本帖最后由 无声游侠 于 2017-3-8 23:19 编辑
20170308
输出电阻与保护电路 输出电阻原设计是没有的,这样相对于DT880 600Ω之类的高阻抗耳机来说,这意味耳机放大器有着比较高的阻尼系数,在我的系统来说,接近2000?而加入输出电阻以后最直接的就是增加了放大器的输出阻抗,这意味着也影响了机器的输出功率还有阻尼系数,虽然阻尼系数对于机器来说虽然并不是一个重要的指标,但在于参考的意义还是聊胜于无吧。至于输出电阻的选择,有外国朋友已经做了详细的研究,在这里“借”来说明一下罢。
“What outputresistors does it have and which HP (impedance) do you want the numbers for.
The power levels are dependant of those 2 values.
Here are the powers for a Panda with a NO (0 Ohm) output resistor (rounded offvalues):
HP impedance ....Class-A......Class-AB
32 Ohm ..............640mW.......3,125mW
64 Ohm ..............1,280mW ...1,560mW
150 Ohm ............670mW ......670mW
300 Ohm ............330mW ......330mW
600 Ohm.............170mW ......170mW
Here are the powers for a Panda with a 10 Ohm output resistor (rounded offvalues):
HP impedance ....Class-A......Class-AB
32 Ohm ..............640mW.......1,800mW
64 Ohm ..............1,170mW ...1,170mW
150 Ohm ............580mW ......580mW
300 Ohm ............310mW ......310mW
600 Ohm.............170mW ......170mW
Here are the powers for a Panda with a 22 Ohm output resistor (rounded offvalues):
HP impedance ....Class-A......Class-AB
32 Ohm ..............640mW.......1,100mW
64 Ohm ..............640mW ......870mW
150 Ohm ............510mW ......510mW
300 Ohm ............290mW ......290mW
600 Ohm.............160mW ......160mW
Here are the powers for a Panda with a 47 Ohm output resistor (rounded offvalues):
HP impedance ....Class-A......Class-AB
32 Ohm ..............500mW.......500mW
64 Ohm ..............500mW ......500mW
150 Ohm ............380mW ......380mW
300 Ohm ............250mW ......250mW
600 Ohm.............140mW ......140mW
Here are the powers for a Panda with a 75 Ohm output resistor (rounded offvalues):
HP impedance ....Class-A......Class-AB
32 Ohm ..............280mW.......280mW
64 Ohm ..............330mW ......330mW
150 Ohm ............300mW ......300mW
300 Ohm ............210mW ......210mW
600 Ohm.............130mW ......130mW
Here are the powers for a Panda with a 120 Ohm output resistor (rounded off values):
HP impedance ....Class-A......Class-AB
32 Ohm ..............140mW.......140mW
64 Ohm ..............190mW ......190mW
150 Ohm ............200mW ......200mW
300 Ohm ............170mW ......170mW
600 Ohm.............120mW ......120mW
So pick your headphone impedance and you will have a pretty good idea.
NOTE: Most headphones can handle a power of around 100mW to 200mW.
You can clearly see that a higher output resistance of the amp leads to safervalues for all headphones where 0 Ohm or low Ohmic values can seriouslyoverdrive (destroy) low Ohmic headphones ! file:///Z:/temp/msoclip1/01/clip_image002.gif
High Ohmic headphones are always in the 'safe zone' with this amp.
Amps with a 120 Ohm output resistor in the output are also always in the 'safezone'.
Some headphones, however, perform sonically better at lower output resistancesbut you must be aware that these low output resistance values can destroy lowOhmic headphones.”
引用这位外国朋友的结论,大部份的耳放如果接上120Ω的输出电阻的话,耳机总会很安全,也可以节省一个保护电路。不过,这样子的做法对于声音有正面的影响吗,我看这只能算是一个折冲的选择。是不是真的需要一个输出电阻?如何做才是最佳的选择呢?放大器的输出阻抗当然是越小越好,一个10Ω~120Ω的电阻器相对于放大器内部以mΩ为单位的输出阻抗,都算得上巨大了;而对于熊猫耳放这样的深度负反馈类型的放大器,按照经验来讲,阻尼系数选值大致在50~2000之间;所以对于DT880 600Ω来说,如果一定要一个输出电阻的话,也许10Ω的电阻器会是一个比较好的选择。
至于保护电路,你真的需要放大器输出保护电路?对于我自己来说,虽然一开始就将保护部分的电路元件安装好了,但一直没有使用过,因为真的觉得不需要。另,保护电路的取样电容器C26,在取样电阻51K的情况下,100U的容量自然没问题,但好像选样有一点错误,取样电容器应当使用无极电容吧;再一个,继电器由于触点的存在,总还是会影响到机器的声音表现的。所以,保护电路的使用与否,这也是一个选择。
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