DC Mixer Components (Fig. 19)
Resistors (all 1/4 watt 5%)
R 101, 102,103 100k
R104 3k9
R105 10k
Potentiometers
RV101,102,103 10k Lin
Semiconductors
IC101 741C
Miscellaneous
Circuit board
Three control knobs
Wire, solder, etc.
Extendible Mixer
With a simple, single VCO synthesiser there is only one audio output signal, but with a de ' sign that incorporates two or more VC0s, plus perhaps a noise source as well, there will be several audio signals which must be mixed together to give a single audio output. All that is needed is a basic summing mode mixer such as the design shown in the circuit diagram of Figure 20. As shown in Figure 20 the mixer has three inputs, but if only two are required it is merely necessary to omit RVI03, C103, and R103. If more inputs are required this can easily be achieved. Just add an extra input resistor, DC blocking capacitor, and level potentiometer for each additional channel. In theory any number of extra channels can be added to the circuit, but in practice problems with noise pick up might be experienced if a large number are used. In the present application no more than about five inputs should be needed though, and this number should certainly not result in any problems.
Extendible Mixer Components (Fig. 20)
Resistors (all 1/4 watt 5%)
R101,102,103,104 47k
Potentiometers
RV101,102,103 47k log
Capacitors
C101,102,103 470nF miniature polyester
C104 10uF radial electrolytic
Semiconductors
icioi 74IC
Miscellaneous
Circuit board
Three control knobs
8 pin DIL IC holder, wire etc.