关于hood-1969功率管的选择

metaspark

最近看了一篇有关hood-1969 original circuit中对流行功率管的测试报告，希望对热衷于小甲的朋友有帮助。

原文如下：“The use of more modern ‘audio’ power transistors with a high current gain-bandwidth product (fT), such as the 2SC5200, 2SC3281 and MJL3281A, is not recommended at present. The >30MHz fT of these devices causes the open-loop gain to remain above unity when the phase shift through the amp reaches 180°. This results in instability and oscillation, which requires additional compensation such as a dominant pole capacitor. In a simple circuit such as this, the provision of a compensation capacitor can significantly increase distortion levels unless other circuit changes are made (which perhaps defeats the object of this simple design). However, I will be investigating various possible options for solving the instability problems since I would really like to try the highly linear MJL3281A device.

I have received feedback from one constructor, Tim Andrew, who has been trying alternative output transistors in his JLH 1996 version. The MJL3281A gave clearly audible oscillation. The MJ21194 gave a noticeable improvement in sound quality, but introduced a low frequency hum, the cause of which has yet to be determined. The MJ15003 gave a significant improvement in sound quality, similar to the MJ21194 but without the side effects. ”

大体的意思是目前用得比较广泛的大管如2SC5200, 2SC3281和MJL3281A，由于截至频率较高（>30MHz)，电路会出现振荡而不稳定，如果施加相位补偿，对于hood-1969这样简洁的电路又会造成较大的失真；fT与2N3055相近的MJ21194测试的结果也不够理想，低频有浑浊声。替代2N3055比较理想的管子是MJ15003（两管的fT相近）。另外其他测试结果表明MJ802也有不错表现。

题外：当然，音频功放制作不是只看参数指标，是否好声还要依个人听感为准，所以上面的测试结果只是提供一种参考。我看论坛有些朋友有些盲目追求高性能功率管，其实不是管子的性能参数越高就一定好，要看应用的电路结构。

metaspark

2# egame2001
我觉得可以参考下管子的datasheet，把静态电流设置在线性比较好的区域内，从2N3055的测试曲线看，0.1A~1A都还比较理想，MJ15003的datasheet中没有给出测试曲线，但从动态参数测试条件看也是选取静态电流0.5A比较理想。

xp6188

2# egame2001
我觉得可以参考下管子的datasheet，把静态电流设置在线性比较好的区域内，从2N3055的测试曲线看，0.1A~1A都还比较理想，MJ15003的datasheet中没有给出测试曲线，但从动态参数测试条件看也是选取静态 ...
metaspark 发表于 2010-8-10 09:14

如果设在线性好的0.5A是必输出功率过低，所以指标只能参考

li0532

甲类推挽加上负反馈，管子非线性失真的影响是很有限的。除非管子线性太差或上下臂不对称。

metaspark

5# xp6188
是的，所以参看国外不少线路后面使用多管并联分流输出，hood由于引入负反馈，非线性失真得以控制。

zyk601

请问：用三肯管3858好吗？

metaspark

8# zyk601
2SC3858没有使用过，看参数fT高达20MHz,这种高频管可能会存在与MJL3281同样的问题