Tone Control C828 with Subwoofer it is Mono Circuit Tone control with using C828 transistor its very powerful tone control circuit because by adding Subwoofer output on tone control. See circuit schematic below.
You can using this tone control in stereo amplifier by adding 1 more tone control mono circuit to stereo. Power Supply need 15 -18V Asymmetric Voltage supply. This ton control is matched for Mic Pre-Amp 4558. See this Project