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<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Hi</span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>I am with Paul on this one. You need a
very stable reference voltage for the VCO core and for the frequency adjustment
pots. The more stable these voltages the better the VCO will be. Forget onboard
LM type regulator chips, even the 723. These can drift 1mV in a few seconds. Use
a precision voltage reference chip (0.6ppm) and buffer with some low drift Op
Amps. If you can’t get to the core (SSM/CEM chips) then precision
regulator the whole VCO power supply …This really works.</span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'> </span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Regards<br>
Rob</span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><a href="http://www.emulatorarchive.com/">www.emulatorarchive.com</a></span></font></p>
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style='font-size:12.0pt'> </span></font></p>
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<p class=MsoNormal style='margin-left:.5in'><font size=2 face=Arial><span
style='font-size:10.0pt;font-family:Arial'>b) you are trying to get cleaner
*power* to the VCO. This is not what the post is about. Rather, in a VCO
design, there will be a *reference voltage* (usually +5V) that either the
integration cap is tied to, or that the exponential current pair is referenced
to. There are many stable +5V reference chips to choose from, based on
price/performance.</span></font></p>
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style='font-size:12.0pt'> </span></font></p>
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<p class=MsoNormal style='margin-left:.5in'><font size=2 face=Arial><span
style='font-size:10.0pt;font-family:Arial'>Paul S.</span></font></p>
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style='font-size:12.0pt'> </span></font></p>
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<blockquote style='border:none;border-left:solid black 1.5pt;padding:0in 0in 0in 4.0pt;
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<p class=MsoNormal style='margin-left:.5in'><font size=2 face=Arial><span
style='font-size:10.0pt;font-family:Arial'>----- Original Message ----- </span></font></p>
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<div style='font-color:black'>
<p class=MsoNormal style='margin-left:.5in;background:#E4E4E4'><b><font size=2
face=Arial><span style='font-size:10.0pt;font-family:Arial;font-weight:bold'>From:</span></font></b><font
size=2 face=Arial><span style='font-size:10.0pt;font-family:Arial'> <a
href="mailto:guatis@gmail.com" title="guatis@gmail.com">Benjamín Velasco</a> </span></font></p>
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<p class=MsoNormal style='margin-left:.5in'><b><font size=2 face=Arial><span
style='font-size:10.0pt;font-family:Arial;font-weight:bold'>To:</span></font></b><font
size=2 face=Arial><span style='font-size:10.0pt;font-family:Arial'> <a
href="mailto:synth-diy@dropmix.xs4all.nl" title="synth-diy@dropmix.xs4all.nl">Synth
DIY List</a> </span></font></p>
</div>
<div>
<p class=MsoNormal style='margin-left:.5in'><b><font size=2 face=Arial><span
style='font-size:10.0pt;font-family:Arial;font-weight:bold'>Sent:</span></font></b><font
size=2 face=Arial><span style='font-size:10.0pt;font-family:Arial'> Monday,
April 10, 2006 12:00 PM</span></font></p>
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<p class=MsoNormal style='margin-left:.5in'><b><font size=2 face=Arial><span
style='font-size:10.0pt;font-family:Arial;font-weight:bold'>Subject:</span></font></b><font
size=2 face=Arial><span style='font-size:10.0pt;font-family:Arial'> [sdiy] Voltage
references in VCO</span></font></p>
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style='font-size:12.0pt'> </span></font></p>
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<p class=MsoNormal style='margin-left:.5in'><font size=3 face="Times New Roman"><span
style='font-size:12.0pt'>Hi list!!</span></font></p>
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<p class=MsoNormal style='margin-left:.5in'><font size=3 face="Times New Roman"><span
style='font-size:12.0pt'> A few days ago i started a topic about my LFOs
affecting the frequency of my VCOs. Searching the archives i discovered
this a very common problem. Someone here suggested to use on board voltage
references in the VCO rather than using massive decouple in all the other
modules. This makes sense to me because in my synth the only modules that need
critically good supply voltages are the VCOs. So i plan to use lm317/337 in
each of my VCOs. My question is if it is better to connect only the critical
points of the VCOs to the on board refences, or it is enough to use them for
the whole module? I use +-15V. Can i use the lm317/337 to get a cleaner
+-15V from the dirty +-15V or do I need higher voltage at the inputs of the
regulators?? </span></font></p>
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