"卖油翁"之鹤顶红前级

ch639827608

114# 勇DIY

这不算好电容.
用普通的松下2200U(新的)就很好了,主要还是晶体管和设计问题,分立前不易做好的

分立前级不容易做好应该是有其内在原因的，放大倍数很低，级数多的话，开环增益就大，负反馈就深，负反馈越深就越有高次谐波（见 Audio, Distortion and Feedback   Nelson Pass 11/1/08），
从我仿真过的前级来看，还没有一款前级是各项指标都会好过别的前级的。

下面是JFET的SRPP的一组仿真图，其傅立叶分析很漂亮，但1Hz～200Hz的线性不是很优秀，输出噪声也不是很优秀。100KHz方波马马虎虎。

WKJ

请楼上侠明示.还没有一款前级是各项指标都会好过别的前级的。什么意思,不懂,[

ch639827608

162# WKJ

请楼上侠明示.还没有一款前级是各项指标都会好过别的前级的。什么意思,不懂,[

就是说所有宣称为顶级的前级（我仿真过的，不包括没仿真过的），在几项仿真中都会有一个比较不好的一项（当然不是说那一项很差，只是那一项会比另外一款优秀前级差）。
举例来说，JC-2的傅立叶分析比KAP好很多很多，而其1Hz～200Hz的线性比KAP差好些。
马兰士的HDAM的100KHz方波非常漂亮，但是其傅立叶分析和KAP差不多。Beta22的傅立叶分析也不是很优秀，还远比不上JC-2。
就像众多有名的酒家都会有其各自特色菜。
如161楼所示的JFET SRPP前级，综合性能其实也很不错，线路非常简单，成本低廉。

wscr_wscr

各项指标都好不能代表声音好 还是耳朵验证最实际  应该是找一款大家都公认好声的机子 然后再测量该机子的各指标看看到底各指标都达到的某个值  这样才能取得指标和好声的一个标准

ch639827608

164# wscr_wscr

各项指标都好不能代表声音好 还是耳朵验证最实际  应该是找一款大家都公认好声的机子 然后再测量该机子的各指标看看到底各指标都达到的某个值  这样才能取得指标和好声的一个标准

大家公认，这很难的。
只能够是较多人认为好，例如，很多人认为JC-2很好声。
JC-2的傅立叶分析很漂亮，输出噪声很低，100KHZ方波也不错，就是1Hz～200Hz的线性不是很理想。

卖油翁

如果高次谐波虽差但主要分布在40K以上，我宁愿选择1-200Hz好的！

fzj168

看完不容易,先顶顶,骗些分先....

ch639827608

166# 卖油翁

各人所好。

从

《Audio, Distortion and Feedback》
Nelson Pass 11/1/08

引一段文字

Inter-modulation Distortion（互调失真）
If you like to listen to simple music as played by an unaccompanied sackbutt, harmonic
distortion figures might be perfectly relevant to you, but with a lot of music you will find that
inter-modulation distortion becomes the elephant on the dance floor.
Harmonic distortion is closely related to inter-modulation distortion in that both result from the
same nonlinear distortion of the gain device, but IM distortion reflects what happens when
there is more than one tone involved, and that describes most music. With a single tone,
lower order harmonics such as 2nd and 3rd are not as discernible, and in real life most
instruments (including vocal) contain a fairly rich set of these harmonics anyway. They are
considered musical.
But when two tones are passed through a non-linear device, the amplitude of each of the
tones is altered, or modulated by the other tone. The result is a series of “sidebands”,
additional tones occurring at the sum and difference of the original frequencies. These
additional tones are not generally musically related.
Worse, real music consists of very many tones passing through the nonlinear gain device,
and each of these interacts with each of the others. The result will be very complex, and very
unmusical.

高次谐波多的互调失真较大。

牛耳朵007

继续关注

ch639827608

在

Audio, Distortion and Feedback
Nelson Pass 11/1/08

的最后一段

Conclusion（结论）
Time flies, and there is still much to learn. I haven't really touched on what these pictures
mean to an audiophile, perhaps not what Srajan had in mind when he asked for this piece.
In fact, apart from assuming the preference for low amounts of simple forms of distortion, we
haven't discussed the listener at all. Nevertheless, I am trying to make a point that relates
strongly to the apparent disconnect between subjective experience and simple measurements
of distortion.
We have seen that nonlinear distortion becomes larger and more complex depending on the
nonlinear characteristic of the stages, the number of cascaded stages, and the number of
spectral elements in the music.
Negative feedback can reduce the total quantity of distortion, but it adds new components on
its own, and tempts the designer to use more cascaded gain stages in search of better
numbers, accompanied by greater feedback frequency stability issues.
The resulting complexity creates distortion which is unlike the simple harmonics associated
with musical instruments, and we see that these complex waves can gather to create the
occasional tsunami of distortion, peaking at values far above those imagined by the distortion
specifications.
If you want the peak distortion of the circuit of figure 13 to remain below .1% with a complex
signal, then you need to reduce it by a factor of about 3000. 70 dB of feedback would do it,
but that does seems like a lot.
By contrast, it appears that if you can make a single stage operate at .01% 2nd harmonic with
a single tone without feedback, you could also achieve the .1% peak in the complex IM test.
I like to think the latter would sound better.
© Nelson Pass, 2008

一个只有一级的放大器和一个有不止一级的放大器如果失真完全相同，在听感上，按Pass的说法，这单级的会更好听。

音乐魂

关注、、、看看最终结果！

卖油翁

第二级放弃共射共基，改用差分共基会不会更好？

ebao

第二级放弃共射共基，改用差分共基会不会更好？
卖油翁 发表于 2010-6-3 08:33

还是会有“缺陷”。。。。。。

ch639827608

172# 卖油翁


减少级数听感会更好，
按Pass的说法在同等失真指标下，级数少的听感更好，
millwood也说过类似的话（millwood是放大器设计师，他说他早年也设计过很多复杂线路的总是听感不太好，后来才悟出要简单线路才好声），对于复杂线路，综合指标也很难做好，Beta22就没有公布它的失真频谱测试图。傅立叶分析差的其瞬态互调失真会较大，而这是和听感最密切的。
我买的厂机耳放/前级（3000多元）也是只有两级的，听了6年了，满意。Lite也有三级的石前级，但是是低价产品线路图公开，成品板才100多元（性价比算很高的，我仿真过，综合指标与KAP相当），其2级的是高端产品线路图保密。
两年前用洞洞板接的B1只有一级，驳接功放的效果绝不在此耳放/前级之下。
因此我现在，听耳机用耳放，听音箱用B1驳接功放，各司其职。

卖油翁

172# 卖油翁


减少级数听感会更好，
按Pass的说法在同等失真指标下，级数少的听感更好，
millwood也说过类似的话（millwood是放大器设计师，他说他早年也设计过很多复杂线路的总是听感不太好，后来才悟出要简 ...
ch639827608 发表于 2010-6-3 10:56

太简单的前级其级间阻抗匹配和输出阻抗不佳！

ch639827608

176# 卖油翁

太简单的前级其级间阻抗匹配和输出阻抗不佳！

我的耳放只有2级，50欧姆阻抗的耳机推得很好，50欧姆，功放有这么低的输入阻抗吗？我实在不明白阁下要怎么样匹配。
B1缓冲只有一级作为阻抗匹配非常好。

一孤

热帖呀，油翁的前级看来不简单

不会烧

好前级难觅。看卖油翁的帖子。以为我等穷烧有福了
可到最后还是为了卖东西做的铺垫
zhengjun30 发表于 2010-6-3 14:35

同感

ch639827608

A-30PreAmp的1Hz～200Hz线性和20Hz～20KHz线性也非常好，不过也是三级的。