[sdiy] MS-20 tempco (was Model D service)

[matt holland]

ebers moll equation: Ic = Is*e^(Vbe/Vt -1)

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.



On Mon, May 8, 2017 at 5:36 PM, Tony K <weplar at gmail.com> wrote:

> Hello, those so-called special Rx's are 0.1% or precision resistors , the
> ones with the circle around the resistor symbol.
>
> 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.
>
>  Just referring to my notes , it's been a while.
>
> TK
>
> > On May 8, 2017, at 7:48 PM, Declare Update <declareupdate at gmail.com>
> wrote:
> >
> > 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?
> >
> > Chris
> >
> >> On May 7, 2017, at 4:14 PM, Michael E Caloroso <
> mec.forumreader at gmail.com> wrote:
> >>
> >> That's the one...
> >>
> >> MC
> >>
> >>> Anyway, I think Michael E C was referring to this posting of his:
> >>> http://search.retrosynth.com/ah/search/lookit.cgi?-v9901.2166
> >>
> >>
> >>>> On 5/7/17, Michael Zacherl <sdiy-mz01 at blauwurf.info> wrote:
> >>>>
> >>>>> On 7.May 2017, at 19:48 , Michael Zacherl <sdiy-mz01 at blauwurf.info>
> wrote:
> >>>>>
> >>>>> On 7.May 2017, at 19:04 , Quincas Moreira <quincas at gmail.com> wrote:
> >>>>>
> >>>>> Michael, thanks for saving me frustration, I will refer to your
> >>>>> instructions.
> >>>>
> >>>> uhm .. I didn’t do anything -
> >>>
> >>>
> >>> whoops  *blushes* … the other Michael.
> >>>
> >>> Anyway, I think Michael E C was referring to this posting of his:
> >>> http://search.retrosynth.com/ah/search/lookit.cgi?-v9901.2166
> >>>
> >>> sorry, Michael E C, Michael.
> >>>
> >>>
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