Before revision: Whereas most portable electronics run off of a 1.8, 2.5 or 3.3 Vpp supply, many headphone amplifiers run off of 10, 18 or 24 Vpp volt supplies, allowing 5-20 dB higher volume.
After revision: Whereas most portable electronics are powered by a 1.8, 2.5 or 3.3 Vpp supply, many headphone amplifiers use 10, 18 or 24 Vpp supplies, allowing 5-20 dB higher volume.