Texas Instruments TPA0103 manual Inputs and Gain

The TPA0103 Audio Power Amplifier Evaluation Module

3.2.3Inputs 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.

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