Electrostatic mid-1970's Superex Electronics Corporation out of Yonkers, New York model PEP-74 headphones with it's original energizer console have come into my possession. The owner paid U$68 before tax in 1976 for these including the self-biasing energizer, which is equivalent to U$375 in 2024 dollars. I cleared away exterior and interior deteriorating foam, modified their interiors for diffusion of the 0backwave and put on some recycled flat ear pads. Only then did I plug them into the energizer giving them soft music continuously for several days as the left and right sides came back to life at different stages.
They sound so good for my melodic jazz that I'd been repeatedly listening way past midnight. Satisfied with my modification I fortuitously picked up an old Superex stable alternating current ("AC") bias type of design energizer which makes them sound even better keeping me immersed for hours. (The original box show a rock band and I've read these are also excellent for Rock music.)
[As I've read elsewhere: self biasing designed energizers' transformers have more windings than "AC" transformers which puts comparatively more voltage on the transformers' output coil when the input voltage is otherwise the same for both types of energizers and downstream that comparatively lessens transient response and the linearity of frequency responses. Due to relatively inferior impulse response the musical impact is less and so comparatively we perceive the sound as thinner and more indistinct; the sound stage droops, the bass from self biasing transformers sounds weaker and turning the volume up too much introduces bass distortion. I've read self biasing energizer design introduce a higher input impedance into their output transformers and in contrast "AC" bias energizers get by with lower input impedance into their transformers. This detail of "AC" bias energizes contributes to the better bass, tone and flowing richness of sound obtained from "A.C." energizers in contrast to the different self biasing units' higher input impedance which downstream shows up in restricted frequency bandwidth. Thus the self biasing energizers relatively lose both bass extension and high treble; turning up the volume to compensate for thin sound can cause THD to increase during musical peaks in the upper midrange frequencies at the same time those sound brighter. And the difference between functional design means the self biasing energizer can provoke unpredictability among the assorted harmonic orders while the "AC" bias energizer avoids harmonic randomness.]
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