Ok thanks for the info. I think I need to adjust my circuit a bit. I am maxing out at 15k using LM13700 and 50pF caps<span></span>. I get a better range with just a pot as a viltage divider and no expo conversion, so i am guessing my error is in the convertor. I am reading TH's book on the 3080 right now. I will redisgn the expo conversion based on what I am learning.<div><br></div><div>Thanks!</div><div><br></div><div><br></div><div>-Jacob Watters<br><br>On Sunday, 23 October 2016, David G Dixon <<a href="mailto:dixon@mail.ubc.ca">dixon@mail.ubc.ca</a>> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><u></u>
<div bgcolor="#ffffff" text="#000000">
<div dir="ltr" align="left"><span><font color="#0000ff" size="2" face="Arial">...yeah, but if the filter doesn't go high enough, then it
doesn't allow all the higher overtones when its fully open. In other
words, it doesn't fully open. This can change the sound of waveforms even
if it is above your hearing range by subtle modulation. I only hear up to
a little less than 13kHz myself. Too much loud rock
music.</font></span></div>
<div dir="ltr" align="left"><span><font color="#0000ff" size="2" face="Arial"></font></span> </div>
<div dir="ltr" align="left"><span><font color="#0000ff" size="2" face="Arial">In any case, I would recommend 220pF as a good size for filter
caps. It's always worked well for me. Of course, all my designs also
use the 2164 quad VCA chip for expo-controlled variable resistors, with the
standard 30k input resistor. This fixes the "baseline" frequency of my
filters at something like 21kHz.</font></span></div><br>
<blockquote style="BORDER-LEFT:#0000ff 2px solid;PADDING-LEFT:5px;MARGIN-LEFT:5px;MARGIN-RIGHT:0px" dir="ltr">
<div dir="ltr" lang="en-us" align="left">
<hr>
<font size="2" face="Tahoma"><b>From:</b> Synth-diy
[mailto:<a href="javascript:_e(%7B%7D,'cvml','synth-diy-bounces@dropmix.xs4all.nl');" target="_blank">synth-diy-bounces@<wbr>dropmix.xs4all.nl</a>] <b>On Behalf Of </b>Tim
Ressel<br><b>Sent:</b> Sunday, October 23, 2016 10:48 AM<br><b>To:</b>
<a href="javascript:_e(%7B%7D,'cvml','synth-diy@dropmix.xs4all.nl');" target="_blank">synth-diy@dropmix.xs4all.nl</a><br><b>Subject:</b> Re: [sdiy] Max Filter
Cutoff<br></font><br></div>
<div></div>
<p>Since most ears stop at 16KHz I'd say its safe to stop there.</p>
<p>--Tim (can't hear above 10K) Ressel<br></p><br>
<div>On 10/23/2016 9:47 AM, Jacob Watters
wrote:<br></div>
<blockquote type="cite">I am working on a filter and I was trying to get the maximum
cutoff up to 20kHz. I found that I needed much smaller caps than what
is usually used in most filters.
<div><br></div>
<div>Then I noticed that on the Arp 2600 the max filter cutoff is labelled
as 10kHz.</div>
<div><br></div>
<div>What is the normal max cutoff for a 4-pole -24dB analog
filter?</div><br>
<fieldset></fieldset> <br><pre>______________________________<wbr>_________________
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</pre></blockquote><br><pre cols="72">--
--Tim Ressel
Circuit Abbey
<a href="javascript:_e(%7B%7D,'cvml','timr@circuitabbey.com');" target="_blank">timr@circuitabbey.com</a></pre></blockquote></div>
</blockquote></div>