Portable mixer (3)

EE June 1986 62 by A. Schmeets PORTABLE MIXER 3 This concluding article on the portable mixer details the design and construction of the second output module, comprising the monitor; effects-, and headphone amplifiers, as well as the parametric equalizer section. In addition, useful hints are given on how to prepare a fight-weight case to hold the complete set of mixer modules. Output module 2 Fig. 1 shows the circuit diagram of the last module, which incorporates the following sections: • effects output amplifier • PFL amplifier • monitor amplifier with parametric equalizer • one-chip headphone amplifier The amplification of the effects out- put amplifier-Ai-can be set be- tween -6 dB and +14 dB using Pi. Output resistor R30 protects the opamp output transistor in the case of an output short circuit. The PFL summing amplifier-A3-is also a single opamp, whose amplifi- cation (defined with R27) should equal that of A2 and the first output module (see last month"s ...