If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

# OPA134: Line in stage op-amp

Part Number: OPA134

Need help calculate general purpose line in stage op-amp, Inverting op-amp, single Power Supply +12V

This stage should accept input audio signal from various audio line out.

Since line out output levels usually can vary between 0.3 and 1.2  VRMS, depending on impedance, there is no standard, that stage may have no overall gain, i.e. op-amp can work as unity gain buffer (voltage buffer), or can have minimal gain, limited to 2V on the output.

• Hello Wilson,

One option would be to buffer the input to the inverting op amp (output of the audio line out) so that the gain of the inverting amplifier remains constant with all source impedances that will connect to the circuit.

Thank you,

Tim Claycomb

• Hello,

What would be a reasonable input voltage limits for this case?

• Hello Wilson,

The usable input voltage is dependent on the gain of the circuit and Vref voltage. The output voltage is calculated using the equation below.

Vout = Vin (-R2/R1) + Vref (1+R2/R1)

The maximum input voltage would be a voltage that does not cause Vout to go outside the output swing specification of the device. In your case using a 12V single supply the output swing is 2.2V to 9.5V with a 600 ohm load.

Thank you,

Tim Claycomb

• Hi,

Thanks for the help.

Can you advice about Vref: for example, I need Vref = 1.8V: how to calculate a Resistor Voltage Divider between Supply and ground to get this 1.8V?

Thank you.

• Hi Wilson,

The 1.8V for Vref can be generated by dividing the supply voltage down with a voltage divider. There are many calculators available online that will calculate the resistor values for a voltage divider given a desired output voltage and input voltage. Please see the Voltage Divider Calculator offered by TI.

Thank you,

Tim Claycomb

• Hi Tim,

What is Vterm and how to set this?

• Hello Wilson,

There is a lot of information online about how to size components for a design. Please read through Op Amps for Everyone, search our TI Designs, and watch our TI Precision Lab videos.

Thank you,

Tim Claycomb