[sdiy] expo pair "heat shield?"

[Quincas Moreira]

I use heat shrink tubing, learned it from Ray Wilson on the Soundlab Mk 2
build guide. With a little heat sink paste on top coupling the tempco and
the transistor pair

On Tue 11 Oct 2022 at 20:38 Neil Harper via Synth-diy <
synth-diy at synth-diy.org> wrote:

>
>
> On 10/11/22 14:25, Mattias Rickardsson wrote:
>
> > If there are very nearby objects with strong pulsating heat, which
> > affects one transistor more than the other, then a heat shield might do
> > some good. There probably aren't! (-:
> >
> > (I assume that "shield" means metal foil or some other reflective
> > material, not just any material that is in the way but absorbs incoming
> > heat)
> >
> > What's most important is to keep the pair at identical temperatures,
> > which is done by having substantially less thermal resistance between
> > the transistors compared to between the pair and their environment. But
> > it's important that they are not totally isolated - if the contact
> > between pair and environment is very weak, such as using a shield that
> > reflects heat from the transistors back on themselves, then there will
> > be increased self-heating effects with different temperatures depending
> > on the currents through the transistors. Not optimal. I guess the
> > component legs would give enough contact in most normal cases though.
> >
> > Making some kind of blob around the pair in order to increase thermal
> > inertia... Well, might be somewhat useful, but also potentially give
> > some of the self-heating problems mentioned above. Keeping them at one
> > constant temperature is the second important thing.
> >
> > Don't forget to optimize the inter-transistor contact first. Thermal
> > paste between them and something like shrink tubing around them should
> > do. :-)
> >
> > /mr
>
>
>
> thanks matthias, that's some good advice..
>
> i'm actually using a matched-pair on a single tiny SOT363 IC that I
> managed to hand solder. the tempco resistor just goes right overtop of
> it, in direct contact. so far I haven't added any additional thermal
> paste between the junction or done anything else.
>
> I thought maybe adding the hot-snot would isolate it from actual
> convection currents inside the eurorack enclosure.
>
> but i suppose the most important thing is just that entire enclosure get
> up to an "operating temperature" and remain there, and that the
> transistor pair and resistor also get up to this same temperature. I
> suppose if it's 'insulated' in any, it is still destined to eventually
> reach that operating temperature, but might just take longer to get
> there.. which isn't any benefit. and good call on insulation possibly
> keeping any self-generated heat in, instead of letting it dissipate..
>
>
>
> --
> /// Neil Harper
> /// Every Wave is New Until it Breaks
>
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-- 
[image: QMA]

Quincas Moreira
Director | QMA
mobile:  5534988825
site:  quincasmoreira.com
email:  quincas at gmail.com
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