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<span>Hi all,<br>
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<div>I have never posted a question here but I have been subscribed for several years and I have learned a lot from reading the threads. Thank you all for this.
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<div>I am an sdiy hobbyist who enjoys making modules for my own use. I occasionally make music and I have played a few gigs out locally.<br>
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<div>I have recently finished my own version of the Thomas Henry 'Clangora'. I couldn't find NE566's (VCO's) so I just swapped them out for LM13700's and done the same with the NE571 (VCA's) while I was at it.<br>
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<div>I also added the XOR noise source and VCF's from Ken Stone's Cynare circuit.
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<div>It was looking like a huge module so I decided to not add CV control on version one. Now that it is finished I am really happy with how it sounds and I want to add CV control to the next version.<br>
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<div>I know how to stick in a OTA VCA here and there to add CV control to the Sweep and FM etc but I can't get my head around how to use an OTA to replace the variable resistors that are controlling the open and closed decay times.<br>
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<div>I know I could use a vactrol but these are pricey, bulky and slow etc so I'd rather not have to use them.
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<div>My guess after looking at the LM13700 datasheet would be that I need to use the 'floating vc resistor' configuration.<br>
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<div>I am no EE so I am totally patching bits of circuits from my Thomas Henry books together and hoping it sounds good :D<br>
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<div>Is it the 'floating VC resistor' configuration that I need to use in place of the open and closed decay resistors or is it something crazy complicated that's not in the datasheet?<br>
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<div><span style="font-family: Calibri, Helvetica, sans-serif; background-color: rgb(255, 255, 255); display: inline !important">Any advice on what I need to do here would be greatly appreciated.</span><br>
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<div><span style="font-family: Calibri, Helvetica, sans-serif; background-color: rgb(255, 255, 255); display: inline !important"><span style="font-family: Calibri, Helvetica, sans-serif; background-color: rgb(255, 255, 255); display: inline !important">Many
thanks in advance for any advice.</span><br>
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<div>Here's the trigger logic and envelope generator section of the original circuit which I downloaded in a PDF from Nuts&Volts (Nov2003):<br>
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<div>https://i.imgur.com/GXw9KVR.jpg<br>
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<div>My sketchy block diagram:<br>
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<div>https://i.imgur.com/absDij1.png<br>
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<div>A video of my first version of this module:<br>
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<div>https://youtu.be/mq05zgHSYso<br>
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<div>And my (slightly ridiculous) intended layout for the version two front panel:<br>
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<div>https://i.imgur.com/n0LzEoq.png<br>
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<div>My whole synth (last year):<br>
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<div>https://i.imgur.com/lcdscrw.jpg<br>
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<div>Best regards,<br>
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<div>Kevin Walsh.<br>
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