The common (ground) connection for the batteries (minus side of the + battery supply and plus side for the - battery supply) and any other circuitry would be the common (coax shield, outer part of an RCA connector, or inner-most contact on a phone plug) of the audio connection.

Make the circuit on a printed circuit board, stripboard or perforated board. Connect everything that is shown grounded together. The input and output also have ground wires. The two batteries are connected in series and their junction is connected to ground.

Or make the circuit with a single polarity supply as was shown.

Originally Posted by audioguru

The OPA2244 has even lower power supply current than the lousy old LM358 dual and LM324 quad low power opamps.
But those old opamps have pretty bad crossover distortion so maybe the OPA opamps have even more crossover distortion?

The LM358 and LM324 low power opamps have a very low max frequency at full output level.
The OPA opamps also have a low max frequency (950Hz) at full output level which misses most of the range of audio frequencies.

Those are some good concerns about frequency response and distortion.

The slew rate is typically 0.1V/µS which gives a maximum frequency response of 16kHz at ±1Vpp, which should be adequate for most casual listening requirements. There isn't usually that much high frequency energy in music.

There's no data in the data sheet about crossover distortion, so I can't answer that concern.

All op amps are different. There are differences in minimum and maximum voltage ratings, current used, frequency response, slew rate, and whether their inputs and outputs operate at the power supply rails (rail-to-rail). You have to look at the data sheets to determine their capabilities and limitations, and then determine the best for your particular requirements.

Suggest you read a tutorial on op amps such as Operational amplifier - Wikipedia, the free encyclopedia to learn more about them.