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<p>Maybe its time to breadboard the beastie? <br>
</p>
<br>
<div class="moz-cite-prefix">On 6/8/2018 2:46 PM, Ben Bradley wrote:<br>
</div>
<blockquote type="cite"
cite="mid:CA+wjhVuwZ17nHu=8=PJhPM2Qi=B_gUFmvFoMvHB+ehA2EEVv0w@mail.gmail.com">
<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"
moz-do-not-send="true">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>
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