R9 = 2K - 1/2W Trimmer Cermet (See Notes) An astonishing feature of this design lies in the fact that a complete stereo mixer as shown below in the Block diagram draws less than 6mA current! Obviously this layout can be rearranged at everyone wish. The image below shows a Block diagram of the entire mixer featuring four Input Amplifier Modules followed by four in-out switchable Tone Control Modules, one stereo Line input, four mono Main Faders, one stereo dual-ganged Main Fader, four Pan-Pots, a stereo Main Mixer Amplifier Module and two further Tone Control Modules switchable in and out for each channel, inserted before the main Left and Right outputs. Main Mixer Amplifier Module: a stereo circuit incorporating two virtual-earth mixers and showing the connection of one Main Fader and one Pan-Pot. It can be inserted after one or more Input Amplifier Modules and/or after the Main Mixer Amplifiers. Tone Control Module: a three-band (Bass, Middle, Treble) tone control circuit providing unity-gain when its controls are set to flat frequency response. Input Amplifier Module: a low noise circuit equipped with a variable voltage-gain (10 - 100) preset, primarily intended as high quality microphone input, also suitable for low-level line input. The mixer is formed assembling three main modules that can be varied in number and/or disposition to suit everyone needs. The target of this project was the design of a small portable mixer supplied by a 9V PP3 battery, keeping high quality performance. High-quality modular design, 9V Battery powered - Very low current drawing
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