📄 preamp_line_2_eng.htm
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<title>Audio Line High-End Preamplifier with ICs</title>
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<td width="100%" bgcolor="#800000" height="25"><p align="center"><font face="Tahoma"
color="#FFFF00"><big><strong>Audio Line High-End Preamplifier with ICs</strong></big></font></td>
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<td width="100%" height="12"><strong><small><small><small><font face="Tahoma"><small><small><span
lang="EN-US"
style="font-size:12.0pt;font-family:
Tahoma;mso-fareast-font-family:"Times New Roman";mso-ansi-language:EN-US;
mso-fareast-language:EL;mso-bidi-language:AR-SA">Generally.</span></small></small></font></small></small></small></strong></td>
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<td width="100%" height="1"><font face="Tahoma"><span lang="EN-US"
style="font-size:12.0pt;font-family:
Tahoma;mso-fareast-font-family:"Times New Roman";mso-ansi-language:EN-US;
mso-fareast-language:EL;mso-bidi-language:AR-SA"><span
lang="EN-US" style="font-size:10.0pt;font-family:Tahoma;mso-ansi-language:EN-US">Afterwards
the Modular preamplifier presentation good is I present also a simpler circuit in the
manufacture but very good quality. And in this circuit the philosophy that follow is:
simple is also better. As you will see in the circuit, it was used only that a Volume
potentiometer. Even the Tape Monitor choice, is considered more enough seldom in the use,
remaining useful only in those who they allocate and insist to use 3 heads cassette
players and tape open reel. Otherwise can used also this input as LINE, after does not
differ in nothing from the other inputs or be suppressed. All the components that
constitute the circuit should be top quality. The preamplifier gave sound very good and
neutral.<span style="mso-spacerun: yes"> </span></span><span lang="EN-US"
style="font-size:10.0pt;mso-bidi-font-size:12.0pt;font-family:Tahoma;
mso-ansi-language:EN-US"><o:p></o:p></span></span></font></td>
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<td width="100%" height="983"><p align="center"><img
src="preamp_2a.gif" tppabs="http://users.otenet.gr/~athsam/Circuits/preamp_line_2/preamp_2a.gif" width="1001" height="1044"
alt="preamp_2a.gif (37806 bytes)"></td>
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<td width="100%" height="6"><b><span lang="EN-US"
style="font-size:10.0pt;font-family:
Tahoma;mso-fareast-font-family:"Times New Roman";mso-ansi-language:EN-US;
mso-fareast-language:EL;mso-bidi-language:AR-SA">Description</span></b></td>
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<td width="100%" height="4"><span lang="EN-US"
style="font-size:10.0pt;font-family:
Tahoma;mso-fareast-font-family:"Times New Roman";mso-ansi-language:EN-US;
mso-fareast-language:EL;mso-bidi-language:AR-SA"><font
face="Tahoma"><span lang="EN-US"
style="font-size:10.0pt;font-family:Tahoma;mso-ansi-language:EN-US">In the Fig.1A appears
the main body that concerns the sound. In the choice exist my constant preference in the
relay. I believe that it is the better solution, after it offers the better results of use
and sound quality and stability in the time. Of course it depends from the relay quality
that we will use. A lot of good constructors offer the suitable solutions. What it should
we are careful they are closed type and they contain in the packing diode parallel with
the inductor. If we select some type that does not allocate diode parallel with the
inductor then it will be supposed place diodes. All the circuit does not allocate unyoke
capacitor in the road of sound signal, following DC coupling [for this helps trimmers TR1
-6]. The acoustic signal from the input that be selected is directed in the first buffer
stage, that is constituted by two single opamp. IC1 -2. This stage does not offer gain in
the acoustic signal. As you would observe in the drawing, all the opamp. allocate one
small trimmer [TR1 until<span style="mso-spacerun: yes"> </span>TR6]. The use these
trimmers us allows the precise Offset voltage adjusting in the exit opamp. in very low
levels [200uV]. Whoever judges that this is excessive, it can them suppress. In each
trimmer they exist jumper switch SF1-4. Each switch selects if the trimmer it抯 supplied
by positive or negative voltage line. This depends from the opamp. type that will be used.
If we lead to concrete opamp. type and it will need we change then we can suppress. In
Table 1 appears the voltage polarity with which it should be connected the trimmer
depending on opamp. type. The regulation trimmer should become, after the preamplifier
works few time and with potentiometer RV1 in lowest resistance [closed], without it is
connected some power amplifier in the preamplifier output. The opamp. choices in places<span
style="mso-spacerun: yes"> </span>IC5 -6 are such in order that the trimmer
connection TR5 -6 becomes exclusively with the positive voltage line. Afterwards the first
stage it follows the RV1 VOLUME potentiometer, which should they are very good quality. It
follows the OUTPUT LINE stage constituted from the IC3 -4. In this stage becomes level
gain of such signal in level so that are drve all the types of power amplifiers. With
values R15 -18=15Kohm and R16 -20=2.2Kohm the gain is roughly 17dB [X7 5]. This gain can
change, if we change somebody from these resistances following the calculation type of
gain A = R14 + R15 + R16 / R16. Resistances R14-18 protect the opamp. exit from
short-circuit as also they make the suitable long cables adaptation. These resistances are
placed in the feedback bronchus, for this reason should they are calculated in the total
gain. In the output exist the contacts of RL6 that close when passes the delay time that
is determined by the C13 and IC7a-b [Fig 1A], so that are not listen annoying noises in
the power supply opening and the closure. Opamp.<span style="mso-spacerun: yes"> </span>IC5-6
they function as buffer with X1 gain, driving the Record outputs J11 -12.<span
style="mso-spacerun: yes"> </span><o:p></o:p></span></font></span></td>
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<td width="100%" colspan="2" bgcolor="#FFFF80"><p align="center"><font face="Tahoma"
color="#FF0000"><strong><small>Table 1</small></strong></font></td>
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<td width="50%" align="center" bgcolor="#FFFFBB"><strong><font face="Tahoma"><small>NE5534</small></font></strong></td>
<td width="50%" bgcolor="#FFFFD9"><small><strong><font face="Tahoma">+V</font></strong></small></td>
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<td width="50%" align="center" bgcolor="#FFFFBB"><small><font face="Tahoma"><strong>OPA604</strong></font></small></td>
<td width="50%" bgcolor="#FFFFD9"><small><strong><font face="Tahoma">-V</font></strong></small></td>
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<td width="50%" align="center" bgcolor="#FFFFBB"><small><font face="Tahoma"><strong>OPA627</strong></font></small></td>
<td width="50%" bgcolor="#FFFFD9"><small><strong><font face="Tahoma">+V</font></strong></small></td>
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<td width="50%" align="center" bgcolor="#FFFFBB"><small><font face="Tahoma"><strong>OPA637</strong></font></small></td>
<td width="50%" bgcolor="#FFFFD9"><small><strong><font face="Tahoma">+V</font></strong></small></td>
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<td width="100%" height="6"><b><span lang="EN-US"
style="font-size:10.0pt;font-family:
Tahoma;mso-fareast-font-family:"Times New Roman";mso-ansi-language:EN-US;
mso-fareast-language:EL;mso-bidi-language:AR-SA">Opamp.
Choice</span></b><span lang="EN-US"
style="font-size:10.0pt;font-family:Tahoma;mso-fareast-font-family:
"Times New Roman";mso-ansi-language:EN-US;mso-fareast-language:EL;mso-bidi-language:
AR-SA">.
</span></td>
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<td width="100%" height="4"><span lang="EN-US"
style="font-size:10.0pt;font-family:Tahoma;mso-fareast-font-family:
"Times New Roman";mso-ansi-language:EN-US;mso-fareast-language:EL;mso-bidi-language:
AR-SA"><font
face="Tahoma"><span lang="EN-US"
style="font-size:10.0pt;font-family:Tahoma;mso-ansi-language:EN-US">The opamp. choice is a
basic factor for the good reproduction of sound. A cheap, but good solution is the use in
all the places of classic NE5534. The better certain choice are the OPA604, OPA627 and
OPA637 of Burr - Brown but they are more expensive. The OPA637 is Top but it does not
provide stability with gain under X4, hence it is excluded from places IC1-2-5-6 where the
gain is X1. The OPA604 is the better choice because it has too much good characteristics
and is good-value. Is a single fast opamp. that combines use FET but also bipolar
technology semiconductors. It has very low distortion, low noise, big bandwidth, he is
constant in the gain X1 and it can drive 600 ohms loads.<span style="mso-spacerun: yes">
</span></span><b><span lang="EN-US"
style="font-size:
10.0pt;mso-bidi-font-size:12.0pt;font-family:Tahoma;mso-ansi-language:EN-US"><o:p></o:p></span></b></font></span></td>
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<td width="33%" bgcolor="#FFFF80"><p align="center"><font face="Tahoma" color="#FF0000"><small><strong>Part
List Main Preamp. [Fig.1A]</strong></small></font></td>
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