM input, high output impedance matching is achieved by means of a low noise FET configuration. By contrast, the MC input needs to handle very low-level signals with low input impedance. This is realized by the use of a differential input circuit with low-noise bi-polar transistors together with a low-impedance NFB loop, resulting in playback with minimal noise. Also, the built-in differential RIAA equalizer circuit with using high-precise components for both feedback side and ground side is designed to provide super accurate RIAA equalization characteristics. The MC input impedance can be switched to 10, 30, 100, or 300 ohms, while the MM input impedance is fixed to 47 k ohms. In addition, the gain can be set to 60 or 70 dB for MC and to 30 or 40 dB for MM. All of these functions are controlled with switches on the front panel of pre-amplifiers. Operation convenience therefore is exactly the same as when using a pre-amplifier with built-in phono equalizer.

The AD-2850 can be used in the models C-2820/C-2810/C-2800/C-2420/C-2410/C-2400/C-290V/C-290. However, the 300 ohm position for the MC impedance can be used only in the models C-2850/C-2820/C-2420, because other models have no corresponding selector position on the front panel. Also, the actual gain will be different from the indication of the AD gain selector knob as follows. MC: 60dB, 70dB, MM: 30dB, 40dB.