Pure Class-A = Headphone=20 Amplifier - RED

Single-rail Supply - Optional Tilt Control

=20

Circuit diagram:

Parts:

P1_____________22K  Dual gang Log Potentiometer (ready for Stereo)=0A=
=0A=
R1_____________15K  1/4W Resistor=0A=
R2____________220K  1/4W Resistor=0A=
R3____________100K  1/2W Trimmer Cermet=0A=
R4_____________33K  1/4W Resistor=0A=
R5_____________68K  1/4W Resistor=0A=
R6_____________50K  1/2W Trimmer Cermet=0A=
R7_____________10K  1/4W Resistor=0A=
R8,R9__________47K  1/4W Resistors=0A=
R10,R11_________2R2 1/4W Resistors=0A=
R12_____________4K7 1/4W Resistor=0A=
R13_____________4R7 1/2W Resistor=0A=
R14_____________1K2 1/4W Resistor=0A=
R15,R18_______330K  1/4W Resistors (Optional)=0A=
R16___________680K  1/4W Resistor (Optional)=0A=
R17,R19_______220K  1/4W Resistors (Optional)=0A=
R20,R21________22K  1/4W Resistors (Optional)=0A=
=0A=
C1,C2,C3,C4____10=B5F  25V Electrolytic Capacitors=0A=
C5,C7_________220=B5F  25V Electrolytic Capacitors=0A=
C6,C11________100nF  63V Polyester Capacitors=0A=
C8___________2200=B5F  25V Electrolytic Capacitor=0A=
C9,C12__________1nF  63V Polyester Capacitors (Optional)=0A=
C10___________470pF  63V Polystyrene or Ceramic Capacitor (Optional)=0A=
C13____________15nF  63V Polyester Capacitor (Optional)=0A=
=0A=
D1_____________5mm. or 3mm. LED=0A=
D2,D3________1N4002 100V 1A Diodes=0A=
=0A=
Q1,Q2_________BC550C  45V 100mA Low noise High gain NPN Transistors=0A=
Q3____________BC560C  45V 100mA Low noise High gain PNP Transistor=0A=
Q4____________BD136   45V 1.5A PNP Transistor=0A=
Q5____________BD135   45V 1.5A NPN Transistor=0A=
=0A=
IC1____________7815   15V 1A Positive voltage regulator IC=0A=
=0A=
T1_____________220V Primary, 15 + 15V Secondary (30V center-tapped)=0A=
                    5VA Mains transformer=0A=
=0A=
SW1____________4 poles 3 ways rotary Switch (ready for Stereo)=0A=
SW2____________SPST slide or toggle Switch=0A=
=0A=
J1_____________RCA audio input socket=0A=
J2_____________6mm. or 3mm. Stereo Jack socket=0A=
=0A=
PL1____________Male Mains plug=0A=

=20

Comments:

This design is derived from the Portable=20 Headphone Amplifier featuring an NPN/PNP compound pair emitter = follower=20 output stage. An improved output driving capability is gained by making = this a=20 push-pull Class-A arrangement. Output power can reach 427mW RMS into a = 32 Ohm=20 load at a fixed standing current of 100mA.
The single voltage gain = stage=20 allows the easy implementation of a shunt-feedback circuitry giving = excellent=20 frequency stability.

Tilt Control

The above mentioned shunt-feedback configuration also allows the = easy=20 addition of frequency dependent networks in order to obtain an useful,=20 unobtrusive, switchable Tilt control (optional).
When SW1 is set in = the first=20 position a gentle, shelving bass lift and treble cut is obtained. The = central=20 position of SW1 allows a flat frequency response, whereas the third = position of=20 this switch enables a shelving treble lift and bass cut. See the graph=20 below:

Notes:

Q4, Q5 and IC1 must be fitted with a small U-shaped heatsink.
For a Stereo version of this circuit, all parts must be doubled = except P1,=20 IC1, R14, D1, D2, D3, C8, T1, SW1, SW2, J2 and PL1.
If the Tilt Control is not needed, omit SW1, all resistors from = R15=20 onwards and all capacitors from C9 onwards. Connect the rightmost = terminal of=20 R1 to the Base of Q1.
Before setting quiescent current rotate the volume control P1 to = the=20 minimum, Trimmer R6 to zero resistance and Trimmer R3 to about the = middle of=20 its travel.
Connect a suitable headphone set or, better, a 33 Ohm 1/2W = resistor to the=20 amplifier output.
Connect a Multimeter, set to measure about 10Vdc fsd, across the = positive=20 end of C5 and the negative ground.
Switch on the supply and rotate R3 in order to read about 7.7-7.8V = on the=20 Multimeter display.
Switch off the supply, disconnect the Multimeter and reconnect it, = set to=20 measure at least 200mA fsd, in series to the positive supply of the=20 amplifier.
Switch on the supply and rotate R6 slowly until a reading of about = 100mA=20 is displayed.
Check again the voltage at the positive end of C5 and readjust R3 = if=20 necessary.
Wait about 15 minutes, watch if the current is varying and = readjust if=20 necessary.
Those lucky enough to reach an oscilloscope and a 1KHz sine wave=20 generator, can drive the amplifier to the maximum output power and = adjust R3=20 in order to obtain a symmetrical clipping of the sine wave = displayed.

Technical data:

Output power (1KHz sinewave):: 32 Ohm: 427mW RMS; 64 Ohm: 262mW RMS; 100 Ohm: 176mW RMS; 300 Ohm: 64mW RMS; 600 Ohm: 35mW RMS; 2000 Ohm: 10mW RMS
Sensitivity:: 140mV input for 1V RMS output into 32 Ohm load (31mW); 500mV input for 3.5V RMS output into 32 Ohm load (380mW)
Frequency response @ 2V RMS:: See the above graph
Total harmonic distortion into 32 Ohm load @ 1KHz:: 1V RMS 0.005% 3V = RMS 0.015%=20 3.65V RMS (onset of clipping) 0.018%
Total harmonic distortion into 32 Ohm load @ 10KHz:: 1V RMS 0.02% 3V = RMS 0.055%=20 3.65V RMS (onset of clipping) 0.1%
Unconditionally stable on capacitive loads

a?0:a},ea=3D/^([\w-]+\.)*([\w-]{2,})(\:[0-9]+)?$/,fa=3Df= unction(a,b){if(!a)return b;var c=3Da.match(ea);return c?c[0]:b};var = ga=3Dt("0.15"),ha=3Dt("0.01"),ia=3Dt("0.001"),ja=3Dt("0.0"),ka=3Dt("0.001= "),la=3Dt("0.2"),ma=3Dt("0.001");var = na=3D/^true$/.test("false")?!0:!1,oa=3D/^true$/.test("false")?!0:!1;var = qa=3D/&/g,ra=3D//g,ta=3D/"/g,ua=3D/'/g,u=3D{"\x00":"\\0","\b":= "\\b","\f":"\\f","\n":"\\n","\r":"\\r","\t":"\\t","\x0B":"\\x0B",'"':'\\"= ',"\\":"\\\\"},v=3D{"'":"\\'"};var x=3Dfunction(a){x[" "](a);return = a};x[" "]=3Dfunction(){};var = y=3Ddocument,B=3Dwindow,C,va=3Dnull,E=3Dy.getElementsByTagName("script");= E&&E.length&&(va=3DE[E.length-1]);C=3Dva;var G=3Dfunction(a,b){for(var c = in = a)Object.prototype.hasOwnProperty.call(a,c)&&b.call(null,a[c],c,a)},H=3Df= unction(a){return!!a&&"function"=3D=3Dtypeof = a&&!!a.call},wa=3Dfunction(a,b){if(!(2>arguments.length))for(var = c=3D1,e=3Darguments.length;cMath.random())){var = c=3DMath.random();if(c>2)+a.charCodeAt(e)&4294967295= ;return 0c;++c){var = e=3D9!=3Da.nodeType&&a.id,e=3De?"/"+e:"",d;o:{var = f=3Da.parentElement;d=3Da.nodeName.toLowerCase();if(f)for(var = f=3Df.childNodes,g=3D0,=0A= m=3D0;me;++e){for(var = d=3Dc.frames,f=3D0;fe;b=3Db.parentNode,++e)a.push(9!=3Db.nodeType&&b.id||"= ");(b=3Da.join())&&c.push(b)}else c.push(za(b)),c.push(Aa(a));return = N(c.join(":")).toString()},O=3Dfunction(a){try{return!!a.location.href||"= "=3D=3D=3Da.location.href}catch(b){return!1}};var = Ca=3D!!window.google_async_iframe_id,Da=3D/MSIE = [2-7]|PlayStation|Gecko\/20090226|Android 2\.|Opera/i,Ea=3D/Android/;var = P=3D!0,Fa=3D{},Ha=3Dfunction(a,b,c,e){var = d,f=3DP;try{d=3Dc()}catch(g){try{var = m,h=3Dg.toString();g.name&&-1=3D=3Dh.indexOf(g.name)&&(h+=3D": = "+g.name);g.message&&-1=3D=3Dh.indexOf(g.message)&&(h+=3D": = "+g.message);if(g.stack){var = k=3Dg.stack;c=3Dh;try{-1=3D=3Dk.indexOf(c)&&(k=3Dc+"\n"+k);for(var = p;k!=3Dp;)p=3Dk,k=3Dk.replace(/((https?:\/..*\/)[^\/:]*:\d+(?:.|\n)*)\2/,= "$1");h=3Dk.replace(/\n = */g,"\n")}catch(z){h=3Dc}}m=3Dh;h=3D"";g.fileName&&(h=3Dg.fileName);k=3D-= 1;g.lineNumber&&(k=3Dg.lineNumber);var D;o:{try{D=3De?e():"";break = o}catch(pa){}D=3D""}f=3D=0A= b(a,m,h,k,D)}catch(A){Ga({context:"protectAndRun",msg:A.toString()+"\n"+(= A.stack||"")})}if(!f)throw g;}return = d},Ja=3Dfunction(a,b,c,e,d,f){a=3D{context:a,msg:b.substring(0,512),eid:d= &&d.substring(0,40),file:c,line:e.toString(),url:y.URL.substring(0,512),r= ef:y.referrer.substring(0,512)};Ia(a);Ga(a,f);return = P},Ga=3Dfunction(a,b){if(Math.random()<(b||0.01)){var = c=3D"/pagead/gen_204?id=3Djserror"+Ka(a),c=3D"http"+("https:"=3D=3DB.loca= tion.protocol?"s":"")+"://pagead2.googlesyndication.com"+c,c=3Dc.substrin= g(0,2E3);B.google_image_requests||=0A= (B.google_image_requests=3D[]);var = e=3DB.document.createElement("img");e.src=3Dc;B.google_image_requests.pus= h(e)}},Ia=3Dfunction(a){var = b=3Da||{};G(Fa,function(a,e){b[e]=3DB[a]})},Q=3Dfunction(a,b){return = da(Ha,a,Ja,b,void 0)},Ka=3Dfunction(a){var = b=3D"";G(a,function(a,e){if(0=3D=3D=3Da||a)b+=3D"&"+e+"=3D"+("function"=3D= =3Dtypeof encodeURIComponent?encodeURIComponent(a):escape(a))});return = b};var R=3Dnull,La=3Dfunction(){if(!R){for(var = a=3Dwindow,b=3Da,c=3D0;a!=3Da.parent;)if(a=3Da.parent,c++,O(a))b=3Da;else= break;R=3Db}return R};var = S=3Dfunction(a,b,c){c||(c=3Doa?"https":"http");return[c,"://",a,b].join("= ")};var Ma=3Dfunction(){},Oa=3Dfunction(a,b,c){switch(typeof b){case = "string":Na(b,c);break;case = "number":c.push(isFinite(b)&&!isNaN(b)?b:"null");break;case = "boolean":c.push(b);break;case "undefined":c.push("null");break;case = "object":if(null=3D=3Db){c.push("null");break}if(b instanceof Array){var = e=3Db.length;c.push("[");for(var = d=3D"",f=3D0;fb?d+=3D"000":256>b?d+=3D"00":4096>b&&(d+= =3D"0");return Pa[a]=3Dd+b.toString(16)}));b.push('"')};var = T=3D"google_ad_block google_ad_channel google_ad_client google_ad_format = google_ad_height google_ad_host google_ad_host_channel = google_ad_host_tier_id google_ad_output google_ad_override = google_ad_region google_ad_section google_ad_slot google_ad_type = google_ad_unit_key google_ad_unit_key_2 google_ad_unit_key_3 = google_ad_unit_key_css google_ad_unit_key_dom google_ad_unit_key_var = google_ad_unit_key_win google_ad_width google_adtest = google_allow_expandable_ads google_alternate_ad_url = google_alternate_color google_analytics_domain_name = google_analytics_uacct google_bid google_captcha_token google_city = google_color_bg google_color_border google_color_line google_color_link = google_color_text google_color_url google_container_id = google_content_recommendation_ui_type google_contents google_country = google_cpm google_ctr_threshold google_cust_age google_cust_ch = google_cust_criteria google_cust_gender google_cust_id = google_cust_interests google_cust_job google_cust_l google_cust_lh = google_cust_u_url google_disable_video_autoplay google_ed google_eids = google_enable_content_recommendations google_enable_ose = google_enable_ose_periscope google_encoding google_floating_ad_position = google_font_face google_font_size google_frame_id google_gl google_hints = google_image_size google_kw google_kw_type google_lact google_language = google_loeid google_max_num_ads google_max_radlink_len google_mtl = google_num_radlinks google_num_radlinks_per_unit = google_only_ads_with_video google_only_pyv_ads = google_only_userchoice_ads google_override_format google_page_url = google_previous_watch google_previous_searches google_referrer_url = google_region google_reuse_colors google_rl_dest_url google_rl_filtering = google_rl_mode google_rt google_safe google_sc_id google_scs google_sui = google_skip google_tag_for_child_directed_treatment google_tag_info = google_targeting google_tdsma google_tfs google_tl google_ui_features = google_ui_version google_video_doc_id google_video_product_type = google_video_url_to_fetch google_with_pyv_ads google_yt_pt = google_yt_up".split(" "),=0A= Ra=3D{google_analytics_domain_name:!0,google_analytics_uacct:!0},Sa=3Dfun= ction(a){a.google_page_url&&(a.google_page_url=3DString(a.google_page_url= ));var b=3D[];G(a,function(a,e){if(null!=3Da){var d;try{var = f=3D[];Oa(new = Ma,a,f);d=3Df.join("")}catch(g){}d&&wa(b,e,"=3D",d,";")}});return = b.join("")};var = U=3Dfunction(a){this.b=3Da;a.google_iframe_oncopy||(a.google_iframe_oncop= y=3D{handlers:{},upd:n(this.o,this)});this.m=3Da.google_iframe_oncopy},Ta= ;var V=3D"var = i=3Dthis.id,s=3Dwindow.google_iframe_oncopy,H=3Ds&&s.handlers,h=3DH&&H[i]= ,w=3Dthis.contentWindow,d;try{d=3Dw.document}catch(e){}if(h&&d&&(!d.body|= |!d.body.firstChild)){if(h.call){setTimeout(h,0)}else = if(h.match){try{h=3Ds.upd(h,i)}catch(e){}w.location.replace(h)}}";=0A= /[&<>"']/.test(V)&&(-1!=3DV.indexOf("&")&&(V=3DV.replace(qa,"&")),-1!= =3DV.indexOf("<")&&(V=3DV.replace(ra,"<")),-1!=3DV.indexOf(">")&&(V=3D= V.replace(sa,">")),-1!=3DV.indexOf('"')&&(V=3DV.replace(ta,""")),= -1!=3DV.indexOf("'")&&(V=3DV.replace(ua,"'")));Ta=3DV;U.prototype.set= =3Dfunction(a,b){this.m.handlers[a]=3Db;this.b.addEventListener&&this.b.a= ddEventListener("load",n(this.n,this,a),!1)};=0A= U.prototype.n=3Dfunction(a){a=3Dthis.b.document.getElementById(a);try{var= = b=3Da.contentWindow.document;if(a.onload&&b&&(!b.body||!b.body.firstChild= ))a.onload()}catch(c){}};U.prototype.o=3Dfunction(a,b){var = c=3DUa("rx",a),e;o:{if(a&&(e=3Da.match("dt=3D([^&]+)"))&&2=3D=3De.length)= {e=3De[1];break o}e=3D""}e=3D(new = Date).getTime()-e;c=3Dc.replace(/&dtd=3D(\d+|M)/,"&dtd=3D"+(1E4>e?e+"":"M= "));this.set(b,c);return c};var Ua=3Dfunction(a,b){var c=3Dnew = RegExp("\\b"+a+"=3D(\\d+)"),e=3Dc.exec(b);e&&(b=3Db.replace(c,a+"=3D"+(+e= [1]+1||1)));return b};var W;o:{var Va=3Dl.navigator;if(Va){var = Wa=3DVa.userAgent;if(Wa){W=3DWa;break o}}W=3D""}var = X=3Dfunction(a){return-1!=3DW.indexOf(a)};var = Xa=3DX("Opera")||X("OPR"),Ya=3DX("Trident")||X("MSIE"),Za=3DX("Gecko")&&-= 1=3D=3DW.toLowerCase().indexOf("webkit")&&!(X("Trident")||X("MSIE")),$a=3D= -1!=3DW.toLowerCase().indexOf("webkit");(function(){var = a=3D"",b;if(Xa&&l.opera)return = a=3Dl.opera.version,"function"=3D=3Daa(a)?a():a;Za?b=3D/rv\:([^\);]+)(\)|= ;)/:Ya?b=3D/\b(?:MSIE|rv)[: = ]([^\);]+)(\)|;)/:$a&&(b=3D/WebKit\/(\S+)/);b&&(a=3D(a=3Db.exec(W))?a[1]:= "");return Ya&&(b=3D(b=3Dl.document)?b.documentMode:void = 0,b>parseFloat(a))?String(b):a})();var = ab=3Dnull,bb=3Dfunction(a){a=3Da||B.top;try{var = b=3Da.frames.google_esf;if(b&&O(b))return = b}catch(c){}try{for(b=3D0;b"].join("")},lb=3Dfunction(a,b,= c,e){return function(){var d=3D!1;e&&gb().al(3E4);var = f=3Da.document.getElementById(b);=0A= f&&!O(f.contentWindow)&&3=3D=3Da.google_top_js_status&&(a.google_top_js_s= tatus=3D6);try{if(O(a.document.getElementById(b).contentWindow)){var = g=3Da.document.getElementById(b).contentWindow,m=3Dg.document;m.body&&m.b= ody.firstChild||(m.open(),g.google_async_iframe_close=3D!0,m.write(c))}el= se{var = h=3Da.document.getElementById(b).contentWindow,k;f=3Dc;f=3DString(f);if(f= .quote)k=3Df.quote();else{g=3D['"'];for(m=3D0;mz)F=3Dp;else{var r=3D=0A= p;if(r in v)F=3Dv[r];else if(r in u)F=3Dv[r]=3Du[r];else{var = q=3Dr,w=3Dr.charCodeAt(0);if(31w)q=3Dr;else{if(256>w){if(q=3D"\\x= ",16>w||256w&&(q+=3D"0");q+=3Dw.toString(16).toUpperCase()}F=3Dv[r]=3D= q}}A=3DF}D[pa]=3DA}g.push('"');k=3Dg.join("")}h.location.replace("javascr= ipt:"+k)}d=3D!0}catch(vb){h=3DLa().google_jobrunner,fb(h)&&h.rl()}d&&(d=3D= Ua("google_async_rrc",c),(new = U(a)).set(b,lb(a,b,d,!1)))}},mb=3Dfunction(a){var = b=3D["");=0A= return b.join("")},nb=3Dfunction(a,b,c,e){e=3De?'"':"";var = d=3De+"0"+e;a.width=3De+b+e;a.height=3De+c+e;a.frameborder=3Dd;a.marginwi= dth=3Dd;a.marginheight=3Dd;a.vspace=3Dd;a.hspace=3Dd;a.allowtransparency=3D= e+"true"+e;a.scrolling=3De+"no"+e},ob=3Dfunction(a,b,c){var = e=3Db.google_ad_output,d=3Db.google_ad_format;d||"html"!=3De&&null!=3De||= (d=3Db.google_ad_width+"x"+b.google_ad_height,c&&(d+=3D"_as"));c=3D!b.goo= gle_ad_slot||b.google_override_format||!jb[b.google_ad_width+"x"+b.google= _ad_height]&&"aa"=3D=3Db.google_loader_used;d=3Dd&&c?d.toLowerCase():=0A= "";b.google_ad_format=3Dd;b.google_ad_unit_key=3DBa(null,C.parentElement,= b,!0);d=3Da.google_adk2_experiment=3Da.google_adk2_experiment||L(["C","E"= ],ka)||"N";"E"=3D=3Dd?(b.google_ad_unit_key_2=3DBa(a,C,b),d=3D[b.google_a= d_slot,b.google_ad_type],b.google_ad_unit_key_var=3DN(d.join()),a=3DAa(a)= ,d.push(a),b.google_ad_unit_key_win=3DN(a),a=3Dza(C),d.push(a),b.google_a= d_unit_key_dom=3DN(a),b.google_ad_unit_key_3=3DN(d.join(":"))):"C"=3D=3Dd= &&(b.google_ad_unit_key_2=3D"ctrl")},pb=3DMath.floor(1E6*Math.random()),q= b=3Dfunction(a){for(var b=3Da.data.split("\n"),=0A= c=3D{},e=3D0;e");h=3D"border:none;height:"+p+"px= ;margin:0;padding:0;position:relative;visibility:visible;width:"+k+"px;ba= ckground-color:transparent";b.write(['',c.join(" = "),""].join(""));h=3Dd.id;d=3Df.google_override_format||!jb[f= .google_ad_width+=0A= "x"+f.google_ad_height]&&"aa"=3D=3Df.google_loader_used?L(["c","e"],la):n= ull;ob(a,f,"e"=3D=3Dd);f=3DSa(f);if(b=3D1=3D=3Da.google_unique_id)ab||(ab= =3Dbb()),b=3D!ab;b?(b=3D{},nb(b,0,0,!1),b.style=3D"display:none",b.id=3D"= google_esf",b.name=3D"google_esf",c=3DS(fa("","googleads.g.doubleclick.ne= t"),"/pagead/html/r20140415/r20140417/zrt_lookup.html"),b.src=3Dc,b=3Dmb(= b)):b=3Dnull;c=3D(new Date).getTime();var = k=3Da.google_top_experiment,p=3Da.google_async_for_oa_experiment,=0A= z=3Da.google_always_use_delayed_impressions_experiment,g=3D["",b,"<",g,">",f,"google_show_ads_impl=3Dtrue;google_uniq= ue_id=3D",a.google_unique_id,';google_async_iframe_id=3D"',h,'";google_st= art_time=3D',s,";",k?'google_top_experiment=3D"'+k+'";':"",p?'google_asyn= c_for_oa_experiment=3D"'+p+'";':"",z?'google_always_use_delayed_impressio= ns_experiment=3D"'+z+'";':"",d?'google_append_as_for_format_override=3D"'= +d+'";':"","google_bpp=3D",c>s?c-s:1,";google_async_rrc=3D0;",kb(= ),""].join("");=0A= (a.document.getElementById(h)?hb:ib)(lb(a,h,g,!0))}});})();=0A= ------=_NextPart_000_0000_01CF5D7C.2CECD480--

Pure Class-A Headphone Amplifier

400mW RMS into 32 Ohm load