📄 power_amplifier_65w_hexfet_eng.htm
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<title>Power amplifier 65W with HEXFET </title>
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<td width="100%" bgcolor="#800000"><p align="center"><em><font color="#FFFF00"
face="Arial"><strong>Power amplifier 65W with HEXFET</strong></font></em></td>
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<td width="100%"><p align="center"><img
src="power_amp_65w_a.gif" tppabs="http://users.otenet.gr/~athsam/Circuits/Power_amp_hexfet_65W/power_amp_65w_a.gif" width="794" height="547"
alt="power amp 65w hexfet [circuit]"></td>
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<td width="100%"><font face="Tahoma" size="2"><p align="justify"> </font><font
color="#800000" face="Tahoma" size="2">A medium power amplifier that is
characterized by a lot of good sound quality, but simultaneously is very simple in the
construction. Him uses, enough time in my active loudspeakers. In his output stage exist
the very good FET transistors, technology HEXFET, transistor which are controlled by
voltage and no by current as the classically bipolar transistors. The circuit has
symmetrical designing, resolving thus the harmonic distortion problem. All the transistors
that are used in the circuit are simple and they exist in big clearings in the market. The
pairs of differential amplifiers Q1-2 and Q3-4 should be matched between them and near the
one in the other. Thus you can buy enough transistors of types BC550C and BC560C, and with
a multimeter you match between them creating pairs with same characteristics, ensuring
thus uniform behavior in the temperature changes etc. Networks RC from the R7/C3 and
R12/C4 decrease the bandwidth of differential amplifiers and power amplifier in the
6.5MHZ. Resistors R8-9-10-11 function as local feedback in the differential amplifiers
improving the linearity. The differential amplifiers are supplied with constant current
from him current sources Q5 and Q6. The bias of current sources becomes from the
combination of diodes LED D1, D2 and R20. This becomes because the combination
transistor/LED ensures big thermic stability, for this reason should they are in very near
distance</font><font face="Verdana"><small><small><small><font color="#800000"> </font><font
color="#FF0000">[1]</font></small></small></small></font><font face="Tahoma" size="2"
color="#800000">. With the TR1 trimmer we regulate the bias current of output power stage.
For this reason Q8 should find itself on the heatsink so that it ensures thermic stability
in the bias, so that it does not change with the temperature changes. The resistors R32-33
shape a local feedback bronchus in the output stage, because this functions as voltage
amplifier. With the TR1, R3-4, C14 we regulate the amplifier output DC offset voltage,
near in the zero. The transistors Q8-10-11-12-13, [<strong>Fig.1</strong>] should
are placed on heatsink, adding between the transistors and the heatsink of good quality
leaves mica and ointment. Inductor L1 is constituted by 6 coils of insulated cupreous wire
of diameter 1.5mm, with internal inductor diameter of 16mm</font><font face="Verdana"
color="#ff0000"><small><small><small> [2]</small></small></small></font><font
face="Tahoma" size="2">. </p>
<p align="justify"></font><font face="Verdana" color="#800000" size="2"><u><b>Adjustment</b></u></font><font
face="Tahoma" size="2"></p>
<p align="justify"> <font color="#800000">Previous to we supply the amplifier with
voltage, we regulate the trimmer TR2 in the mid of his way and the trimmer TR1 in biggest
resistance. We connect a multimeter in output pin J4 (measurement range 200mV DC), we give
voltage in the amplifier and with the TR2 we regulate so that we take DC voltage in the
output as possible near in the zero. We remove the supply and connect a multimeter (range
1A or 2A) in line with one from the supply cables. We again give supply in the amplifier
and with the TR1 regulate late the current, so that we take clue roughly 330mA. We leave
the amplifier to work for 10 min., without audio signal in his input. Afterwards the
10-min. usually the current stabilized in 230mA roughly. If it needs we adjust late so
that we take clue near in 230mA. We again check the amplifier DC offset [J4] output, for
changes DC and if it needs we regulate again with the TR2. [Elektor12/93]. </font></font></p>
<ul>
<li><p ALIGN="JUSTIFY"><a href="protection_1.htm" tppabs="http://users.otenet.gr/~athsam/protection_1.htm"><small><font face="Verdana"
color="#0000FF"><strong>DC Protection / Time Delay for Loudspeaker</strong></font></small></a></p>
</li>
</ul>
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<td width="33%" bgcolor="#FFFF80"><p align="center"><font face="Arial" color="#800000"><small><strong>Part
List</strong></small></font></td>
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<td width="33%" bgcolor="#FFF4EA"><small><font face="Verdana"><strong>R1</strong>-15-16-21-22-17-18=1K<small>ohm</small></font></small></td>
<td width="33%" bgcolor="#FFF4EA"><small><font face="Verdana">R33=68<small>ohm</small> 5W</font></small></td>
<td width="34%" bgcolor="#FFF4EA"><small><font face="Verdana"><strong>Q1</strong>-2=<a
href="database.htm" tppabs="http://users.otenet.gr/~athsam/database.htm"><strong>BC550C</strong></a> [matched]</font></small></td>
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<td width="33%" bgcolor="#FFF4EA"><small><font face="Verdana">R2=47K<small>ohm</small></font></small></td>
<td width="33%" bgcolor="#FFF4EA"><small><font face="Verdana">R35-36=6.8<small>ohm</small>
1W</font></small></td>
<td width="34%" bgcolor="#FFF4EA"><small><font face="Verdana">Q3-4=<a href="database.htm" tppabs="http://users.otenet.gr/~athsam/database.htm"><strong>BC560C</strong></a>
[matched]</font></small></td>
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<td width="33%" bgcolor="#FFF4EA"><small><font face="Verdana">R3-4=10M<small>ohm</small></font></small></td>
<td width="33%" bgcolor="#FFF4EA"><small><font face="Verdana"><strong>TR1</strong>=1K<small>ohm</small>
trimmer</font></small></td>
<td width="34%" bgcolor="#FFF4EA"><small><font face="Verdana">Q5=<strong>BC560C</strong></font></small></td>
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<td width="33%" bgcolor="#FFF4EA"><small><font face="Verdana">R5-6-13-14=1.2K<small>ohm</small></font></small></td>
<td width="33%" bgcolor="#FFF4EA"><small><font face="Verdana">TR2=1M<small>ohm</small>
trimmer </font></small></td>
<td width="34%" bgcolor="#FFF4EA"><small><font face="Verdana">Q6=<strong>BC550C</strong></font></small></td>
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<td width="33%" bgcolor="#FFF4EA"><small><font face="Verdana">R7-12=47<small>ohm</small></font></small></td>
<td width="33%" bgcolor="#FFF4EA"><small><font face="Verdana"><strong>C1</strong>=2.2uF
63-100V MKT</font></small></td>
<td width="34%" bgcolor="#FFF4EA"><small><font face="Verdana">Q7-11=<a href="database.htm" tppabs="http://users.otenet.gr/~athsam/database.htm"><strong>BD140</strong></a></font></small></td>
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<td width="33%" bgcolor="#FFF4EA"><small><font face="Verdana">R8-9-10-11=22<small>ohm</small></font></small></td>
<td width="33%" bgcolor="#FFF4EA"><small><font face="Verdana">C2=1nF 100V MKT</font></small></td>
<td width="34%" bgcolor="#FFF4EA"><small><font face="Verdana">Q8-9-10=<strong><a
href="database.htm" tppabs="http://users.otenet.gr/~athsam/database.htm">BD139</a></strong></font></small></td>
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<td width="33%" bgcolor="#FFF4EA"><small><font face="Verdana">R19=82<small>ohm</small></font></small></td>
<td width="33%" bgcolor="#FFF4EA"><small><font face="Verdana">C3-4=2.7nF 100V MKT</font></small></td>
<td width="34%" bgcolor="#FFF4EA"><small><font face="Verdana">Q12=<a href="database.htm" tppabs="http://users.otenet.gr/~athsam/database.htm"><strong>IRF9540</strong></a></font></small></td>
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<td width="33%" bgcolor="#FFF4EA"><small><font face="Verdana">R20=22K<small>ohm</small></font></small></td>
<td width="33%" bgcolor="#FFF4EA"><small><font face="Verdana">C5=330pF ceramic or mylar</font></small></td>
<td width="34%" bgcolor="#FFF4EA"><small><font face="Verdana">Q13=<a href="database.htm" tppabs="http://users.otenet.gr/~athsam/database.htm"><strong>IRF540</strong></a></font></small></td>
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<td width="33%" bgcolor="#FFF4EA"><small><font face="Verdana">R23-26=56<small>ohm</small></font></small></td>
<td width="33%" bgcolor="#FFF4EA"><small><font face="Verdana">C6-7=100uF 16V</font></small></td>
<td width="34%" bgcolor="#FFF4EA"><small><font face="Verdana"><strong>F1</strong>-2=Fuse
2.5A Fast</font></small></td>
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<td width="33%" bgcolor="#FFF4EA"><small><font face="Verdana">R24=2.2K<small>ohm</small></font></small></td>
<td width="33%" bgcolor="#FFF4EA"><small><font face="Verdana">C8=1uF 100V MKT</font></small></td>
<td width="34%" bgcolor="#FFF4EA"><font face="Verdana"><small><strong>L1</strong>=see text
<small><font color="#FF0000"><small>[2]</small></font></small></small></font></td>
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<td width="33%" bgcolor="#FFF4EA"><small><font face="Verdana">R25=560<small>ohm</small></font></small></td>
<td width="33%" bgcolor="#FFF4EA"><small><font face="Verdana">C9-11-12=100nF 100V MKT</font></small></td>
<td width="34%" bgcolor="#FFF4EA"><small><font face="Verdana"><strong>J1</strong>= 2pin
connector 2.54mm step</font></small></td>
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<td width="33%" bgcolor="#FFF4EA"><small><font face="Verdana">R27-30=150<small>ohm</small></font></small></td>
<td width="33%" bgcolor="#FFF4EA"><small><font face="Verdana">C10-13=470uF 63V</font></small></td>
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<td width="33%" bgcolor="#FFF4EA"><small><font face="Verdana">R28-29-31-34=15<small>ohm</small></font></small></td>
<td width="33%" bgcolor="#FFF4EA"><small><font face="Verdana">C14=33nF 100V MKT </font></small></td>
<td width="34%" bgcolor="#FFF4EA"><small><font face="Verdana">Q8-10-11-12-13 on Heatsink</font></small></td>
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<td width="33%" bgcolor="#FFF4EA"><small><font face="Verdana">R32=150<small>ohm</small> 5W</font></small></td>
<td width="33%" bgcolor="#FFF4EA"><small><font face="Verdana"><strong>D1</strong>-2=LED
RED 3mm <small>[see text]<font color="#FF0000"><small> [1]</small></font></small></font></small></td>
<td width="34%" bgcolor="#FFF4EA"><small><small><font face="Verdana">All the resistors is
1/4W 1%</font></small> <small><font face="Verdana">except quote differently </font></small></small></td>
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<td width="33%"><p align="center"><font color="#FFFFFF">.</font></td>
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<td width="33%" bgcolor="#FFFF00"><p align="center"><font color="#800000"><strong>SPECIFICATIONS</strong></font></td>
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<td width="32%" bgcolor="#FFFFCC"><strong><small><font face="Verdana">POWER RATING</font></small>
<small><font face="Verdana">at 1KHZ with 0.1% THD</font></small></strong></td>
<td width="29%" bgcolor="#FFFFCC" align="center"><small><font face="Verdana">63W/ 8 ohm,
105W /4 ohm</font></small></td>
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<td width="32%" bgcolor="#FFFFCC"><strong><small><font face="Verdana">IMD</font></small></strong></td>
<td width="29%" bgcolor="#FFFFCC" align="center"><small><font face="Verdana"><0.008%</font></small></td>
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<td width="32%" bgcolor="#FFFFCC"><strong><small><font face="Verdana">THD at 60W into 8
ohm and 1 KHZ</font></small></strong></td>
<td width="29%" bgcolor="#FFFFCC" align="center"><small><font face="Verdana"><0.005%</font></small></td>
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