<div dir="ltr">I'm comparing the data sheets, and I wonder that the
<span style="font-size:small;text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline">AD781<span> may be "too good" in some respects for synth use, and not good enough in others. It has an internal capacitor, unlike the
<span style="font-size:12.8px;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline">LF398<span> which uses an external one (that you can replace with different values/types to fit the app), Its sample rate is more than fast enough for audio, but the droop rate spec of 1uV/uS looks bad for sub-audio sampling (as in generating slow stepped control voltages) - I read that as one volt per second! Looking at online prices, it's also a lot more expensive than the Natio ... TI part, even considering that it's from Analog Devices.<br><br>Reading the LF198 datasheet reminds me of the "capacitor soakage" article(s) by Bob Pease. He even developed circuits to (somewhat) counteract the effect. If high precision and long hold time is needed, I think a two-stage circuit (small capacitor in the first, larger capacitor in the second) might be workable.<br></span></span></span></span><div><span style="font-size:12.8px"><br></span></div><div><span style="font-size:12.8px">For a synth module, I'd expect a S/H device to work well from as low as 50 uS sampling (of a 20kHz waveform) and as long as a minute hold time (a long sustained CV for a VCO), to cover all possible applications.</span></div><div><span style="font-size:12.8px"><br></span><span style="font-size:small;text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline"><span></span></span><div class="gmail_extra"><br><div class="gmail_quote">On Thu, Jun 7, 2018 at 5:49 PM, Tom Bugs <span dir="ltr"><<a href="mailto:admin@bugbrand.co.uk" target="_blank">admin@bugbrand.co.uk</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div text="#000000" bgcolor="#FFFFFF">
<p>If anyone would be interested in taking a stash of the similar
Analog Devices AD781 chip.. <br>
I probably have 20+ unused DIP + some working pulls.<br>
Happy to work something out if anyone is interested in making use
of them.</p>
<p>Tom<br>
</p><div><div class="h5">
<br>
<div class="m_-4762838971533870287moz-cite-prefix">On 07/06/2018 22:44, Tim Ressel wrote:<br>
</div>
<blockquote type="cite">
<p>Make sure to buffer the signal going in to the LF398. It will
not work well if driven with a soft source.</p>
<p>--timmers<br>
</p>
<br>
<div class="m_-4762838971533870287moz-cite-prefix">On 6/7/2018 9:21 AM, Elain Klopke
wrote:<br>
</div>
<blockquote type="cite">
<div dir="ltr">Hey all,
<div><br>
</div>
<div>In my poking around the internets for sample and hold
circuits, I ran across the Texas Instruments LF398
monolithic sample and hold. It looks promising, +/-5 to
+/-18V supply range, up to +/-18V input range, TTL and CMOS
compatable logic input, all in a DIP8 package.</div>
<div><br>
</div>
<div>Does anyone have any experience with this chip?</div>
</div>
<br>
<fieldset class="m_-4762838971533870287mimeAttachmentHeader"></fieldset>
<br>
<pre>______________________________<wbr>_________________
Synth-diy mailing list
<a class="m_-4762838971533870287moz-txt-link-abbreviated" href="mailto:Synth-diy@synth-diy.org" target="_blank">Synth-diy@synth-diy.org</a>
<a class="m_-4762838971533870287moz-txt-link-freetext" href="http://synth-diy.org/mailman/listinfo/synth-diy" target="_blank">http://synth-diy.org/mailman/<wbr>listinfo/synth-diy</a>
</pre>
</blockquote>
<br>
<pre class="m_-4762838971533870287moz-signature" cols="72">--
--Tim Ressel
Circuit Abbey
<a class="m_-4762838971533870287moz-txt-link-abbreviated" href="mailto:timr@circuitabbey.com" target="_blank">timr@circuitabbey.com</a></pre>
<br>
<fieldset class="m_-4762838971533870287mimeAttachmentHeader"></fieldset>
<br>
<pre>______________________________<wbr>_________________
Synth-diy mailing list
<a class="m_-4762838971533870287moz-txt-link-abbreviated" href="mailto:Synth-diy@synth-diy.org" target="_blank">Synth-diy@synth-diy.org</a>
<a class="m_-4762838971533870287moz-txt-link-freetext" href="http://synth-diy.org/mailman/listinfo/synth-diy" target="_blank">http://synth-diy.org/mailman/<wbr>listinfo/synth-diy</a>
</pre>
</blockquote>
<br>
</div></div><span class="HOEnZb"><font color="#888888"><pre class="m_-4762838971533870287moz-signature" cols="72">--
BugBrand LTD
UK company No. 07199808
VAT No. GB 988 2629 57
1 Ninetree Hill
BRISTOL BS1 3SB
United Kingdom
<a class="m_-4762838971533870287moz-txt-link-abbreviated" href="http://www.bugbrand.co.uk" target="_blank">www.bugbrand.co.uk</a></pre>
<div id="m_-4762838971533870287DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2"><br>
<table style="border-top:1px solid #d3d4de">
<tbody><tr>
<td style="width:55px;padding-top:13px"><a href="http://www.avg.com/email-signature?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=emailclient" target="_blank"><img alt="" width="46" height="29" style="width:46px;height:29px"></a></td>
<td style="width:470px;padding-top:12px;color:#41424e;font-size:13px;font-family:Arial,Helvetica,sans-serif;line-height:18px">Virus-free. <a href="http://www.avg.com/email-signature?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=emailclient" style="color:#4453ea" target="_blank">www.avg.com</a>
</td>
</tr>
</tbody></table><a href="#m_-4762838971533870287_DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2" width="1" height="1"> </a></div></font></span></div>
<br>______________________________<wbr>_________________<br>
Synth-diy mailing list<br>
<a href="mailto:Synth-diy@synth-diy.org">Synth-diy@synth-diy.org</a><br>
<a href="http://synth-diy.org/mailman/listinfo/synth-diy" rel="noreferrer" target="_blank">http://synth-diy.org/mailman/<wbr>listinfo/synth-diy</a><br>
<br></blockquote></div><br></div></div></div>