自制耳机放大器
看了半个月的模拟电路，今天做了第一个模拟电路的玩具 -- 一个耳机放大器~
其实这个电路是驱动低阻的无源音箱用的，但是手上没有：（。
电路板早就打样了，只不过今天中午才收到，下午焊上测试了一番，效果相当不错~ ：D
左声道原理图（右声道相同）：
大牛们请无视，因为目前就学习到这里，所以只能弄出这样的电路，并且基本是抄书。
5V 就可以工作，高了更好，只要不超过电容的耐压值，3.8V 以下就要被削波了。15V 下驱动 8 欧负载理论上可以输出 0.5w 以上。
成品：
使用兆信的稳压电源输出 5V ~ 15V、电池（4x1.5v）、USB 电源（再经过自制的稳压器），都可以很稳定的工作。
手上只有 ER4p 和 HD570 这两个耳机可以测试，都不难推：（，所以只能测试下音质效果。测试下来效果令人满意~ 原来曾经用过一个铁三角的廉价耳放，听上去效果没什么差别 ：D。
总结：
无信号下噪声很低，是因为只有一级放大的缘故。不过插上耳机，还是会听到一些“沙沙”的噪声，主要来自信号线和音源的噪声，因为前级的电压放大把噪声也放大了，铁三角的那个耳放也有同样的现象。这个看来只有改善传输线和音源的品质才行。
原理图中的 C11 就是高音增强电容，想增强高音，就增大这个电容，不过太大了就没意义了（因为全增强了）。如果你的耳机高频很突出，那么可以不要这个电容，不过大部分情况下还是需要的。我开始听的时候，觉得高音太刺耳了，所以就认为 470uF 太高了，后来换成 10uF 的感觉不错，但是最后才发现是因为播放器的 EQ 把高音区打得太高了，把 EQ 调成水平，然后再换回 470uF，就正常了。拿掉这个 470uF，感觉很浑浊。
相比在播放器上用 EQ 拉高高音，使用电容调整的效果就要自然多了，这次自制耳放最大的体会就是这个。但是缺点也是有的，因为噪声也在这个频率区域，所以用电容调整，噪声也会变大：（，用 EQ 就不会有这种状况了。
C8 和 C6 是输入和输出的隔直电容，输入是 10uF，输出是 1000uF。实验的时候犯过一个错误，就是把 C6 也换成 10uF 的，结果发现低音全没了。后来才知道，为什么这两个电容不一样，是输入和输出阻抗不同造成的。
输入阻抗是 R7 和 R9 并联的值，大概 10K 左右，配合 10uF 的 C8，截止频率在 1.6Hz 左右（
），对低音信号（最小 20Hz）完全没问题。
输出阻抗其实是耳机的阻抗，比如 ER4p 是 27 欧，配合 10uF 的 C6，截止频率就在 590Hz 左右，自然低音都没了。换成 1000uF 的，到 5.9Hz 就没问题了~
下一步：
这次用的元件都是非常廉价的，第一级的三极管是最便宜的 2N5551，后面的推挽输出也没有配对，随便抓了个 TIP31C 和 42C 来用，电容也都是论斤卖的那种，所以下一步就是更换好一点的原件，看看音质上是不是有提升，也可以一定程度上了解那些音响的“磨机”有没有意义。
另外，这个电路板是上个星期五去打样的，周末出差，回来之后继续看晶体管的书，就看到了负反馈放大和差分放大，后悔没有加在这个电路里面。那么，接下来就是设计更有技术含量的电路吧，看看可否改善音质。
一般的功放，似乎前级的电压放大都是 OP 来实现的，既省空间又稳定。但是我也用 OP 就不好玩了，那么就尝试用分离元件搭个 OP 吧，正好书上也有这部分的内容，看看效果咋样 ：D。
2010年1月28日 06:06
一点都看不懂.....:呵呵
2010年2月04日 19:42
比较好奇电路板是哪里打的呀? 价格多少?
2010年2月05日 13:52
@TLHL28: 跨行了嘛 :D
@lanwellon: 100 多的开板费，打板的工厂到处都有，淘宝上一搜一大堆 :D
2010年10月17日 20:15
膜拜一下，想和楼主讨论一下耳放的问题可否
2010年10月18日 03:07
当然没问题～ :D
2010年11月14日 23:04
第一级的两个三极管都是2N5551么，后面那两个管我用C2073和A940配对就可以了吧
2010年11月14日 23:27
可以的，一级的三极管上面电流很小，一般的小封装三极管都可以胜任~
2010年11月14日 23:39
好吧，那我就选用第一级两个2n5551好了，我还是没明白为什么你的板子上有3个大的管
2010年11月15日 00:38
前级电压放大用小管，后级电流放大因为流过三极管的电流会很大，所以得用大管，小管的最大 Ic 只有 100mA 左右吧，如果后级用小管很容易就烧了~
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