Classic FET input class A pre-stage

This circuit is a classic circuit supplemented by the circuit designed by Huang Xiaofeng, the first issue of the "Battery Powered Advanced Pure Class A Discrete Preamplifier" in the first issue of "Radio and Television" magazine 2000. It lists the specific parameters of R3, R4, R7, R10, R18, R19, and C2 that were not specified in the original circuit. This parameter was carefully calculated and carefully scrutinized by the teacher "Xinke". Because this line has the pure sweetness of pure nail single-ended, excellent sense of speed and transient response, it is especially shared with fans.


This pre-stage is actually a 20dB flat amplifier. Its main circuit is shown in Figure 1. It can be seen from the figure that it is a classic two-stage differential amplification and single-ended push DC circuit. Except for DCization measures, its voltage amplification and push-pull output stages work in the pure Class A state. Since the working point of the Class A amplification mobile phone is at the best load, the quiescent current value is half of the maximum current swing The push-pull tube works together, but the current of one tube increases and the current of the other tube decreases, so the response to the burst signal is extremely sensitive. Unlike some class AB or class B output currents, the input signal has a prolonged lag , There is no switching distortion and crossover distortion. In addition, the nonlinear distortion of the transistor's Ie-Vb can also be largely cancelled out, which minimizes the odd harmonic distortion that seriously harms the sweetness of the sound, although his efficiency is not high But it is a wise move to make the best use of it in the predecessor.
To obtain pure and low-noise playback, a particularly important foundation for high-quality power supplies. Foreign imported famous machines attach great importance to the quality of power supply.It can be seen that the quality of the power supply has a decisive influence on the quality of the whole machine. 6 6V / 1.5A, maintenance-free batteries of good quality, three positive and negative power supplies on each side. On the one hand, it lays a solid foundation for obtaining good sound quality, and on the other hand, it also omits the complicated design and the difficulty of making the power supply circuit. "Pre-stage circuit (power supply drawing)" is the charging circuit of the machine.
A good preamp should not only have good circuit design, good power supply, but also good component support, which is indispensable. Since there are not many components in this circuit, it will not be very difficult to use high-quality high-quality components. And the use of better components can also help to overcome the DC weakness of the machine, that is, the problem of DC zero drift, strict selection of transistors can largely guarantee that the output terminal maintains zero potential.
Since the input stage is at the forefront of the amplifier, it has very strict requirements on the noise of the whole machine. Generally, two-stage transistors are difficult to meet due to their low noise characteristics. In order to obtain better low-noise characteristics, the pre-stage uses high transconductance Gm junction field effect (JFET) composed of high impedance, large dynamic, low Noise differential amplifier, but the use of high transconductance FET tube also has its advantages and disadvantages, because the structure of the FET tube input capacitance and feedback capacitance is larger, so it has a certain modification of the tone. As for whether you like the warmth of gallbladder or the beauty of Shi Zhili, you will have different opinions. The input stage of this machine is using the common high-transconductance Gm junction field effect tube-NPD5564S on the market. Since this tube is a twin junction type tube, its internal characteristics are the same and no matching is required. Can save a lot of time. The use of junction field effect as the first stage of differential amplification also has an advantage, that is, when the operating current ID is large, it ensures a large dynamic range and a large transition current to charge R10 and C2. When using this tube as a differential input, The noise is still very small when the working power is large, and the quiescent current is 1.2mA.Under the premise of taking into account the signal-to-noise ratio, taking a larger apparent current not only improves the overload capacity of the stage, but also has the voltage conversion rate and bandwidth. The obvious improvement. When using ordinary bipolar transistors as the differential amplifier stage, the operating current is large, the current noise will inevitably increase sharply, and the human face will deteriorate the signal-to-noise ratio of the whole machine.
The dual-end output of the input stage makes the voltage amplification only form a differential amplifier, and the common mode rejection ratio of the two-stage differential amplifier makes the midpoint DC offset voltage drift of the machine very small. As shown in the figure, the load of the first stage, R10 And C2 are two-pole frequency compensation. BG2, BG3 form a common source common base circuit for BG1 to reduce the influence of the capacitance between the two poles of GB1, thus improving the high frequency response. In order to improve the common mode rejection ratio (CMRR ), A constant current source is shared, which is composed of BC4, D1, D2, B5 is the mirror current level, because the emitter resistance is about the same as the collector resistance, so the collector output waveform and the emitter waveform size The same, but in the opposite direction. The BG3 mirror current stage is used to add the BG3 output to the BG6 and BG4 output to the BG7 signal amplitude. Symmetrical single-ended push-pull output stage to obtain larger output current and lower output impedance.
The tube used in the second stage is Toshiba's C2240. The error of Hfe> 250 is best guaranteed within 3%. You can also use Vceo> 120V, Icm> 50mA, Pcm> 200, but pay attention to the consistency of the tube. Only in this way can we guarantee a better sound and better stability.
The last level is also not sloppy, the requirements of the tube parameters are Vceo> 160, Icm> 50mA, Pcm> 750mW, fT> 50MHz, there are many tubes on the market that meet the above requirements, including the well-known people who have established D756, B716 , D667, B647, and Toshiba's A1145, C2705, etc., this machine uses the familiar 2SB647, 2SD667, the requirements for the tube is Ic = 10mA pairing error is> 2%.
Finally, other components can't be very careless. The resistor is best to use Philips' five-color ring resistor. The power is 1 / 2W. The error should also be as small as possible. There are many choices in the capacitor market, but remember to use higher quality genuine products. The consistency of the capacitor and the rectifier capacitor cannot be ignored at the same time, because the different charging and discharging time of the positive and negative capacitors will make the power supply unbalanced, resulting in low-frequency self-excitation, the sound will deteriorate in the light, and the normal will be affected. jobs. Therefore, the capacitance error should be controlled within 3%. The potentiometer is ALPS plastic potentiometer. Other potentiometers can be selected from a potentiometer called COPALD that I have seen recently in the electrical appliance market. They are also plastic-sealed, and are sold in Japan at a price between 2-4 yuan. It is a gold pin, small in size, and high-quality transmission line is Teflon silver wire. It is also best to use silver-containing tin for soldering. The choice of the chassis depends on your own conditions, but you must pay attention to earthquake resistance.
The layout of the whole machine can be divided into three small chassis. The power supply on the left includes: transformer, charging circuit, the middle is the battery pack, and the right is the pre-stage circuit. The wiring should be short and not messy. It is best to shield sensitive traces .
In terms of debugging, as long as the component quality meets the requirements, the local debugging is not complicated. The voltage of the battery is first, and then the input terminal is short-circuited to the ground. Fine-tune W3 to make the output terminal 0V, and then adjust W2 to make the voltage difference between R9 and 5V. The final W4 makes the collector-to-ground voltage of BG5 and BG6 to -1V, wait for 30 minutes after completion, and then turn on the power to re-debug the above steps to make the output midpoint voltage 0V.

Technical area detailed analysis of Doherty power amplifier design load traction principle (top) detailed analysis of Doherty power amplifier design how to improve efficiency (lower) voltage follower input and output error analysis lm386 power amplifier energization will produce noise causes and treatment methods analysis class d Solve the effect of power amplifier on emi

Follow WeChat

Interesting and informative information and technical dry goods

Download Audiophile APP

Create your own personal electronic circle

Follow the audiophile class

Lock the latest course activities and technical live broadcast
Collect People collection
share it:
comment
Publish

related suggestion

var check_allow = "/d/Api/iscantalk.html"; var add_url = '/ d / article / write /'; function CheckLogin () {now_uid = ''; var ElecfansApi_checklogin = '/ webapi / passport / checklogin'; var logout_url = "{: U ('Login / logout')}"; var logout_url = 'http://bbs.elecfans.com/member.php?mod=logging&action=logout&refer=front'; $ .get (ElecfansApi_checklogin, function (data, textStatus) {if (data! = "") {EchoLoginInfo (data); CheckEmailInfo (data); data = $ .parseJSON (data); now_uid = data.uid; / * var login_content = 'write an article
'+ data.username +'
Quit '; * / var login_content =' write an article
'+ data.username +'
Set exit '; $ (' # login_area '). Html (login_content); var win_width = $ (window) .width (); if (win_width> 1000) {$ ("# mine"). MouseDelay (200) .hover (function () {$ ("# mymenu"). show ();}, function () {$ ("# mymenu"). hide ();});}} else {var content = 'Login Registration'; $ ('# login_area'). html (content); $ (". special-login"). click (function (e) {$ .tActivityLogin (); return false;});}});} $ (function () {// comment ------------------------------- var comment = $ ("# comment"); var comment_input = $ ("# comContent"); // Submit comment click event interaction $ ("# comSubmit2"). on ('click', function () {var content = comment_input.text (); // Empty input box comment_input. html (""). focus (); // Submit data to the server $ .ajax ({url: '/plus/arcComment.php', data: {aid: $ ("# webID"). val (), dopost : 'apiPubComment', content: content}, type: 'post', dataType: 'json', success: function (data) {// Data format returned: if (data.status == "successed") {// Build temporary comment DOM var dom = ''; dom + = '
'; dom + =' '; dom + ='
'; dom + ='

'+ data.data.username +' '; dom + ='

'; dom + =' '+ content +' '; dom + =' '; dom + =' just now '; dom + =' '; dom + =' '; // insert a temporary comment to the list $ ("# comment ") .append (dom);} if (data.status ==" failed ") {// alert (data.msg); layer.msg (data.msg);}}}); return false;}); (function () {/ * * Insert single sign-on JS * / var setHost = 'https://passport.elecfans.com'; // Set domain name var script = document.createElement ('script'); script.type = 'text / javascript'; script.src = setHost + '/public/pc/js/t.passport.js'; script.setAttribute ("id", "sso_script"); script.setAttribute ("data-ssoSite", setHost); script.setAttribute ("data-ssoReferer", encodeURIComponent (location.href)); script.setAttribute ("data-ssoSiteid", "11"); var body = document.getElementsByTagName ("body"). item ( 0); body.appendChild (script);}) () / * * It is recommended to modify the style of the article without a picture * * / $ (". Article .thumb"). Each (function () {if ($ (this). find ('img'). attr ('src') == "") {$ (this) .find ('img'). remove (); $ (this) .parent (). css ('padding-left ',' 0px ');}}); / * Baidu share * / window._bd_share_config = {common: {bdText: '', // Custom share content bdDesc: '', // Custom share summary bdUrl: window.location.href, // Custom share URL address bdPic: ''} , share: [{"bdSize": 60, "bdCustomStyle": true}]} with (document) 0 [(getElementsByTagName ('head') [0] || body) .appendChild (createElement ('script')). src = 'http://bdimg.share.baidu.com/static/api/js/share.js?cdnversion=' + ~ (-new Date () / 36e5)]; var add_url = '/ d / article / write / '; // var check_allow = "{: U (' Api / iscantalk ')}"; var check_allow = "/ d / api / iscantalk"; var click_items_length = $ ('. art_click_count '). length; if ( click_items_length> 0) {var id_str = ''; $ ('. art_click_count'). each (function () {id_str + = $ (this) .attr ('data-id') + ',';}) // var url = "{: U ('Api / getclickbyids')}"; var url = "/ d / api / getclickbyids"; var id_data = 'id_str =' + id_str; $ .ajax ({url: url, data: id_data, type: 'post', dataType: 'json', success: function (re) {if (re.list.length> = 1) {var list = re.list; for (var i in list) {var t emp_id = list [i] ['id']; var temp_span = $ (". art_click_count [data-id =" + temp_id + "]") temp_span.html (list [i] ['click']);}} }})} $ ("# comContent"). click (function () {if (now_uid == '') {$ .tActivityLogin (); return false;}}) $ (function () {var follow_wrap = $ ( ".author-collect"); var now_uid = "{$ _super ['uid']}"; var face_src = "{$ _super ['uface']}"; var getFollowNum = $ (". followNum strong"). html (); // Follow $ (window) .on ('click', '.author-collect', function () {if (now_uid == '') {$ .tActivityLogin (); return false;} if ( $ (this) .attr ('id') == 'follow') {$ .post ('/ d / user / follow', {tuid: article_user_id}, function (data) {// Data format returned: if (data.status == "successed") {$ (". followNum strong"). html (++ getFollowNum); follow_wrap.html ('followed'). attr ('id', 'cancelFollow'). css ( 'background', '# 999'); var follow_user = ' '; $ (' # follow_list '). append (follow_user);} if (data.status == "failed") {alert (data.msg);}});} else {// Unfollow if ($ ( this) .attr ('id') == 'cancelFollow') {$ .post ('/ d / user / cancelFollow', {tuid: article_user_id}, function (data) {// Data format returned: if (data .status == "successed") {follow_wrap.html ('Follow'). attr ('id', 'follow'). css ('background', '# f90'); $ (". followNum strong"). html (-getFollowNum); $ ('# follow_list .face'). each (function () {var target_uid = $ (this) .attr ('data-uid'); if (target_uid == now_uid) {$ ( this) .remove ();}})} if (data.status == "failed") {alert (data.msg);}}); return false;}}});});}); / * var myface = "{$ _super ['uid'] | avatar}"; var myname = "{$ _super ['username']}"; var article_id = {$ article ['id']}; var article_user_id = {$ article ['mid']}; // Article author ID $ (function () {<notempty name = "clearnum"> // Reduce the number of reminders var count = parseInt ($ ("# noticeCount"). html ()); count = count-{$ clearnum}; $ ("# noticeCount"). html (count); if ( count

Our Advantages:High refresh rate: With NOVA control system,no scanning line when photographed;High gray level: 256 RGB each, display 16.7M colors, vivid and perfect video effect;High resolution: The most apparent features of the new generation of LED Display;High Brightness: 6000-8000cd/m2, brightness automatically adjusted;High Quality: CE, RoHs, FCC, IP65, ISO9001 passed + 72 Hours serious testing time;Long life span: over100,000hours, warranty at least 2 years.           

You need = We design: Provide Personal- Customized led offer.

Price Advantage:We have the best competitive price at the market, also have the same even better quality

Quality advantage:From material to finished product, from design to produce, we control all steps,that's the guarantee of the quality and reliability.Better service at same situation, better cooperation at same service.



Billboard LED Display

Billboard Led Display,Advertising Led Display,Led Panel Billboard,Full Color Led Screen

Shenzhen Bako Vision Technology Co., Ltd. , http://www.rentalleddisplays.com