Some crossfeed acoustic simulators suffer from frequency-response anomalies (called Comb-filter effects) because they use a fixed, frequency-independent delay in the crossfeed signal. The author has developed a crossfeed filter/headphone amplifier with frequency-dependent delay that eliminates the Comb-filter effect.
http://headwize.com/projects/showfile.php?file=meier_prj.htm
Both the preamp and power amp are fully regulated and feature opamps that are biased to operate in semi-class A mode. The power amplifier can output 32W per channel into a 4 ohm load or can be converted into a mono amp with 4x the output power. It uses 46 opamps per channel and does not require any heatsinking!
http://headwize.com/projects/showfile.php?file=meier3_prj.htm
The principles of electrostatic headphone design and a study of the DIY projects by J.P. Wilson, Philip Harvey and Neil Pollock from a series of Wireless World articles published between 1968 and 1979.
http://headwize.com/projects/showfile.php?file=cmoy3_prj.htm
This design uses two opamp gain stages per channel for superior input buffering and a discrete bipolar output stage with thermal tracking current mirrors. The amplifier's overall gain can be adjusted to match the efficiency and impedance characteristic of any headphone.
http://headwize.com/projects/showfile.php?file=simpson_prj.htm
This tube amplifier with sonic controls has a paralleled White cathode follower output stage for driving low impedance headphones. The sonic controls consist of a Fender tone stack (bass, mid and treble), and ambience and blend controls.
http://headwize.com/projects/showfile.php?file=cavalli_prj.htm
With a fast Motorola buffer as its only active circuitry, this design specifies the highest quality parts and careful construction to avoid signal coloration. The author includes instructions for substituting other buffer ICs.
http://headwize.com/projects/showfile.php?file=pawliw1_prj.htm
Muzzle the din and relax to the sound of silence with headphones that combat the uproar with "anti-noise." The author includes modifications for a binaural microphone headset, an audio probe and a parabolic microphone.
http://headwize.com/projects/showfile.php?file=noise_prj.htm
A DC-coupled headphone amplifier based on the Analog Devices AD844 opamp. This design employs a temperature-sensitive biasing system on the bipolar output stage to prevent thermal runaway.
http://headwize.com/projects/showfile.php?file=jorgen1_prj.htm