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Check E&MM Spectrum synth sync solution, the timing cap can be shorted to either 1.6V or 3.85V (15V supply)</div>
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<a href="http://www.bigbluewave.co.uk/images/spectrum-notes-04.pdf">http://www.bigbluewave.co.uk/images/spectrum-notes-04.pdf</a><br>
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vco schematic on page 10</div>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>Lähettäjä:</b> Synth-diy <synth-diy-bounces@synth-diy.org> käyttäjän Finlay Shakespeare <futureimage@hotmail.co.uk> puolesta<br>
<b>Lähetetty:</b> tiistai 21. tammikuuta 2020 16.48<br>
<b>Vastaanottaja:</b> Neil Johnson <neil.johnson71@gmail.com><br>
<b>Kopio:</b> Synth DIY <synth-diy@synth-diy.org><br>
<b>Aihe:</b> Re: [sdiy] 3340 FET sync</font>
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Hi Neil,</div>
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D'oh! That makes total sense and, of course, makes it work perfectly. Now to hack a decent enough reference into the current prototype.</div>
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Thanks everyone!</div>
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<div id="x_Signature">Cheers!<br>
Fin<br>
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<div id="x_divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" color="#000000" style="font-size:11pt"><b>From:</b> Neil Johnson <neil.johnson71@gmail.com><br>
<b>Sent:</b> 21 January 2020 15:49<br>
<b>To:</b> Finlay Shakespeare <futureimage@hotmail.co.uk><br>
<b>Cc:</b> Synth DIY <synth-diy@synth-diy.org>; Oakley Sound <oakleysound@btinternet.com><br>
<b>Subject:</b> Re: [sdiy] 3340 FET sync</font>
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<div class="x_PlainText">Hi Finlay,<br>
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> The behaviour that I'm seeing from the 3340 is close to how Tony describes.<br>
> The triangle waveform at pin 10 is exactly as described in the datasheet, but the "triangle" across the timing cap at pin 11 is bang on +2V to +6V...<br>
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Ok, so in that case you CANNOT short the capacitor to 0V as you are<br>
currently doing. For this to work you need to recreate the lower<br>
internal threshold voltage and short the capacitor to that, not 0V.<br>
<br>
Neil<br>
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