Accuphase DG-28 (1997)

Name: Accuphase DG-28
Brand: Accuphase

Digital voicing equalizer with 64-band correction and automatic room calibration

Overview

The Accuphase DG-28 is a stereo digital equalizer released in May 1997 as the successor to the DG-18. Accuphase Laboratory, Inc. built it to work entirely in the digital domain, with dual DSPs per channel doing 48-bit internal processing. It comes with a calibrated AM-28 measurement microphone and analyzes the room automatically using a warble tone sweep. It corrects speaker and room response anomalies and stores up to four user presets (A-D) in non-volatile memory. It works as a stand-alone processor. Optional digital I/O boards let it integrate with compatible Accuphase gear like the DC-300 preamplifier and DP-75V CD player.

Specifications

Format	Digital 1/6 octave 64-band (switchable to 1/3 octave 32-band)
Frequency Range	16 Hz to 22.4 kHz (ISO standard, ±0 dB at 48 kHz sampling)
DSP Configuration	Two DSPs per channel (four total), 48-bit internal processing
Dimensions & Weight	475 x 150 x 393 mm, 13 kg
Power	100 VAC, 50/60 Hz, 12W consumption
Memory	Four user profiles (A–D), retains settings when powered off
Inputs/Outputs	Optical & coaxial digital I/O (EIAJ CP-1201), 16–24-bit, 32/44.1/48 kHz auto-detect
Remote Control	RC-21 infrared, powered by two AA batteries
Included Accessories	AM-28 microphone, 5m mic cable, stand, two 75Ω coaxial cables, power cord

Design

The DG-28 uses Accuphase's proprietary filter algorithm, with parallel-connected filter engines on each channel to keep calculation errors and noise down. Each channel has 64 filter cells in a "filter engine," and unused cells are deactivated so they don't degrade the signal. Clock stability comes from an ultra jitter-free PLL circuit built on a crystal oscillator and preamble detection. The 320x240 dot LCD sits under a screw-mounted front cover, which also hides the microphone jack and the less-used controls. Tone generation and analysis are DSP-based, so automatic correction of both channels takes about 5.5 minutes. Up to four optional analog I/O boards can go in the rear slots.

Context

Accuphase positioned the DG-28 as a high-end answer to room acoustics. It competed with units like the TacT RCS 2.0 and Behringer Ultracurve Pro DSP 8024. It was marketed as a tool for listening room anomalies that passive methods leave alone. Pair it with the DC-300 digital preamplifier and the signal stays fully digital from source to output. It arrived when digital equalization was gaining credibility among audiophiles for improving spectral balance, imaging, and soundstage stability without adding audible artifacts.

Market

The DG-28 is discontinued and sold only on the used market. Typical listings run from €2,200 to PLN 7,400 (~$2,000-$3,500), with rare outliers as low as €10. Common problems are front panel display failures and a lost or damaged proprietary AM-28 microphone. Service is difficult because the DSP circuitry is complex and legacy components are hard to source. Optional accessories include the AO-B1 analog output board and the AO2-U1 D/A converter module.