I want to offer you one version of such a device, which in its simplicity is completely inferior counterparts.
Scheme:
The scheme was taken in some of the ancient issues of the journal "Radio" for years, don't remember what exactly. Was assembled, tested in the case.
Main features:
Nominal input voltage, V 0,5 Input resistance, not less, com 70 To transfer voltage 1 Harmonic distortion, % 0,05 Signal/noise ratio, dB 80 Consumption current, mA 7
The width of the stereo is regulated by a variable resistor R1. On the right side of the engine - the stereo base is minimal and the result is a monaural signal. In the left position of the stereo base is expanded twice.
The scheme is not critical to detail, however, the variable resistor is recommended to use a slide, type JS3-23B. Connects this device, for example, between a pre-amplifier and power amplifier.
It feeds the stereo expanderfrom bipolar stabilized power supply voltage +/-15 volts.