<div>Hi All!! </div>
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<div>Today i rechecked all the pcb, connections, components values and found no error. I was about to give up when I decided to tweak some values on Rays circuit. I compared the VC RES section on both the SVF and the 4 pole LPF and noted there where very similar except for a value of a resistor connected to pin3 of the OTA. In the SVF it is 30k and in the 4pLFP is 200k. I dont know if this makes any sense but I replaced the 30k with a 200k and got a much better response of the RES pot. It oscillated near 3/4 of the rotation. Finally I put a 390k and now it oscillates near the end. Maybe I have a mistake in my board but this tweak really solved the problem. It sound really nice!!
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<div>Benjamín<br><br> </div>
<div><span class="gmail_quote">2006/3/21, Benjamín Velasco <<a href="mailto:guatis@gmail.com">guatis@gmail.com</a>>:</span>
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<div>Thanks Ray (and Roy) for your suggestions. I'll recheck the entire board tomorrow...now i'm a bit tired. Glad to hear that the filter should work fine under +-15V. I'll keep you informed. </div>
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<div>Greetings</div>
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<div>Benjamín<br> </div>
<div><span class="gmail_quote">2006/3/21, Ray Wilson <<a onclick="return top.js.OpenExtLink(window,event,this)" href="mailto:raywilson@comcast.net" target="_blank">raywilson@comcast.net</a>>:</span>
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<div><font face="Arial" size="2">It must be this one:</font></div><span>
<div><font face="Arial" size="2"></font> </div>
<div><font face="Arial" size="2"><a onclick="return top.js.OpenExtLink(window,event,this)" href="http://www.musicfromouterspace.com/analogsynth/STATEVARVCFFEB2006/STATEVARVCFFEB2006.html" target="_blank">http://www.musicfromouterspace.com/analogsynth/STATEVARVCFFEB2006/STATEVARVCFFEB2006.html
</a></font></div>
<div><font face="Arial" size="2"></font> </div></span>
<div><font face="Arial" size="2">Since its the only one that will oscillate.</font></div>
<div><font face="Arial" size="2"></font> </div>
<div><font face="Arial" size="2">It should not be acting the way you have described. You should only get oscillation near the end of the max resonance pot travel. Are you certain that all component values are correct especially those around the Res and COF pots. There are resistors in the circuit designed to limit the voltage range that the pots can deliver (COF R1, R5) and (RES R48, R52). If you need to adjust the range you can adjust them however when I tested this on +/-12V and +/-15V and I saw normal behavior. Also check the values around the VC resonance circuit. I'm not sure why you would be seeing what you've described under normal circumstances. Unsoldered component? Unsoldered off-board wire? Wrong value component?
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<div><font face="Arial" size="2"></font> </div>
<div><font face="Arial" size="2">Here are some troubleshooting suggestions:</font></div>
<div><font face="Arial" size="2"></font> </div>
<div><font face="Arial" size="2"><a onclick="return top.js.OpenExtLink(window,event,this)" href="http://www.musicfromouterspace.com/analogsynth/troubleshoot.html" target="_blank">http://www.musicfromouterspace.com/analogsynth/troubleshoot.html
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<div><font face="Arial" size="2"></font> </div>
<div><font face="Arial" size="2">Ray</font></div></div>
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<div style="FONT: 10pt arial">----- Original Message ----- </div>
<div style="BACKGROUND: #e4e4e4; FONT: 10pt arial"><b>From:</b> <a title="guatis@gmail.com" onclick="return top.js.OpenExtLink(window,event,this)" href="mailto:guatis@gmail.com" target="_blank">Benjamín Velasco</a> </div>
<div style="FONT: 10pt arial"><b>To:</b> <a title="synth-diy@dropmix.xs4all.nl" onclick="return top.js.OpenExtLink(window,event,this)" href="mailto:synth-diy@dropmix.xs4all.nl" target="_blank">Synth DIY List</a> </div>
<div style="FONT: 10pt arial"><b>Sent:</b> Tuesday, March 21, 2006 4:12 PM</div>
<div style="FONT: 10pt arial"><b>Subject:</b> [sdiy] Ray Wilson's SV VCF with +-15V</div>
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<div><span>Hi you all!! I recently finished this module from Ray's site using my +-15V PSU. I seems to work but the ranges of the pots are too extreme. It starts to oscillate as soon as I start moving the resonance pot, and also i cover the entire CutOff freq range near the center position of the COff pot. Can anybody help me figuring out what values to change so the response is like the +-12V version?. Or maybe it's simpler to use a couple of voltage regulators to get +-12V??. Thanks!!!
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