江湖英雄召集令--史上指标最好的Benchmark的前馈纠错电路
本帖最后由 vodkafu 于 2020-12-26 11:38 编辑Benchmark AHB2 在ASR网站已经独霸功放指标排行榜两年了， 国内没见有卖的，所有的国外评价都给了好评，得奖无数。
https://www.audiosciencereview.com/forum/index.php?attachments/benchmark-ahb2-amplifier-audio-review-jpg.26573/
https://www.audiosciencereview.com/forum/index.php?attachments/best-class-d-amplifier-review-png.100359/
5w@8欧 时THD指标达到了惊人0.00022%， 185瓦时更降低到0.00016%
https://www.audiosciencereview.com/forum/index.php?attachments/benchmark-ahb2-amplifier-power-at-4-ohm-compared-to-hypex-nc400-audio-measurements-png.26579/
我在网上陆续找到一些线索，Benchmark 的工程师说明了他们拿到了THX的专利授权，使用了THX的前向反馈电路，用于纠正AB类输出级产生的失真，指标好不说，至少诟病深度负反馈的瞬态失真的人们没话可说了。
Benchmark的VP和首席工程师原文
This is John Siau, VP and chief engineer at Benchmark
The THX patents are:
8,004,355
8,421,531
The patented topology uses feed-forward error correction to virtually eliminate crossover distortion. The technique is so effective that the output stage can be run in class-B operation while achieving very low distortion. This also allows class-H or class-G tracking rails without the usual distortion problems associated with these designs. THX has demonstrated a design that rivals the efficiency of class D amplifiers.
The THX topology was interesting to Benchmark for an entirely different reason:
The same feed forward error correction can be used to remove crossover distortion from a class-B amplifier can be used with class AB biasing to create an amplifier with extraordinarily low distortion.
Our goal was to achieve very low distortion, with a focus on low crossover distortion. We were willing to increase the power dissipation as much as necessary to optimize the distortion performance. The optimum solution uses some bias current, but much less than a traditional class AB. Distortion of the AHB2 is at the measurement limits of our AP 2722 and 2522 test stations.
The THX topology also allowed us to utilize two power supply rails in a class-H (or G) configuration without any measureable distortion penalty.
The AHB2 is significantly more efficient than a traditional class AB, and has much lower distortion. Power consumption is only 20W idle. A traditional class-AB of equivalent power would consume 100 to 120 W idle. For example, the similarly sized Bryston 3B consumes 120W idle.
Benchmark chose to build the amplifier with very low gain. Gain is only 9 dB instead of the more typical 20 to 30 dB gain found in most power amplifiers. This means that the AHB2 clips with a 22 dBu input instead of an 8.2 dBu (2 V RMS) input. The AHB2 is designed to accept studio-level input levels and this can significantly improve noise performance between connected devices. In my opinion, most power amplifiers have far too much gain.
Our design goals included a 130 dB SNR relative to maximum output. To achieve this performance we used very low impedances, and some very unique PCB layout techniques. We also chose to use a switching power supply so that we could eliminate 60 Hz magnetic components. The magnetic fields produced by a high frequency switching supply are much lower and are out-of-band.
We also chose a tightly regulated power supply. Most power amps use unregulated supplies because this is the most efficient use of resources if switching supplies are not used. Given switching supplies, tight regulation comes almost for free. Better yet, the power supply control loop can be made fast enough to react to all audio frequencies. The AHB2 does not rely on secondary capacitive storage.
We will be posting performance plots and measurements on our website soon.
__________________ 本帖最后由 vodkafu 于 2020-12-26 11:34 编辑
关于THX的专利原文可以在这里看到：
**** Hidden Message ***** 我研究了一下THX的专利，并做了仿真电路，有一定效果，但距离使用还有很大的距离，另外看到AHB2 只是用了专利，但并没有照搬。
所以斗胆请论坛里的各位大侠，一起来破解这个史上最佳功放的秘密。
**** Hidden Message ***** 就箅发错，我也进来坐一次沙发
:) :victory: 江湖英雄召集令--史上指标最好的Benchmark的前馈纠错电路 {:3_75:} 来学习
:dizzy: 估计开关电源的设计是个亮点 来学习 学习 前馈纠错电路，学习学习！ THX代表是器材. 感兴趣，看看 看看 :) 前来学习报到。 先画出电路图来看看就知道了
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