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<DIV><FONT face=Arial size=2>nice tutorial. thanks!</FONT></DIV>
<DIV><FONT face=Arial size=2>I'm sure glad I asked here before getting the PCB
made. I thought that Exponential FM would have been more typical, thats why I
didn't add Linear FM. Yesterday was actually the first time I tried putting
something into the FM jacks on my synth. well, Before yesterday, I had
only 1 VCO. the Idea for this VCO is to be a simple, fit on a small PCB, and
take up little panel space. I have Oakley Sound VCOs for my main oscillators,
but I'd like to get this one to stay in tune with those.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>for the pots. I'm using 100K pots on a 100K load.
arg. I already spent a bunch of $ on those fancy spectrol 100k pots. I think
it'd be easier to just double the values of all the other resistors. I
think that would atleast reduce the warping enough and the 10K trimmer for V/Oct
would be more centered around what the value should actually be. I looked at
that java applet, It looks pretty nasty the way I have the circuit
now.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>about the coarse adjustment, I suppose +/-5 octaves
would be alot more useful. meant to change that.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>thanks !</FONT></DIV>
<DIV><FONT face=Arial size=2>ryan</FONT></DIV>
<DIV><BR></DIV>
<BLOCKQUOTE dir=ltr
style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px">I've
got a tutorial on pots at <A class=moz-txt-link-freetext
href="http://home.comcast.net/~sbernardi/elec/og2/partsub_pots.html">http://home.comcast.net/~sbernardi/elec/og2/partsub_pots.html</A>.
<BR>In general to avoid loading effects, you want your voltage divider pots to
be 5 to 10 times less than the resistance that loads them. So for a 100K input
resistor, use a 10K up to 50K pot. To see the effect of loading, I have a link
to Chris List's java applet that plots loading effects.<BR>You might want to
decrease R2 a bit to give yourself more Coarse freq adj range. As you have it,
you'll only get 6 octaves. Using a 300K will give you a 10 octave tuning
range.<BR>The FM input you have is feeding the exponential input - linear FM
is more typical. To get linear FM, move the end of R28 to pin 6 of U7B. Also,
you'll want to change the value of R28 to something above 1M.<BR>I would
also have a second 1v/octave input - duplicate the R27 input. I also
find having a front panel "LFO switch" useful. This would sum a large negative
voltage into your input summer, which would switch the frequency way down.
-15v through 300K into the summing amp with switch you down 5
octaves.<BR><BR>The 100pF compensates for the extra phase shift running
IC1A in the feedback loop of the opamp, and it is to prevent oscillation. I
also use 100pF because everybody else does.<BR></BLOCKQUOTE></BODY></HTML>