104 Nicolas Collins
Chapter 27: Mixers, Matrices and Processing
You will need:
- An assortment of sound-making circuits, found or made.
- A few pots of the same value (c. 10KOhm - 100kOhm).
- Assorted resistors.
- Some solid and stranded hookup wire.
- Assorted jacks and plugs.
- An amplifier or two.
- Soldering iron, solder and hand tools.
Mixers
Now that your collection of noisemakers is growing, a simple mixer might prove
useful. Here is a completely passive circuit -- it uses no batteries, needs no
on/off switch or circuit board. Even if you already have a “real” mixer, this is a
very convenient way to expand the number of inputs.
The basic schematic is shown in Figure 1. The signal (i.,e., tip) of each input jack
is connected directly to one ear of a pot. The center tap on the pot (nose?) is
soldered to a 10kOhm “summing” resistor. The non-pot ends of all the summing
resistors are tied together and connected to the signal/tip of the output jack. The
ground/shields of all the jacks are connected together and soldered to the other
ear of all the pots -- this common bus is indicated by the ground sign. Figure 2
shows which ear to use for input and which for ground if you want a traditional
mixer feel (ie, turning the knob clockwise raises the level.) You can expand this
circuit for any number of inputs by simply adding another jack, pot and resistor
for each additional signal.
Figure 1 Figure 2