Electronic – Missing connection in amplifier example

The closed gain of this amplifier is 38dB so it only needs a small input (a few mV) to give the output required. As Andy has already commented (+1) its not an op amp. It doesn't require any DC input as the internal circuit is already connected.

There is a mistake on this diagram. C1 should read 100nF and is there to take out some of the high frequency hiss noise. As with all decoupling capictors it should be connected as closely as possible to the chip pins.

Finally add an input capacitor (value will set the low frequency cut off). A 1uF non polarized tantalum should cope with most situations.

Given the vastly changed info... TDA2822 is a low power chip (under a 1W; its datasheet recommends it for "portable cassette players"), and of course the speaker it sends to is only 2.5W (doesn't get that much). Basically you can take the output of this amp (from the speakers' wires) straight to any professional line in audio equipment. It's like plugging in a walkman. No divider or anything like that is needed. Professional equipment accepts "hotter" signals than the consumer ones; see line level. Check with a voltmeter just in case that you don't get way over (say no more than 2V RMS on whatever it blasts the loudest), but there's not much else to do.

Also the quality of the PCB isn't great... but do you want NASA standards in toy using a $0.10 chip? The last image are "mouse bites", but those are normal.

Regarding the power supply info (added in a comment): 7.5V is how they get this chip to make enough sound for a loudspeaker. Likely the TDA2822 output doesn't get to the rails (i.e. it's less than 7.5V peak); most amps can't swing all the way to the rails, typically they can go up to 1V or 2V under. Some of the more dinky mixing consoles I've seen the innards of have only 6.3V rated caps on inputs; that mixing console was powered from 6V. So... there's potential danger of damaging a mixing console over a long period of time if this toy outputs to its max volume; we're not talking about immediate fireworks. If the mixing console is powered by more than 6V supply chances are good it uses higher-rated caps on inputs so the danger of damage becomes practically nil. If the mixing console is a profi one it will have maximum input level somewhere in its (service) manual. For example, a TASCAM I have specifies maximum input level as +18dBv (8 V).