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First, we decided to use a battery of multiple parallel lm capacitors to provide the bias voltage. Film Capacitors hold
their charge almost indenitely. Given that isolation resistance of the electrostatic headphone is also very, very high, no
current ows to discharge the capacitor bank. Therefore, if we charge the capacitor bank up to the nominal bias one
time, we can simply leave the charged capacitor bank to “oat” at the Bias Voltage.
In order to provide this one time charge we employ a very high frequency switching system (appx. 750kHz). This system
uses a tiny, fully shielded transformer and exotic ultra-fast high voltage rectiers. More crucially, this system shuts down
completely as soon as the correct bias voltage has been established in the capacitor bank.
As some minor discharge happens even through air, we do need to top up the capacitor bank every 30 second or so. This
process usually takes a few millionth of a second (microseconds) as usually one or two switching cycles
suces to replenish the lost charge. Then the switching system is again o completely.
Any noise that this system creates is conned to medium frequency radio bands for the infrequent short durations
during which it is active. For over 99.999% of the time the charging circuit is completely o.
The result is in eect a perfect high voltage battery to provide the bias for the electrostatic headphones. Two13
completely separate and independent bias circuits are employed, one for the 230V “normal” bias and another adjustable,
to cover a wide range of modern electrostatic headphones.
The entire signal switching for the input selection utilises gold-plated silver contact miniature relays lled with an inert
gas. This makes sure the contacts will remain like new for a long time to come.
The loudspeaker connections are switched using sealed silver alloy contact relays for minimum impact on the sound
quality of the loudspeaker path.
The Signal Routing
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