Texas Instruments MIXED SIGNAL PRODUCTS TPA0103 - Manual (Page 20)

The TPA0103 Audio Power Amplifier Evaluation Module
3-6 Details
3.2.3 Inputs and Gain
The left and right single-ended channels remain separate from input to output.
On the TPA0103 EVM board, the left and right channel inputs are mixed to
produce a monaural representation of the stereo signal and applied to the
amplifier IC center channel input.
Each of the left and right channels has two separate signal inputs. They are
called
line and headphone (HP ) and are pin-selectable. The line inputs and
the center channel input are adjustable between approximately 2 and 22, and
the headphone inputs are fixed at a gain of 1. In the typical application in which
the TPA0103 powers left and right speakers until headphones are plugged in,
the line input gain can be set so that the two inputs provide approximately the
same perceived listening level in the headphones as from the speakers. An
input multiplexor in the amplifier IC selects between the two inputs according
to the state of the HP/LINE IC pin.
The TPA0103 amplifier IC, like most other amplifiers, exhibits its best distortion
and noise performance at lower gain levels (see the TPA0103 data sheet).
Gain versus total harmonic distortion (THD) should be considered in each
application. Both the module input signal level and the TPA0103 module gain
should be adjusted to obtain the lowest overall distortion level for a particular
overall gain. A quick rule of thumb (everything else being equal): the module
input signal level should be as high as possible without clipping or overloading
the TPA0103 input, and the TPA0103 gain should be kept as low as possible.