JLH1969 MOSFET Class A/AB amp

qjdj

谢谢楼主提供的好电路，简单，好声。
是的，声音非常生动，空间感好，高音延展也很好，而且干净没有任何吵耳的感觉。
我手上还有nap140和仿金嗓子还有老乡liangsheng的小甲。这个电路是我第一次组成完整放大器准备长时间听的电路。

qjdj

顺便帖上我在diyaudio上参考的pcb版本。我是用洞洞版参考这个做的。很简单，pcb设计得也很好。

qjdj

顶给有兴趣的朋友看，很好声音的简单功放。

djm

原帖由 qjdj 于 2008-4-10 15:07 发表
顶给有兴趣的朋友看，很好声音的简单功放。

不错~~正想找个小甲~`

发烧龙

看完了,也想搭个试试.

阿伟

此为之精华帖，就请版主译成中文来！

qjdj

确定、一定已经肯定应该搭这个电路。听了2周了，还是依旧喜欢。翻老碟子重新感受中。
提供我在不同供电电压下的电阻取值。电压放大级，从上到下。42v：800欧、220欧、220欧
20v（是用的笔记本开关电源）：180欧、220欧、300欧。

jswzy

原帖由 qjdj 于 2008-4-21 15:12 发表
确定、一定已经肯定应该搭这个电路。听了2周了，还是依旧喜欢。翻老碟子重新感受中。
提供我在不同供电电压下的电阻取值。电压放大级，从上到下。42v：800欧、220欧、220欧
20v（是用的笔记本开关电 ...

看糊涂下,请问所搭的最终版本的电路图?

millwood

原帖由 jswzy 于 2008-4-21 22:38 发表

看糊涂下,请问所搭的最终版本的电路图?

here is one that probably works.

R11/R10 is replaced with a 10K (or 1K) pot. this pot determines the output voltage.

R9 determines the the input impedance. anything from 4.7k to 47k will work. a higher value resistor makes the amp suspect to interference and a lower value resistor here makes the amp hard to drive.

C6, together with R11/R10, determines the turn-on thump. anything from 1u to 4.7u will work. but can be as high as 110u. a larger capacitor here causes longer turn-on thump but minimizes power supply hum.

R3 determines Q1's idle current, and is "optional". I like to run my input stage at about 1ma each. depending on your transistors, you can run it hoter or cooler. the value of R3 can be from 1.1K (4ma idle current for Q1) to 10k (.4ma idle current for Q1). as designed, the input transistor runs at 1ma. a higher value R3 reduces thermal noise in the input transistor.

R5/R4 determines the gain (~10x in this case). C2 is the DC blocking cap.

R1 is a 1k (or 2k, if you intend to run the amp at higher voltage) pot. it controls the idle current in the mosfets.

R14 / R2 should be in the 110ohm to 470ohm range. R2 determines Q3's idle current and should be between 110ohm (30ma idle current for Q3) - 470ohm (8ma idle current for Q3). As designed, Q3 idles at about 15ma. the idle current of Q3 is determined by what kind of mosfets you drive. for larger power mosfet (IRFP140 or IRF540 for example), their gate capacitance is typically 2200pf - 3300pf. and at 20khz their gate current is about 1ma. you want Q3's idle current to be at least 10x of that.

R7/R13 are the gate stoppers. They are sized, again, based on the gate capacitance of the output devices, and are typically in the 47ohm - 470ohm range. for mosfets with higher gate capacitance, you want to use a bigger gate stopper but a bigger gate stopper limits bandwidth of the amp. I typically use a gate stopper in the 220 - 330ohm range and try to reduce it from there.

R8 / R12 are RE (or RS) resistors, for improved thermal stability. they can be from 0.1ohm - 1ohm.

C5 is an optional bulk capacitor. 22uf - 110uf will be good and you can parallel it with a 0.01uf - 0.1uf tantalum or polyester cap.

Q1: any small signal PNP transistor. it can either BJT or a P-channel small signal mosfet. if you use a p-channel mosfet, put in that 1k resistor (in green) to its gate.

Q3: any medium power NPN transistor (or N-channel mosfet). MJE1503x would be a good choice, as is IRF510 (my favorite) or FQA1n60 from fairchild (another of my favorite).

M3/M4: any power mosfets. like IRF540 (good for anything less than 20w) or IRfP140 for bigger amps.

the amp is typically quite stable and does not require a miller capacitor or a zobel network but having a zobel network is a good idle in general.

adjustment procedures:

a) once you finish soldering the amp, short the input. connect the ground to your power supply, and connect the positive rail to your power supply via a large power resistor (22ohm 10w for example).
b) adjust R10/R11 to set the middle point voltage to be roughly 1/2 of power supply. Adjust R1 so that the amp drops about 10mv on R8/R12 (idling at about 40ma).
c) short the power resistor so your amp sees full supply voltage. adjust R1 again so that the amp drops about 25mv on R8/R12 (idling at about 100 - 120ma).

by adjusting R1, you can easily control the idle current, and make the amp from Class A to Class AB easily. what I have found is that idling the amp at 100ma gives pretty good sound quality and idling it above 150ma does not give any improvement in sound quality. right now, I am running mine at 75ma (or 15mv voltage drop on R8/R12).

Hope it helps.

millwood

here are some simulation results.

a) waveform, for an amp that idles at 75ma.

green trace: output waveform;
blue trace: output current from the upper mosfet;
red trace: output current from the lower mosfet.

as you can see, the amp is working in class AB and idles at about 75ma.

millwood

here is the frequency response: flat to 1mhz, give or take a few.

in reality, it can reproduce wave forms higher than 100khz easily.

millwood

here is the waveform for 100khz pulses.

qjdj

原帖由 jswzy 于 2008-4-21 22:38 发表

看糊涂下,请问所搭的最终版本的电路图?

我是用的这个版本的图纸。

提供我在不同供电电压下的电阻取值。电压放大级，从上到下。42v：800欧、220欧、220欧
20v（是用的笔记本开关电源）：180欧、220欧、300欧。
就是指图中按顺序：R9   R8    R3

qjdj

感谢楼主继续提供帮助。
如果使用的音箱阻抗是4欧的，输出电容可以加到4700uf。低频更好，另外，图中2个220uf电容我也像楼主一样改成了470uf

millwood

the amp can be set-up to run at lower voltage: you just need to adjust R1 down accordingly.

yes, it runs on 4ohm or 2ohm load no problem.

it also runs stable with no difference is you parrellel a 2uf capacitor to the 4ohm load - very few amps can do that as youwill see sparks coming off the leads when you do that.

qjdj's schematic is essentially the same.

again, the amp is quite happy with pretty much any devices and reproduces sounds beautifully.

he121

原帖由 qjdj 于 2008-4-22 22:11 发表

我是用的这个版本的图纸。

提供我在不同供电电压下的电阻取值。电压放大级，从上到下。42v：800欧、220欧、 ...

双电源的OTL???有点不明白.这线路用卡版的PCB可以搭.

qjdj

不是双电源，你看“millwood”是为了仿真方便，其实负电源取的0v

jswzy

请问:
IRFP140可以用哪些管代,IRFP140

qjdj

这是最完整的图片。我用的这个电路。输入有22k对地电阻，可以稳定输入阻抗，因为我是声卡推动，推力强。

我是用的IRF640，很便宜的管子。

jswzy

原帖由 qjdj 于 2008-4-22 22:39 发表
这是最完整的图片。我用的这个电路。输入有22k对地电阻，可以稳定输入阻抗，因为我是声卡推动，推力强。
401245
我是用的IRF640，很便宜的管子。

谢谢!!!