The PPA headphone amplifier was designed by Team PPA in late 2002 as a community service project. Over the past few years, PPL created a series of pocket headphone amplifiers using opamps and open loop buffers which were the inspiration for Apheared's #42 and the META42.
It's a PPA-Inspired META42 successor. It's about the same size as the META42 board, but the topology is closer to that of the PPA.
An adaptation of the Linkwitz acoustic simulator as a front-end for headphone amplifiers with very high input impedance. This circuit features a continuously adjustable Soundfield control.
This project is a follow-up to the article A DIY Headphone Amplifier With Natural Crossfeed. The author shows a natural crossfeed filter design with a bass emphasis to compensate for low-frequency cancellation effects.
The author details modifications for the HD500 headphones that correct their bright and "phased" sound. The result is an extended frequency response and better dynamic range that make these headphones among the "best headphones on the planet."
A simple acoustic simulator that uses shaded crossfeed to create a more realistic sound image in headphones. It has a "perspective" switch to adjust the level of crossfeed and can feed a headphone amplifier input or drive headphones directly.
Unlike loudspeakers, headphones generally require some equalization to achieve the most balanced sound. This article examines several passive and active equalizer designs that frequently appear in circuit compendiums. All of them are portable, and the active versions can be powered from batteries.
Electrostatic headphone built in the enclosure of an old pair of dynamic headphones. The author gives detailed instructions for constructing the electrostatic transducers and a high voltage amplifier from PA transformers.