The JBL SG-520 E is a stereo control amplifier that was manufactured between 1968 and 1972 in the USA. It features a unique design with a straight-line control configuration and a push-button switch, foregoing traditional rotary knobs. Internally, the circuit design has been improved over time, maintaining the same model number. This preamplifier includes a built-in 1 kHz test tone oscillator and can be paired with relay control components. A notable feature is the Aural Null Balancing System, which allows for stereo volume balance control. The SG-520 E has an output level of 3V and supports a frequency range from 20 Hz to 20 kHz. Input sensitivity is rated at 6 mV for phono inputs and 300 mV for auxiliary inputs. Its total harmonic distortion factor is impressively low at 0.15%. The tone control features adjust high frequencies up to 20 kHz, with a range of +21 to -17 dB, while low frequencies can be adjusted at 20 Hz, also ±17 dB. Additional features include a loudness control and an Oral Balancer. The SG-520 E is available in an aluminum front panel variant, with alternative finishes such as the SG520G with a gold panel and the SE520E with voltage-switching capabilities. Upon release, the original price was approximately 2,540 DM.
