This application report compares two possible blocking or coupling capacitor configurations for stereo headphone amplifiers operating from a single supply voltage. The report demonstrates that the standard two-capacitor configuration can be replaced by a single-capacitor configuration with little or no perceivable difference in sound quality. The primary advantage of a single-capacitor system is that only one large capacitor is required. In many compact multimedia systems like those in personal digital audio players, wireless phones, and personal digital assistants (PDA), these capacitors can be the largest components on the board. Therefore, eliminating one of the bulky coupling capacitors reduces cost and minimizes the area needed on the circuit board.
The report compares the traditional two‑capacitor coupling scheme with a single‑capacitor configuration for stereo headphone amplifiers powered from a single supply. By using only one large capacitor, the design reduces component count, board area, cost, and improves reliability while maintaining comparable sound quality.
Measurements using the TPA102 EVM show that crosstalk is about –6 dB at 20 Hz and drops to –60 dB at 20 kHz for a 32 Ω load, becoming negligible for line‑level loads. The document also discusses ripple‑current requirements and selection criteria for the coupling capacitor.
| Ripple Current per Capacitor (Two‑Capacitor Design) | ≈150 mA |
|---|---|
| Ripple Current for Single Capacitor (Two Channels) | ≈300 mA |
A single capacitor reduces parts count, board area, cost, and improves reliability while providing similar sound quality.
Crosstalk is about –6 dB at 20 Hz and decreases to about –60 dB at 20 kHz for a 32 Ω load, and is essentially negligible for a 10 kΩ load.
The capacitor must handle roughly 300 mA of ripple current because it carries the combined audio current of both channels.