The Black Pearl is a project whose intention was to create the most versatile headphone amplifier with a reasonable price. One of its features is keeping stable electrical parameters within a broad range of DC power supply voltage which enables it to be used with an external battery instead of the PSU. This allows to further improve sound quality making it independent from the mains voltage stability and interference coming from the grid.
The Black Pearl might also work as an active line preamplifier if such option is chosen, with another pair of RCA sockets on the rear panel and larger enclosure.
The colors of the enclosures for both the amplifier and the external battery can be chosen between metallic black, blue, red and silver with black frames. These are Hammond 1455K1601BK or 1455K1601 models for the basic amplifier confugration and the external battery. The amplifer with the line out option uses the 1455N1601 series enclosure. 
Technical data:
- supply voltage: 3-26V DC
- input impedance: 10kΩ
- maximum output voltage: 8.7V
- output impedance for headphones: 0.61Ω
- output power: 2.36W/32Ω, 0.25W/300Ω, 0.13W/600Ω
- channel separation at 1kHz: 52dB on 16Ω headphones, 80dB without load
- gain: 13dB
- frequency response on 16Ω headphones: 5Hz – 2MHz
- up to 43 hours working time from battery
Premium quality potentiometer - 50€ 
Black Pearl headphone amplifier - 390€
Black Pearl headphone amplifier with line out - 430€
230V AC/24V DC regulated PSU - 20€ 
230V AC/25.2V DC regulated PSU - 30€
External battery 2600mAh – 150€
Automatic battery charger 100~240V 50/60Hz – 50€
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