The Langevin EQ-252-A provided equalisation at seven fixed centre frequencies: 50 Hz, 130 Hz, 320 Hz, 800 Hz, 2 kHz, 5 kHz and 12.5 kHz. Each band had its own sliding lever, allowing the operator to adjust individual areas of the audio spectrum and see the relative control settings across the front panel. Each control offered 8 dB of boost and 8 dB of attenuation, with adjustment in discrete 1 dB steps.
Designed for use during programme material, the controls employed gold-plated switching contacts to provide quiet adjustment. The seven sliders gave direct access to the frequency bands without requiring a separate frequency-selection control. The standard unit was supplied with red control knobs and a black, satin-finished anodised aluminium panel.
The Langevin EQ-252-A used an entirely passive bridged-T circuit. It required only input and output connections, with no separate power supply or internal valve amplification. This arrangement introduced a specified insertion loss of 16 dB. With all controls at zero, the equaliser provided a flat response and presented a resistive network between input and output, retaining that overall signal loss.
Its seven filter sections were designed to overlap. When all levers were aligned at the same boost or attenuation setting, their combined responses produced a flat output across the overlapping bands. This behaviour was part of the relationship between the standard frequency selections and the filter curves. It allowed the controls to work together as an integrated equalisation system, rather than simply as seven unrelated filters.
Special frequency selections were also available to order. These did not necessarily preserve the same flat combined response between adjacent bands, because the standard frequencies had been selected specifically to achieve that overlap. The behaviour of a customised unit therefore depended on its fitted filter frequencies.
Internally, the Langevin EQ-252-A used seven plug-in printed-circuit filter assemblies with miniaturised components and gold-plated etched circuitry. Sealed toroidal coils formed part of the passive networks. The specified equalisation accuracy was ±0.5 dB, and the operating level extended from −70 dBm to +24 dBm.
The equaliser was designed for 600 Ω input and output connections. For installations requiring lower impedances, Langevin specified external TF-602-C line-to-line matching transformers at the input and output. Maintaining the equaliser’s internal 600 Ω design also supported its compact construction: reducing the working impedance would have required larger equaliser components.
The panel-mounted assembly measured approximately 88.9mm high, 266.7mm wide and 146.1mm deep overall. Connections used solder-type turret terminals, and the unit was supplied with mounting hardware and instructions. Its combination of stepped controls, replaceable filter assemblies and passive circuitry provided a defined method of adjusting programme balance across seven selected frequency bands.
Features
- Seven fixed equalisation bands covering 50 Hz, 130 Hz, 320 Hz, 800 Hz, 2 kHz, 5 kHz and 12.5 kHz.
- Individual sliding controls providing up to 8 dB of boost or attenuation per band.
- Stepped adjustment in 1 dB increments.
- Gold-plated switching contacts designed for quiet adjustment during programme material.
- Passive bridged-T circuitry requiring no valves or power supply.
- Seven plug-in printed-circuit filter assemblies.
- Sealed toroidal coils.
- Overlapping standard filter responses designed to produce a flat combined output when all levers share the same setting.
- Special filter frequencies available to order.
- Black satin-finished anodised aluminium panel with red control knobs.