A 4 channel audio mixer that requires very few electronic components can be built using this electronic scheme based on SSM2024 chip. To obtain a small offset and a high rejection, the four inputs of the 4 channel audio mixer circuit must have an impedance of 200 ohms to the ground. These impedances are resistances obtained with R5-R8, which are part of the voltage divider at each input.
With values of the components from this scheme nominal input signal is 1 V (0 dBV). At this level, distortions are about 1%, and at lower levels do not exceed 0.3%.
Maximum amplification is obtained for a control current of 500 uA, in which case the input control voltage is slightly increased to 0.5 V (result we need a maximum control voltage of 5.5 V).
The amplifier output currents are summed by simply connecting the output pins.
The signal / noise of the mixer is about 90 dB and the bandwidth of the order of 130 kHz.
SSM2024 integrative work satisfactorily with a supply voltage between 9 V and 18 V, but best results are obtained at ± 15 V.