Portable mixer (2)

PORTABLE MIXER 2 This second part in the series continues with the construction of the first output module, which incorporates tone controls, an output level indication and a balanced as well as an unbalanced line output. by A Schmeets As explained in the preceding article (Elektor Electronics, April 1986), there are two output modules to the portable mixer: one for general usage, and one for more specific applications, incorporating a monitor and effects amplifier, as well as a parametric equalizer sec- tion. The former is described below, whereas the latter will be discussed in next month"s issue. The circuit The circuit diagram of the first output module is shown in Fig. 1. Opamps Ai and Ai" are summing amplifiers for the left and right channel respect- ively. The active tone control section of each channel consists of a number of R-C networks in conjunction with an operational amplifier. Note that the tone control potentiometers are stereo types to ensure identical and simulta...