Audio amp question

[Szewczykm]

In another post I explained that I'm troubleshooting some buzz on a pinball machine sound board.  Looking at the schematic, I'm curious as to why the designer did something.  I'm very new to signal amplification so I apologize for my ignorance here.

Attached is a schematic with some notes and the signal path highlighted in red.

Audio leaves a DAC (TDA1543) and is fed into an LM833N op amp.  The signal leaves the op amp, presumably amplified, and then enters an SSM2024 Quad audio amplifier.  It leaves the output from the SSM2024 and enters *another* LM833N.  The signal then leaves the LM833N and continues out to the power amp.

I'm wondering why there are all of those amps in series before hitting the power amp.  Is it that there is a point where the gain is too high and it gets noisy, so you just feed one into the other until it's "loud" enough for the power amp?  Or is there something I'm missing where one is amplifying and one is filtering or something?

EDIT: Also, can you tell me what C55 (just before the IN on U31) is doing?  I'm guessing it's a filtering cap, but not sure what or why.

Thanks for your input.

[ciccio]

This is a very standard configuration. Some (20?) years old.
The SSM2024 is a quad "current controlled amplifier", that means is an amplifier that has is gain controlled by an external current (or voltage) signal.  You did not post the whole schematic, so I can't tell how the audio gain is controlled.
Datasheet is here http://pdf1.alldatasheet.com/datasheet-pdf/view/92296/ETC/SSM2024.html
It needs to be driven by a low impedance source, thus the 200 ohms resistor from input to ground, and it's output is a "current", so it needs to be converted in a "voltage".
The first op-amp is needed for integrating the DAC output, then it drives the SSM2024 whose output "current" drives the inverting input of the second op-amp.
The second op-amp output "voltage" signal drives the power amplifier.

The power amplifier is a single supply device, so it's input is at about 1/2 VCC.
The op-amp is powered by a dual supply (plus/minus), so it's output pin DC level is  zero volts (GND potential)
Without C55 a DC current will try to flow from power amplifier input into op-amp output, resulting  in some certain malfunction.
C55 will block this DC current flow, but will allow AC signals to pass.
Best regards