This is a design for linear optocoupler is built with MOC5010 and can be used to isolate a circuit from main grid, audio interface, in medical electronics and many other applications. Because of its high isolation resistance (1011 Ω), MOC5010 is used in applications where a circuit is powered directly from main power. With a bandwidth from 5 Hz to 100 kHz you have no reason to complain about audio signal response. This is the figure of the circuit.
MOC5010 transforms an input current variation into an output
voltage variation. The linear optocoupler circuit presented here has an
amplification factor of 0.75. The input must not overcome 2 Vef while bandwidth
is 118 kHz at -3 dB.
Amplifier A has a transfer resistance of 200 mV/mA resulting in
a total amplification of 0.6 … 0.8 (-4.5 … -2 dB). The output impedance is not
higher than 200 Ω so you can connect an external amplifier at pin 4. If the
input voltages are higher than 2 Vef then connect a potentiometer as voltage divider.
If the global amplification is too small use a
regular transistor instead of FET T1. It is important to mention that 2
separate power supplies are required: both the +12 V terminals as well the 0V
(ground) must be isolated from one another. In many cases it is possible to use
a 12V voltage for the transmitter part from the connected device.
