[sdiy] Thermal contact of exponential convertor components

[James Patchell]

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
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http://www.oldcrows.net/~patchell

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