Legacy Products

HD-231 – Dual 31 band Graphic Equalizer


The HD-231 is dual, 31 band, 1/3 octave graphic equalizer ideal for live sound systems, PA systems, permanent or fixed Installations, church systems, nightclub systems, practice PA systems, DJ sound systems, as well as home and project studios. With so many useful features and rugged construction, the HD-231 EQ will prove its value with every gig and live performance.

Key Features


Controls Overall Gain Range: / Off to +6dB (Unbal. out) Sliders Centered / Off to +12dB (Bal. out) Sliders centered
Filter Type Constant Q, 3% Center Frequency
Input/Output Connections INPUTS

  • Input Type: Active Balanced/Unbalanced
  • Connectors: 3-Pin XLR, 1/4″ TRS (Bal.), Euroblock
  • Impedance: 24k Ω (Balanced); 12k Ω (Unbal.)
  • Maximum: Level +22dBm (Level Control at Center)


  • Type: Active Balanced / Unbalanced
  • Connectors: 3-Pin XLR, 1/4″ TRS (Balanced), Euroblock
  • Impedance: Typical
  • Max Level: +22dBm (Bal., 600 Ω load) +16dBm (Unbal., 2k Ω load)
  • RFI filters: Yes
  • Bypass Switches: Yes, Passive
  • Overload: LED Threshold 6 dB below clipping, (all filters set to flat)
  • High Pass Filter: 10-250Hz, 12dB/Oct
  • Low Pass Filter: 3k-40kHz, 12dB/Oct
  • Frequency Response: 20-20kHz, +/-0.5dB
  • THD + Noise: less than 0.01% (20Hz-20KHz, 0dBu)
  • IM Distortion (SMPTE): 0.005%
  • S/N Ratio: >98dB, Ref: 0dBu, (Bal.) 20Hz – 20KHz, unweighted.
  • Headroom: +22dB, Ref, 0dBu, (Bal.) (+/-6dB and +/-12dB range)
  • Dynamic Range: >117dB, (Bal.)
  • Channel Separation: >60dB
  • Common Mode Rejection: 50dB typical
Power 95-125VAC, 50/60Hz, 190-250VAC, 50/60 Hz
Power Requirements Input AC Power: 14 W, typical
Range +/-6dB or +/-12dB (Selectable)
Size 3.5″H x 19″W x 7.0″D
Slider Travel 20mm (Positive Center Detent)
Weight 12 Ibs (5.4 kg)