Ramsey Electronics UAM4 Manual page 6

it. Balanced signal lines are mainly used in professional equipment and
signals that are run through very long 'transmission' lines.
If your audio source is un-balanced, this means only one of the input lines,
(either the '+' or '-') is used, and the other is simply tied to ground. Usually the
'+' line is used and is called the non-inverting input. This means that when the
signal on the input increases with respect to ground the '+' terminal on the
speaker output will increase with respect to the '-' speaker terminal for that
channel. If the '-' input terminal is used the output will be just the opposite.
For most home audio applications this really doesn't matter as long as both
inputs and outputs are connected the same way. See the "USING YOUR
UAM4 AMPLIFIER" section later in this manual for more information about
connecting the inputs and speakers.
Getting back to the circuit, the input signal is applied to the MAX9708 through
capacitors C1, C2, C3, and C4. These capacitors are called coupling
capacitors, and are used to isolate the MAX9708 inputs from any possible DC
levels that might appear on the input signal lines and allow the actual signal,
which is an AC signal, to pass through.
Once the signal reaches the MAX9708 there isn't a lot more to say, other than
it performs the "magic" of increasing the power level of the signal (as
explained earlier, by converting it to a bunch of pulses and turning on and off
the output transistors) letting you connect to the speakers and hear the
music. The speakers are connected to the output terminals shown in the
upper right corner of the schematic.
What follows is an interesting little side note about the output signal for those
of you that might want to look at the output with test equipment. If you place
an oscilloscope on the output terminals of the UAM4 you won't find a nice
clean looking signal... In fact it will look like a lot of noise! Fear not, because
this is what it is suppose to look like. Remember that the signal is actually a
modulated square wave that changes in proportion to the signal. The signal is
even more 'messed up' because in the factory default spread-spectrum mode
of operation the frequency used to switch the output transistors is actually
changing up to +- 4% around the center frequency of about 200kHz. This is
done to help reduce the interference produced by the output stage transistors.
This, along with other factors, is why there are not any large filter components
needed on the UAM4. The speakers, because they are an electro mechanical
device, also act as a sort of filter and end up producing a nice clean audible
reproduction of the applied input signal.
That's it as far as the basic operation of the UAM4. But what about all those
other components on the schematic? Well lets take a look at them! Most of
them are used to configure the MAX9708. First look for a label just to the right
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