quad 405: error correction / current dumping amplifiers

millwood

I have seen quite a few posts about quad 405 and thought I would share with you my thoughts on it.

quad405 is unlike many of the amps we regularly see in that it is extordinary.

here is a schematic capture of one of the earlier quad 405.

on the first glance, it looks like an ordinary quasi complimentary power amp, with the two bdy77 as output devices.

but pay attention to the parts highlighted in yellow, especially the 120pf capacitor and the 3uh inductor, and how the output is wired.

Don't they look weird?


before we go on, here is a good site for all things quad405:

http://www.dc-daylight.ltd.uk/Va ... /QUAD-405-Mods.html

millwood

so what really is quad405?

well, the portion circled in red is actually the main amplifier. It runs off a lm301 and uses the upper dby77 as its output device.

the portion circled in green is called a current dumper (or anxulary amplifier) whose sole purpose is to correct the error in the main amplifier.

those parts circled in yellow are the error feedforward / feedback network.

millwood

the original quad405 is quite complicated, for a variety of reasons.

now, you can simplify it considerably.

here is an example.

A2 (ne5534) is the main amplifier.

the current dumper is that push/pull pair.

Please notice the equation in the note to how the errors will be fully corrected, when z1*z3=z2*z4.

You can use pretty much any opamp for A2. a normal opamp (ne5532/4, or even lf351) would work but obiviously their output power is limited because of low rail voltage.

if you use an opamp like lm3875, or opa541-549, you can get some very powerful amplifiers out of this design.

millwood

those designs are more or less for show.

what about a real one?

here is the schematic:

again, lt1022 is choosen because of simulation purposes.

R6 is a variable resistor.

the 2nd chart is the waveforms.

the red trace is the input.

the green trace is the output on the load.

the blue trace is the output at the opamp. Notice how distorted it is? But the output is almost a perfect sinewave.

millwood

you may ask that how the amp would do if we did use real transistors?

well, you want to make sure that the opamp doesn't run out of current.

one way to do that would be to use power opamps (lm3875, opa541, or tda2030) as the main amp.

another is to use darlingtons.

and here is the waveform.

millwood

here is a more modern version of the quad 405.

tjxy

只能看懂些电路，看不明白文字啊，有谁来翻译下

DIY浪子

好贴！！！赞

cencal

楼上的,翻译一下造福百姓那

tjxy

老外搞405搞出多个版本

DIY浪子

原帖由 millwood 于 2007-12-16 04:25 发表
quad 405: error correction / current dumping amplifiers

I have seen quite a few posts about quad 405 and thought I would share with you my thoughts on it.

quad405 is unlike many of the amps we regularly see in that it is extordinary.

here is a schematic capture of one of the earlier quad 405.

on the first glance, it looks like an ordinary quasi complimentary power amp, with the two bdy77 as output devices.

but pay attention to the parts highlighted in yellow, especially the 120pf capacitor and the 3uh inductor, and how the output is wired.

Don't they look weird?


before we go on, here is a good site for all things quad405:

http://www.dc-daylight.ltd.uk/Va ... /QUAD-405-Mods.ht

我外语不好　大家将旧看吧　呵呵～

QUAD 405　误差　修正　电流倾注放大器：
我看见了许多关于405的发帖，我想分享自己关于405的一些想法和心得。
QUAD405 实际并不是许多我们所通常所看到和理解的那样
这里有一份早期的Q405图纸
第一份扫描图纸看起来是一个由两个BDY77做为输出级的普通quasi complimentary 型放大器
请注意黄圈内的部分，特别是那个120PF电容和3UH　电感　以及输出级是古怪的
难道看起来不古怪吗？

在我们继续以前，请先看下面这个405　它是各个部分都很好的：
http://www.dc-daylight.ltd.uk/Va ... /QUAD-405-Mods.ht

原帖由 millwood 于 2007-12-16 04:27 发表
so what really is quad405?

well, the portion circled in red is actually the main amplifier. It runs off a lm301 and uses the upper dby77 as its output device.

the portion circled in green is called a current dumper (or anxulary amplifier) whose sole purpose is to correct the error in the main amplifier.

those parts circled in yellow are the error feedforward / feedback network.

那么什么才是对QUAD405正确的理解?

红色位置处的主要放大单元使得LM301和周边元件　提高了输出级DBY77的输出

而绿色部分是被称作　电流倾注　它的作用是修正　输入级工作后输出的错误（误差）

而部分是　错误（误差）的反馈网络

原帖由 millwood 于 2007-12-16 04:33 发表
the original quad405 is quite complicated, for a variety of reasons.

now, you can simplify it considerably.

here is an example.

A2 (ne5534) is the main amplifier.

the current dumper is that push/pull pair.

Please notice the equation in the note to how the errors will be fully corrected, when z1*z3=z2*z4.

You can use pretty much any opamp for A2. a normal opamp (ne5532/4, or even lf351) would work but obiviously their output power is limited because of low rail voltage.

if you use an opamp like lm3875, or opa541-549, you can get some very powerful amplifiers out of this design.

原版本的QUAD405 由于各种原因，看起来仿佛是非常复杂的

下面图纸是个简化的结构后的模型

A2 (ne5534) 是主放大单元

电流注入器是一个　推挽结构

请注意　当 z1*z3=z2*z4.这个等式成立的时候　这个错误（误差）将被完全修正
你可以使用　许多OP来替换A2 ,例如常见的(ne5532/4, or even lf351) 可以很好工作在低输出电压下
使用如 lm3875, or opa541-549,则可以得到大功率的输出

原帖由 millwood 于 2007-12-16 04:48 发表
those designs are more or less for show.

what about a real one?

here is the schematic:

again, lt1022 is choosen because of simulation purposes.

R6 is a variable resistor.

the 2nd chart is the waveforms.

the red trace is the input.

the green trace is the output on the load.

the blue trace is the output at the opamp. Notice how distorted it is? But the output is almost a perfect sinewave.

下面是一些类似的设计图纸
我再次选择了 lt1022 ，因为便于仿真

R6　是一个　可变电阻。
第二个图纸是信号波形
红色是输入
绿色是放大器输出
蓝色是OP的输出
请注意波形的变化
输出的正弦波形变得完美了

原帖由 millwood 于 2007-12-16 04:53 发表
you may ask that how the amp would do if we did use real transistors?

well, you want to make sure that the opamp doesn't run out of current.

one way to do that would be to use power opamps (lm3875, opa541, or tda2030) as the main amp.

another is to use darlingtons.

and here is the waveform.

你可能会问　如果我们使用真正的晶体管　放大器会成什么样？
OP 放大器会不会被用尽其输出电流

解决方式是
使用功率OP放大器　如 (lm3875, opa541, or tda2030) 做为主放大单元
或者输出级使用达林顿结构

下面是输出波形～

cencal

楼上继续

DIY浪子

翻译完毕　累死。。。如有错误　请斧正。。
谢谢millwood的精辟阐述和设计
我对Q405又有新的理解了　嘻嘻
Many thanks to you!

tjxy

学习

audioboy

hi.
I think in the original Quad405,LM301 is not a fast OP.
So,the 120pf capacitor  used here as the feedforward network.
the high frequency part of signal went stright into the current dumper(push/pull pair transisters).bypass the Tr3-Tr5,Tr7 transisters.

47ohm and 3uH，together with R5, as feedback（current parallel negative feedback ）.

so,the total gain is Io=A*Ii,current dump to the speaker.

ary

原帖由 millwood 于 2007-12-16 04:25 发表
I have seen quite a few posts about quad 405 and thought I would share with you my thoughts on it.

quad405 is unlike many of the amps we regularly see in that it is extordinary.

here is a s ...

你好,呵呵.

你引进来的好像是一张错的图

Look, 在你这张图上,保护电路部分,75R上的压降约0.45V,大概到了2A的负载电流,保护电路就会起作用.

而且，这里的2A是峰值！！！那实际上这个电路能发挥的功率是？？？

如果我没人估计错误，你这张图的电源电压应该是30-35V，是经发烧友改过的405的低压版本。

ary

原帖由 millwood 于 2007-12-16 04:27 发表
so what really is quad405?

well, the portion circled in red is actually the main amplifier. It runs off a lm301 and uses the upper dby77 as its output device.

the portion circled in green i ...

你好，你红色圈圈少圈了点东西：下面的40872和BDY77也是的，它与上面的BDY77组成乙类电流放大。

what do you think ?

ary

原帖由 millwood 于 2007-12-16 04:33 发表
the original quad405 is quite complicated, for a variety of reasons.

now, you can simplify it considerably.

here is an example.

A2 (ne5534) is the main amplifier.

the current dumper i ...

I think you must mean to say :" A2 (ne5534) is the main Voltage amplifier."

ary

原帖由 millwood 于 2007-12-16 04:48 发表
those designs are more or less for show.

what about a real one?

here is the schematic:

again, lt1022 is choosen because of simulation purposes.

R6 is a variable resistor.

the 2nd c ...

你好，你能告诉我在这张图里，你的“桥”平衡等式在哪么？

R2*R6 =？L1/C4 ？

另外，你可不可以把你设计的图纸的放大倍数算一下？谢谢。

ary

原帖由 millwood 于 2007-12-16 04:53 发表
you may ask that how the amp would do if we did use real transistors?

well, you want to make sure that the opamp doesn't run out of current.

one way to do that would be to use power opamps  ...

405电路中对OPAMP有电流输出能力有要求么？