D-70 is a 30-voice polyphonic synthesizer developed to be a stronger competitor on the market where Korg M1 became a hit. It was devised to be a successor of D-50/550 but actually represents an upgraded U-20 with which it has more in common. The circuitry is even called U-50 inside. The instrument is based on digital ROM samples the idea of which is borrowed from U series. The low pass resonant TVF and TVA are taken from D-50. There are reverb, chorus and flanger onboard and a percussion set integrated.

PCM card slots are featured with a RAM slot allowing to read U series PCM cards. The instrument comprises a selection of bass and lead sounds, as well as some amazing patches such as “Ghosties", "Prologue" and "SpaceDream”. The filter are claimed to be enhanced and are more powerful comparing to the one in D-50 while the overall sound quality was improved and is more convincing than in U220 romplers.

The unit is also a decent proper master keyboard. It has 76 velocity sensitive keys with aftertouch, faders sending MIDI messages, keyboard split option, a large LCD, a pitch bender. Faders are assignable to such parameters as Level, Pan, Tuning, Cutoff, Resonance, Attack, and Release. The control panel allows for tweaking many features in real time including filter sweeps and levels of tones. Memory stores up to 128 patches, 128 tones, 10 user and 64 performances.