<div dir="ltr">Oh boy, I'm gonna breadboard this! Thanks Dave :)<br></div><div class="gmail_extra"><br><div class="gmail_quote">On Mon, May 8, 2017 at 11:22 PM, David G Dixon <span dir="ltr"><<a href="mailto:dixon@mail.ubc.ca" target="_blank">dixon@mail.ubc.ca</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><u></u>
<div style="WORD-WRAP:break-word">
<div dir="ltr" align="left"><span class="m_-2223816546397876983088021704-09052017"><font face="Arial" size="2" color="#0000ff">Yes, that's right. Linear CV control has no temperature
effect.</font></span></div>
<div dir="ltr" align="left"><span class="m_-2223816546397876983088021704-09052017"><font face="Arial" size="2" color="#0000ff"></font></span> </div>
<div dir="ltr" align="left"><span class="m_-2223816546397876983088021704-09052017"><font face="Arial" size="2" color="#0000ff">Here's an interesting thing. A simple potentiometer is a
linear voltage selecting device. However, the current ratios of the two
sides of a pot are exponential. Hence, one can generate the proper
voltages for Hz/V control by putting a potentiometer on an opamp, with the wiper
going to the inverting input, one tap going to the output, and the other tap
going to the input. If a constant voltage is supplied to the input (say
0.8V), then linear movement of the pot will give exponential voltages at the
output of the opamp.</font></span></div>
<div dir="ltr" align="left"><span class="m_-2223816546397876983088021704-09052017"><font face="Arial" size="2" color="#0000ff"></font></span> </div>
<div dir="ltr" align="left"><span class="m_-2223816546397876983088021704-09052017"><font face="Arial" size="2" color="#0000ff">If the potentiometer is replaced with a bunch of equivalent
resistors connected in a chain, and a keyboard is used to connect the various
junction points to the inverting input of the opamp, then provided that there is
a trimmer on the input end of the resistor chain, this would give the proper
voltages for chromatic tuning (to be converted to currents to the integrator
directly) at the output of the opamp. Is that more or less the standard
approach?</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" class="m_-2223816546397876983OutlookMessageHeader" lang="en-us" align="left">
<hr>
<font face="Tahoma" size="2"><b>From:</b> Synth-diy
[mailto:<a href="mailto:synth-diy-bounces@synth-diy.org" target="_blank">synth-diy-bounces@<wbr>synth-diy.org</a>] <b>On Behalf Of </b>Adam
Inglis<br><b>Sent:</b> Monday, May 08, 2017 7:30 PM<br><b>To:</b>
<a href="mailto:synth-diy@synth-diy.org" target="_blank">synth-diy@synth-diy.org</a> DIY<br><b>Subject:</b> Re: [sdiy] MS-20 tempco (was
Model D service)<br></font><br></div><div><div class="h5">
<div></div>Hz - per - volt synths don’t need tempcos, do they?
<div><br></div>
<div>I have no experience with the MS-20 but I do have a Korg 700 from a few
years earlier. It never needs re-tuning.</div>
<div><br></div>
<div><br>
<div>
<blockquote type="cite">
<div>On 9 May 2017, at 11:53 AM, matt holland <<a href="mailto:matt@mattholland.org" target="_blank">matt@mattholland.org</a>>
wrote:</div><br class="m_-2223816546397876983Apple-interchange-newline">
<div>
<div dir="ltr">ebers moll equation: Ic = Is*e^(Vbe/Vt -1)
<div><br></div>
<div>a single transistor itself is an exponential converter. the second
transistor in the common two transistor expo converter compensates for the
complicated temperature dependance hidden in the Is term (Is goes away to
the extent that the two transistors are identical). the tempco resistor
compensates for the less severe effect of the temperature dependance hidden
in the Vt term. gory details of the equation terms can be found in your
nearest device physics textbook.</div>
<div><br></div>
<div><br></div></div>
<div class="gmail_extra"><br>
<div class="gmail_quote">On Mon, May 8, 2017 at 5:36 PM, Tony K <span dir="ltr"><<a href="mailto:weplar@gmail.com" target="_blank">weplar@gmail.com</a>></span> wrote:<br>
<blockquote style="BORDER-LEFT:#ccc 1px solid;MARGIN:0px 0px 0px 0.8ex;PADDING-LEFT:1ex" class="gmail_quote">Hello, those so-called special Rx's are 0.1% or
precision resistors , the ones with the circle around the resistor
symbol.<br><br>When we recorded I always had to tweak the Master Tune as
time went on. I never bothered adding one either. In mono synths it's not
critical , the exponential pair handles the biggest part of the temp drift
- forget the equation offhand.<br><br> Just referring to my notes ,
it's been a while.<br><span class="m_-2223816546397876983HOEnZb"><font color="#888888"><br>TK<br></font></span>
<div class="m_-2223816546397876983HOEnZb">
<div class="m_-2223816546397876983h5"><br>> On May 8, 2017, at 7:48 PM, Declare Update <<a href="mailto:declareupdate@gmail.com" target="_blank">declareupdate@gmail.com</a>>
wrote:<br>><br>> wait a second... no tempcos in the MS-20? what's
with all the special resistor symbols in the schematic? and how does that
super common and known-to-be-temp-dependent expo converter not need
compensation?<br>><br>> Chris<br>><br>>> On May 7, 2017, at
4:14 PM, Michael E Caloroso <<a href="mailto:mec.forumreader@gmail.com" target="_blank">mec.forumreader@gmail.com</a>>
wrote:<br>>><br>>> That's the one...<br>>><br>>>
MC<br>>><br>>>> Anyway, I think Michael E C was referring
to this posting of his:<br>>>> <a href="http://search.retrosynth.com/ah/search/lookit.cgi?-v9901.2166" rel="noreferrer" target="_blank">http://search.retrosynth.com/a<wbr>h/search/lookit.cgi?-v9901.216<wbr>6</a><br>>><br>>><br>>>>>
On 5/7/17, Michael Zacherl <<a href="mailto:sdiy-mz01@blauwurf.info" target="_blank">sdiy-mz01@blauwurf.info</a>>
wrote:<br>>>>><br>>>>>> On 7.May 2017, at 19:48
, Michael Zacherl <<a href="mailto:sdiy-mz01@blauwurf.info" target="_blank">sdiy-mz01@blauwurf.info</a>>
wrote:<br>>>>>><br>>>>>> On 7.May 2017, at
19:04 , Quincas Moreira <<a href="mailto:quincas@gmail.com" target="_blank">quincas@gmail.com</a>>
wrote:<br>>>>>><br>>>>>> Michael, thanks for
saving me frustration, I will refer to your<br>>>>>>
instructions.<br>>>>><br>>>>> uhm .. I didn’t do
anything -<br>>>><br>>>><br>>>> whoops
*blushes* … the other Michael.<br>>>><br>>>> Anyway, I
think Michael E C was referring to this posting of his:<br>>>> <a href="http://search.retrosynth.com/ah/search/lookit.cgi?-v9901.2166" rel="noreferrer" target="_blank">http://search.retrosynth.com/a<wbr>h/search/lookit.cgi?-v9901.216<wbr>6</a><br>>>><br>>>>
sorry, Michael E C,
Michael.<br>>>><br>>>><br>>>>
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<br></blockquote></div><br><br clear="all"><br>-- <br><div class="gmail_signature" data-smartmail="gmail_signature">Quincas Moreira<br>Test Pilot at VBrazil Modular</div>
</div>