This circuit is designed to boost a low audio signal when connected to a power amplifier. It provides a fixed gain of 10 times (20 dB) and includes a front 3.5 mm interface for headphones. Key benefits Improves listening level for devices with low output by supplying a dedicated gain stage before the power amplifier Simple integration between a source device and a power amplifier without modifying the source Front 3.5 mm headphone jack allows direct headphone connection for monitoring or casual listening Specifications Amplifier chip: NE5532 dual opamp Gain: 10x (20 dB) Power supply: DC 919 V Input/output: front 3.5 mm headphone interface Use scenarios Scenario 1: Pair a portable music player with a power amplifier to achieve higher playback volume for headphones or speakers Scenario 2: Insert between a small audio source and a power amplifier in a home or studio setup to obtain adequate loudness without altering the source device Scenario 3: Include in a DIY audio project as a fixed gain preamplifier for headphone monitoring or signal conditioning before amplification