This FV1 Equal Loudness Volume Controller box boosts the high and low frequencies at low volume levels, so that the loudness ratios of the low, mid, and high sections remain the same as at low, mid, and high volume levels. It doesn't need power supply.
Cautions:
(1) Signal attenuation and gain balance
FV1 passive equal loudness circuit usually realizes frequency compensation through the RC network (resistor-capacitor combination), which may cause slight attenuation to the original signal.
Solution: Increase the amplifier output volume appropriately, but please avoid amplifier overload or distortion.
(2) Impedance matching
Please ensure impedance matching between the controller, amplifier, and speakers. And adjust compensation strength based on volume level manually.
This FV1 box needs to be matched to the impedance of your front-end and rear-end equipment (amplifiers, speakers), otherwise, it may result in:
Reduced signal transmission efficiency: high-frequency loss, dynamic compression
Overheating or damage to the device (especially with extreme impedance mismatches
(3) Audio source quality requirements
The FV1 Loudness Volume Controller box will amplify the source defects (for example recording background noise or compression distortion).
Suggestion: high-bitrate lossless audio sources (such as FLAC, WAV), and avoid low-quality MP3 files. Avoid signal chain interference by using shielded cables.