Merge pull request #2122 from tzz-radxa/docs/rock4d-speaker-amp-note-20260916

docs(rock4d): note that the speaker amplifier is not populated

Author: Milir-Radxa

docs/rock4/rock4d/hardware-use/headphone.md

@@ -97,6 +97,16 @@ sudo aplay -Dhw:1,0 /tmp/tmp.wav
 详细接口规格参考下载专区的 [硬件设计 : 原理图](../download)
 :::
 
+:::note
+ROCK 4D 出厂默认**不焊接扬声器功放**。下表中的信号来自主板上预留的扬声器功放电路：功放芯片、喇叭座及其外围元件（磁珠、滤波电容等）出厂均未贴（NC），因此「扬声器预留焊盘」**无法直接驱动扬声器发声**。
+
+如需外接扬声器，可参考以下方式：
+
+① 通过 3.5mm 耳机插孔连接有源音箱（耳机插孔可直接驱动 32Ω 耳机）；
+② 外接功放模块，从预留焊盘取出 `AUD_LINEOUT_L` / `AUD_LINEOUT_R` 模拟音频信号；
+③ 自行补齐预留的功放电路（功放芯片、`VCC_SPK_AMP` 供电、`SPK_CTL_H` 使能及输出滤波元件）后，再连接扬声器。
+:::
+
 | 左声道 Pin# | 左声道 Name   | 右声道 Pin# | 右声道 Name   |
 | :---------: | :------------ | :---------: | :------------ |
 |      1      | SPK_CTL_H     |      1      | SPK_CTL_H     |

i18n/en/docusaurus-plugin-content-docs/current/rock4/rock4d/hardware-use/headphone.md

@@ -97,6 +97,16 @@ sudo aplay -Dhw:1,0 /tmp/tmp.wav
 For detailed interface specifications, please refer to the [Hardware Design: Schematics](../download) in the download section.
 :::
 
+:::note
+The ROCK 4D **ships without the speaker amplifier populated**. The signals listed below come from the reserved speaker amplifier circuit on the board: the amplifier ICs, the speaker connectors and their peripheral components (ferrite beads, filter capacitors, etc.) are left unpopulated (NC) in production. Therefore the "Speaker Reserved Pads" **cannot drive a speaker directly**.
+
+To use an external speaker, you can:
+
+① Connect powered speakers to the 3.5mm headphone jack (the jack can directly drive 32Ω headphones);
+② Use an external amplifier module, taking the `AUD_LINEOUT_L` / `AUD_LINEOUT_R` analog audio signals from the reserved pads;
+③ Populate the reserved amplifier circuit yourself (amplifier ICs, `VCC_SPK_AMP` supply, `SPK_CTL_H` enable and output filter components), then connect the speaker.
+:::
+
 | Left Channel Pin# | Left Channel Name | Right Channel Pin# | Right Channel Name |
 | :---------------: | :---------------- | :----------------: | :----------------- |
 |         1         | SPK_CTL_H         |         1          | SPK_CTL_H          |