# How to calculate gain of opamp with Max446 chip?

I just wondering how do you calculate the gain of the amplifier in a circuit like this: I am familiar with gain calculation on non-inverting and inverting opamp but am having trouble with this.

Any help would be appreciated.

This is actually a non-inverting op-amp with a pass band filter and a DC offset cancellation.

The formula is

Av = 1 + R2 / R1

Where the resistor are the 100k and 10k, so you would get a gain of 11.

• The first group with 1 cap and 2 1Mohm resistor are a high pass filter and decoupling.
• The 100pF below the chip is a low pass filter.
• The 1uF below the 10k resistor is there to remove DC offset.
• so that means that it will always have a 2.5v input? – Newbie Sep 30 '18 at 1:21
• If the input bias current is zero (the input ESD structures have low leakage, and the input transistor is JFET or MOSFET), then YES. – analogsystemsrf Sep 30 '18 at 1:54
• @analogsystemsrf wouldn't that mean that the output will always be 27.2V? – Newbie Sep 30 '18 at 2:12
• That's the purpose of the 1uF cap, to remove DC offset, so only the signal will be amplified. I guess this is a solution to be able to use a single rail supply. The output cannot be higher than the opamp supply voltage. – Damien Sep 30 '18 at 2:15
• @Damien so just to be clear this circuit can be used to amplifier the human voice to used in an ADC? – Newbie Sep 30 '18 at 2:19