7-band equalizer with a +/- 12 dB control range. Equalization bands: 60 Hz, 150 Hz, 400 Hz, 1 kHz, 3 kHz, 6.5 kHz, 15 kHz. Configured with TI or ST TL074 original op-amp arrangement. Core parameters: 7-band sound equalizer preamp; RC4580 classic op-amp provides a 5x gain (14 dB). Input impedance 20 kΩ; output impedance 600 Ω. Headphone compatibility: headphone amplifier section uses NE5532; built from a headphone driver circuit of type 47. Easy to drive; compatible with all types of headphones; adjustable high and low gains. 3.5 mm interface: 3.5 mm input supports 4-pole plugs; the output can be connected to a headset microphone for normal voice calls on mobile phones; an additional terminal with a group interface is available. Use scenarios: - Tailor the sound of portable players or laptops with precise 7-band adjustments for critical listening. - Use with headphones and a headset mic for clear mobile calls, with adjustable gain to suit different devices. - On-the-go audio testing and monitoring with various headphone types, enabling quick spectrum and level checks.