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All-Triode Direct-Drive Amps for Electrostatic and Electret Headphones

All-Triode Direct-Drive Amps for Electrostatic and Electret Headphones

Electrostatic headphones, like electrostatic speakers, work on a push-pull arrangement. When one of the stators is going up in voltage, the other stator must decrease in voltage so that the diaphragm can move due to the static charge.
These two direct-drive electrostatic tube amplifier designs will drive any existing electrostatic headphones without step-up transformers. The first is AC-coupled. The second is fully DC-coupled from input to output. These amps can also drive electret headphones – which are just permanently biased electrostatics – as long as the voltage swings are not too high.

I have built a total of 4 of the first amp, and one of the second. These are not beginner projects by any means. Since I have access to a chemistry electronics shop, I used lots of expensive and wonderful parts. The coupling caps I used are .22uF mica caps (probably 30+ years old) from military surplus. Due to the Apex op-amp DC regulators, the second design is a whole bunch more money. Both amps sound better than the Stax SRM-T1S unit, and virtually the same as the Stax Omega (if you could find one). And it definitely sounds better than the Sennheiser Orpheus

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