Audio Technica AT-706 (1975–?)
A pair of electret condenser headphones from 1975 that still work, with some faint electrostatic sound left in aging foam and old circuits.
Overview
The Audio Technica AT-706 isn't a name like the SL-1200 or the AKG K240. It's a quiet footnote from the early days of high-fidelity personal audio, when electrostatic and electret designs were still being tried out. It was sold as an electret condenser headphone. It needed external power to energize its passive electret elements, but no bias supply, according to DIYAudio reports. That made it simpler than a true electrostatic and more exotic than the moving-coil designs flooding the market. Owners report these were never plug-and-play. They needed a converter box, fed directly from the speaker terminals of a full-sized amplifier. The box, sometimes called an energizer, handled impedance matching and signal conversion, stepping the amp's output down to a level the headphones could use. It also carried a high/low sensitivity switch, a stereo/mono toggle, and clamp-style terminals for the amplifier's speaker outputs. So it was a system, not just a headphone.
Some units have survived decades of storage, disuse, and foam degradation. A Facebook user noted their pair "still working 100%, and that sounds fantastic!" That opinion isn't universal. Another Reddit contributor was less impressed, calling the sound "not the best by any," which suggests performance varied widely with condition and setup. These were not casual listening tools. They were part of a niche ecosystem, likely aimed at audiophiles and broadcast engineers who valued extended frequency response and low mass drivers, even at the cost of complexity. They still come up in obscure forum threads and Facebook groups decades later.
Specifications
| Manufacturer | Audio-Technica |
| Model | AT-706 |
| Type | Electret condenser headphones |
| Production years | 1975–[VERIFY: end year not confirmed] |
| Frequency Response | reportedly 5 Hz – 27 kHz |
| Power requirements | Requires external converter box connected to amplifier speaker terminals |
| Features | Stereo/mono switch, high/low sensitivity switch, clamp speaker terminals on converter |
Key Features
Electret Condenser Drivers (No Bias Supply Required)
Traditional electrostatic headphones require a high-voltage bias. The AT-706 uses electret technology instead: permanently charged diaphragms that eliminate the need for an external bias voltage. According to DIYAudio contributors, this simplified the energizer circuitry and reduced the risk of electrical failure. The driver size and construction materials aren't documented, but the electret approach suggests lightweight diaphragms with fast transient response, a trait some owners associate with the "fantastic" sound they still hear today. Long-term reliability is questionable, though. Electret materials can degrade over decades, potentially leading to loss of charge and diminished output.
External Converter Box with Speaker-Level Input
The AT-706 doesn't plug into a headphone jack. It connects through a dedicated converter box that clamps onto the speaker terminals of a power amplifier. The box acts as both impedance matcher and signal attenuator, stepping the amplifier's output down to a safe level for the sensitive electret elements. Clamp-style terminals were common in the 1970s on test and broadcast gear, which hints at professional or semi-professional use. The box also has a high/low sensitivity switch, so the headphones can be matched to different amplifier outputs, and a stereo/mono toggle, which may have been useful for monitoring broadcast feeds or troubleshooting stereo imaging.
Stereo/Mono Switch
The stereo/mono switch sits on the converter box and collapses the stereo image into a single channel. A Facebook group dedicated to vintage headphone reviews noted this feature, and it suggests the AT-706 was designed with monitoring in mind, perhaps for broadcast engineers checking signal presence or technicians aligning tape machines. In consumer use, it might have helped identify phase issues or simply provided a different listening perspective. Its utility in modern setups is limited.
Historical Context
Manufactured starting in 1975, the AT-706 appeared during a period of rapid experimentation in headphone design. Electrostatic and electret technologies were gaining attention for their potential to deliver extended high-frequency response and minimal distortion. The AT-706 was part of Audio-Technica's AT-700 series, a line that explored high-end transducer technologies before the company shifted focus toward more accessible moving-coil models. It wasn't a flagship, but it represented Audio-Technica's early commitment to pushing the boundaries of personal audio, even in niche formats.
Collectibility & Value
Original pricing in 1975 was reportedly $140, a significant sum at the time, equivalent to a mid-tier receiver. Today the market value is negligible for non-working units, though a complete set with a functioning converter box sold on eBay for $17.76, according to a Facebook post. That price reflects the obscurity of the model and the high failure rate common in vintage electret systems. The most frequently reported issue is loss of volume, likely due to degraded diaphragm charge, failing internal cabling, or deteriorated foam seals. Spare parts are not documented, and repair expertise is scarce. Collectors interested in the AT-706 are typically driven by curiosity or a desire to complete an Audio-Technica lineage, rather than sonic performance.
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