工具与资源spectrum.ieee.org
以还算便宜的成本自制专业级音频放大器
Build Your Own Professional-Grade Audio Amp on the Sort-Of Cheap
2018 — 2020，它一次次回到首页
黑点是上首页（≥ 50 分）的那次投稿，空心点是没冲上去的投稿，点越大分数越高。
导读
IEEE Spectrum 的 DIY 教程，教读者以相对低廉的成本自制一台专业级音频功率放大器，涵盖电路设计与搭建要点。文章多次登上 HN 首页，引发关于功放设计、D 类功放崛起和发烧友文化的讨论。
为什么经久不衰：它把专业音频放大器设计拆解成爱好者可以动手实现的项目，而评论区补充了从电路安全到 THD 指标局限的实用知识，至今仍是音频 DIY 的入门参考。
HN 评论精选
高价发烧设备与'无染色'目标自相矛盾，但亲耳听过顶级系统后承认其体验确实惊人
发烧友文化充满矛盾：追求无染色的高保真，卖天价的却往往是带宽有限、失真高达 5-10% 的电子管设备。我叔叔在达拉斯结识了一群花几十万美元买音响的朋友，我曾亲眼见到一套价值六位数的系统——Focal 旗舰音箱、750 瓦电子管功放、深度改装的唱盘和开盘机。说实话，那声音确实震撼。我确信 90% 是安慰剂效应，但很高兴能亲耳听过。
S_A_P查看英文原文
Audiophilia is a study in contradiction. The ask is a flat "uncolored" accurate sound. The gear that sells for ridiculous prices is usually tube gear with limited bandwidth and makes ~15 watts at 5-10% (admittedly usually even order harmonic) thd. Hardly uncolored. That said, and Ive mentioned this before on HN. My (now late) uncle had a bunch of audiophile friends in Dallas. He hung around folks who had spent upwards of 500,000 (yes you read that right) on audio gear. I can't forget the time I rolled up to a modest middle class home, only to find out that inside of this house was a pair of Focal Grand Utopias (selling retail for 250k at the time, though he said he paid around 60k for the pair). He had 2 750 watt tube amps, current era but the brand escapes me. For source material he had a heavily modified Technics SP-10 with 2 tone arm/cartridge combinations and a boutique tube phono preamp. This fed into a similarly heavily modified Dynaco tube preamp from the 1960s. When he really wanted to get serious, though, he had a studer 2" tape machine and a sizable collection of low generation master tape copies. If I hadn't seen this with my own eyes I would say my uncle was full of shit when he told me about it. You know what? it sounded freaking amazing.Im sure it is 90% placebo, and 10% the fact that he was able to play high bandwidth audio to concert levels with no stress or strain from the amplifiers. Was it worth 6 figures of money? not to me. But I am glad I got to hear it...
从专业工程角度指出该设计缺少限流、保护电路等关键安全设计，'专业级'名不副实
图中的功放远达不到'专业级'。专业意味着在恶劣输入、恶劣输出、恶劣市电、满功率户外运行等异常情况下都能正确工作。该设计缺少大量安全特性：200VA 变压器配 350W 功放会导致变压器过热甚至起火；整流桥尺寸不足，传统工频整流中二极管峰值电流可达平均值的十倍以上；还缺少扬声器保护、浪涌保护和输入端射频干扰滤波等。
tuatoru查看英文原文
The amp shown is nowhere near "professional grade". Professional means it does the right thing in unusual circumstances - naughty inputs, naughty outputs, naughty mains power, running at full power on the grass under a pile of coats and scarves, pumping through old and fraying speaker leads lying on the ground, ... The design is missing all sorts of safety features apart from the most basic (prevent electrocution from broken mains wires touching the chassis). A 200VA transformer with a 350W amplifier is just asking for a transfomer meltdown (or fire, if the transformer doesn't have a functioning thermal fuse), unless there is a limiter in place to limit the output to 120W or less. (Fuses are also recommended, but in the professional environment you don't want them to blow, ever. Hence, a limiter is mandatory.) The bridge rectifier is undersized. In traditional mains-frequency rectification such as shown, the diodes only conduct for about 10% - 20% of the time, so the peak current in them is can be more than 10 times the average. At 36V and 10A output average, the rectifier current peaks are in the neighbourhood of 100A. A BR35 (35A 1000V) will provide a reasonable working life. At up to 36W dissipation, you can probably just bolt it to the chassis with some thermal compound. The design is also missing speaker protection features and surge/spike protection/EMI prevention, and RF intereference filters on the inputs. The design is also missing convenience features one expects of a professional amp, such as "power good" and "fault" lamps/circuitry. And handles. It's nice that there are good inexpensive amplification modules now. But as with software, the difference between a toy example and professional grade is thought, time and money spent on reliability, safety, and usability.
D 类功放已全面胜出，廉价成品板让自制功放的意义下降
如果不想自己动手，TPA3250 功放板在常见廉价渠道不到 100 美元就能买到。D 类功放的胜利已是全面的：无需极致的电路板布局或昂贵的稀有元件就能实现极低失真，从 AirPods 到手机都在用，几十瓦的功率单芯片即可搞定。
pjc50查看英文原文
If you want TPA3250 amps without having to build your own, they're widely available from the usual cheap vendors for less than $100. The victory of class D is now total; extremely low distortion numbers can be achieved without heroic board layout or expensive passives made of unobtanium. All available in the tiny packages of AirPods, smartphones etc. And power levels in the tens of watts can be done with a single chip.
科普 THD 指标的局限：谐波分布比失真总量更能决定听感
THD（或 THD+N）并不总是比较两台功放的有效指标。失真更差的功放可能实际更优，因为其失真集中在低阶偶次谐波，而标称 THD 更低的功放可能在奇次或高阶谐波上失真更多。失真在各次谐波上的分布与总量同样重要——这就是电子管功放标称 THD 偏高却依然好听的原因。
xenocyon查看英文原文
Since this isn't explicitly clarified in the article, it's worth mentioning that THD (or THD+N for that matter) is not always a helpful spec to compare two amps. You can easily have two amps where the one with the worse THD is actually the superior one because its distortion is in low-order even harmonics, while the nominally lower THD amp has more distortion in odd or higher-order harmonics. The distribution of distortion over harmonics is as important as the raw sum. (For the layperson who doesn't care about the math: this is why tube amps sound good even when their nominal THD spec may be higher than low-end solid-state amps.)
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