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<DIV dir=ltr align=left><SPAN class=788465906-09052017><FONT color=#0000ff
size=2 face=Arial>Sorry, I was wrong. It won't actually work. Don't
bother breadboarding it (or only do so to confirm that it's
wrong).</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=788465906-09052017><FONT color=#0000ff
size=2 face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=788465906-09052017><FONT color=#0000ff
size=2 face=Arial>If you make the following chain of resistors:
24k--1k--1k--1k--1k--1k--1k--1k--1k--1k--1k--1k--1k--36k (that's 24k,
then a dozen 1k's, then 36k, for a total resistance of 72k) and put
-1V into the 24k resistor and connect the 36k resistor to the opamp output, then
switch the inverting input to each of the resistor junctions, you will get the
following voltages:</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=788465906-09052017><FONT color=#0000ff
size=2 face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=788465906-09052017><FONT color=#0000ff
size=2 face=Arial>1.000 -- 1.057 -- 1.118 -- 1.182 -- 1.250 -- 1.323 -- 1.400 --
1.483 -- 1.571 -- 1.667 -- 1.769 -- 1.880 -- 2.000</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=788465906-09052017><FONT color=#0000ff
size=2 face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=788465906-09052017><FONT color=#0000ff
size=2 face=Arial>Here are the voltages you actually need:</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=788465906-09052017><FONT color=#0000ff
size=2 face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=788465906-09052017><FONT color=#0000ff
size=2 face=Arial>1.000 -- 1.059 -- 1.122 -- 1.189 -- 1.260 -- 1.335 -- 1.414 --
1.498 -- 1.587 -- 1.682 -- 1.782 -- 1.888 -- 2.000</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=788465906-09052017><FONT color=#0000ff
size=2 face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=788465906-09052017><FONT color=#0000ff
size=2 face=Arial>Here are the errors (all the voltages are too
small):</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=788465906-09052017><FONT color=#0000ff
size=2 face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=788465906-09052017><FONT color=#0000ff
size=2 face=Arial>0.000 -- 0.002 -- 0.004 -- 0.007 -- 0.010 -- 0.012 -- 0.014 --
0.015 -- 0.016 -- 0.015 -- 0.013 -- 0.008 -- 0.000</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=788465906-09052017><FONT color=#0000ff
size=2 face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=788465906-09052017><FONT color=#0000ff
size=2 face=Arial>Tantalizingly close, but alas, no cigar.</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=788465906-09052017><FONT color=#0000ff
size=2 face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=788465906-09052017></SPAN> </DIV>
<DIV dir=ltr align=left>
<HR tabIndex=-1>
</DIV>
<DIV dir=ltr align=left><FONT size=2 face=Tahoma><B>From:</B> Quincas Moreira
[mailto:quincas@gmail.com] <BR><B>Sent:</B> Monday, May 08, 2017 9:29
PM<BR><B>To:</B> David G Dixon<BR><B>Cc:</B> Adam Inglis; synth-diy mailing
list<BR><B>Subject:</B> Re: [sdiy] MS-20 tempco (was Model D
service)<BR></FONT><BR></DIV>
<BLOCKQUOTE
style="BORDER-LEFT: #0000ff 2px solid; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; MARGIN-RIGHT: 0px"
dir=ltr>
<DIV></DIV>
<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
style="BORDER-LEFT: #ccc 1px solid; MARGIN: 0px 0px 0px 0.8ex; PADDING-LEFT: 1ex"
class=gmail_quote><U></U>
<DIV style="WORD-WRAP: break-word">
<DIV dir=ltr align=left><SPAN
class=m_-2223816546397876983088021704-09052017><FONT color=#0000ff size=2
face=Arial>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 color=#0000ff size=2
face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN
class=m_-2223816546397876983088021704-09052017><FONT color=#0000ff size=2
face=Arial>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 color=#0000ff size=2
face=Arial></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN
class=m_-2223816546397876983088021704-09052017><FONT color=#0000ff size=2
face=Arial>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 lang=en-us class=m_-2223816546397876983OutlookMessageHeader
align=left>
<HR>
<FONT size=2 face=Tahoma><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>>>>
______________________________<WBR>_________________<BR>>>>
Synth-diy mailing list<BR>>>> <A
href="mailto:Synth-diy@synth-diy.org"
target=_blank>Synth-diy@synth-diy.org</A><BR>>>> <A
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target=_blank>http://synth-diy.org/mailman/l<WBR>istinfo/synth-diy</A><BR>>><BR>>>
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clear=all><BR>-- <BR>
<DIV class=gmail_signature data-smartmail="gmail_signature">Quincas
Moreira<BR>Test Pilot at VBrazil Modular</DIV></DIV></BLOCKQUOTE></BODY></HTML>