(resolved) What is this EQ op amp arrangement? Servo amp

[ELS122]

What is that arrangement called with the lower op amp?

[Terry Bites]

There is servo action that tends to cancel the DC offsets of the upper amp circuit.

If you had a Vos of 4mV and gain of 100 you'd end up with 0.4V DC at the output.
Audio opamps tend to have substantial bias currents adding to your offset woes.
That's going to create a problem for the next stage.

The lower amp is a non inverting integrator.
This set up emulates AC coupling without putting big caps in the signal path.
You'd usually want a big cap between the inverting terminal resistor and ground, so that cap is eliminated as well.
The integrator sets the high pass corner of the LF response too. I cant read the values so it not exactly clear what the response would be.

You might want to use a precsion amp for the servo and a high offset voltage but good audio amp for the main signal path.
That gives you the best of both worlds, but its probably a bit of a BS circuit from a phile.

[ELS122]

There is servo action that tends to cancel the DC offsets of the upper amp circuit.

If you had a Vos of 4mV and gain of 100 you'd end up with 0.4V DC at the output.
Audio opamps tend to have substantial bias currents adding to your offset woes.
That's going to create a problem for the next stage.

The lower amp is a non inverting integrator.
This set up emulates AC coupling without putting big caps in the signal path.
You'd usually want a big cap between the inverting terminal resistor and ground, so that cap is eliminated as well.
The integrator sets the high pass corner of the LF response too. I cant read the values so it not exactly clear what the response would be.

You might want to use a precsion amp for the servo and a high offset voltage but good audio amp for the main signal path.
That gives you the best of both worlds, but its probably a bit of a BS circuit from a phile.

Why not instead just connect the 494ohm resistor instead of ground, connect it to a slightly positive voltage, to cancel out the offset voltage.
You could use a trim pot too and dial in the offset voltage.

Does the offset voltage change with supply voltage linearly or no? How does it change with temperature?

[TimFox]

This circuit is used to combine a high-speed op amp (with mediocre offset drift) with a low-drift op amp (with low speed) to automatically remove the DC offset drift while obtaining high speed.
Years ago, a mechanical chopper was used to obtain the low-drift amplifier channel.

[Terry Bites]

Exactly sir.