[sdiy] expo pair "heat shield?"

[mskala at northcoastsynthesis.com]

On Tue, 11 Oct 2022, Neil Harper via Synth-diy wrote:

> just wondering if anybody thinks it's worth encasing an exponential pair
> for stability. while this is in my modular case, there must be some heat
> currents moving around from the other stuff that share the same space.
>
> Maybe a dab of hot-glue-gun (hot snot), or a silicone or something?

I put two TO-92 transistors face to face, with a cable tie to hold them
together tightly, and I usually also add a dab of general-purpose plastic
glue on top to keep the cable tie from sliding off.  I don't know if
that's absolutely optimal, but I think it's good enough for the VCFs in
which I use it.

The next meaningful level up would be having the transistors on the same
die; and the level after that would be a temperature-controlled oven.  I
don't think just insulating or shielding them without those measures would
make much difference - stuff like self-heating effects will be bigger than
air currents in most cases, given that you're already using a pair of
transistors.  Having two transistors means anything that affects both of
them, like general ambient temperature variation, should already be at
least partially compensated.

-- 
Matthew Skala
North Coast Synthesis Ltd.