[sdiy] Thermal contact of exponential convertor components

[allenre at umich.edu]

Well, setting the offset isn't much of a problem ,but you are right about the
scale drift, I want that to be as small as possible.

I've read about the method of calculating a precise value for the temp.
coefficient of the tempco, but I don't know how to calculate it for the
transistor pair.  I have many 2SC1583s, and if I could calculate the
coefficients I could match them to the closest tempco.

Ryan

> Never calibrating a VCO is probably not at all possible.  You will have two
> different drifts...an offset drift and a scale drift.  The scale drift will
> be dependent on how closely you can match the temperature coefficient of
> the tempco resistor to that of the expo transistor pair.  If you are going
> to be doing pitch critical work, you will want this to be as close as
> possible.  Having to retune the scale every time you use the instrument is
> a pain in the neck, and retuning multiple oscillators is an even bigger
> pain...
>
> The offset drift might be annoying, but it is easy to take care of...just
> readjust the pitch knob on the front of the synth.  There are many sources
> to offset drift, the biggest one is the timing capacitor in the VCO.
>
> At 12:27 AM 5/17/2004 -0400, allenre at umich.edu wrote:
> >What I'm assuming is that, if I intend to use microtonal scaling to any
> degree
> >of accuracy then I will want very accurate compensation, right?  I'd also
> >prefer not to have to calibrate the VCOs _ever_ (maybe that's asking for
> >alot).
> >=)
> >
> >Ryan
> >
> > > Actually, getting the epoxy off isn't that hard....although, never had an
> > > expo transistor fail (must have made hundreds by now....), I do on
> occasion
> > > salvage the Q81K's for reuse.
> > >
> > > At 09:01 PM 5/16/2004 -0400, you wrote:
> > > >While the "quick and dirty" approach seems to be teh most popular, I
> > think I
> > > >will try the more professional looking heatsink compound with shrink
> > > >tubing.  I
> > > >may need to replace the 2SC1583 at some point and wouldn't want to
> damage
> > > the
> > > >tempco.
> > > >
> > > >Ryan
> > > >
> > > > > Same here....
> > > > >
> > > > > At 06:52 PM 5/16/2004 -0400, harrybissell wrote:
> > > > > >I just use epoxy...
> > > > > >
> > > > > >H^) harry
> > > > > >
> > > > > >allenre at umich.edu wrote:
> > > > > >
> > > > > > > I'm gathering parts for the Rene Schmitz's VCO3, and I am
> wondering
> > > if
> > > > > > I need to
> > > > > > > use heat sink compound on the transistor array and tempcos, or if
> I
> > > can
> > > > > > epoxy
> > > > > > > them together.  I'm not sure of the method of applying the heat
> > sink
> > > > > > compound.
> > > > > > > The ASM-1 page mentions that "The transistor ans the tempco
> > resistors
> > > > > > (if used)
> > > > > > > should be gooped up with heatsink compound... and tie-wrapped
> > > together,
> > > > > for
> > > > > > > best thermal result."  So, should I cover the components with the
> > > > > compound,
> > > > > > > then use a plastic tie-wrap to hold them close?  My
> > understanding is
> > > > > > that the
> > > > > > > heat sink compound helps to transfer heat, so I only need to
> > apply it
> > > > > > between
> > > > > > > the two components (in this case, a tempco and a 2SC1583), and
> the
> > > > > tie-wrap
> > > > > > > holds them together (since the compound is non-adhesive).  Is
> this
> > > > > correct?
> > > > > > > Thanks,
> > > > > > >
> > > > > > > Ryan Allen
> > > > >
> > > > >          -Jim
> > > > > ***************************************************************
> > > > > http://www.oldcrows.net/~patchell
> > > > >
> > > > > ***************************************************************
> > > > >
> > > > >
> > > > >
> > >
> > >          -Jim
> > > ***************************************************************
> > > http://www.oldcrows.net/~patchell
> > >
> > > ***************************************************************
> > >
> > >
> > >
>
>          -Jim
> ***************************************************************
> http://www.oldcrows.net/~patchell
>
> ***************************************************************
>
>
>