[sdiy] CA3046 Heater / Substrate Question

Simon Brouwer simon.o at brousant.nl
Sat May 7 11:42:54 CEST 2016


Hi,

The target temperature should be the maximum temperature the part could reach
without heating, under foreseeable usage conditions. 
IMO only if your synth has a serious heat accumulation problem and you plan to
sometimes play it in really hot weather would you need to set the heater to
65°C.

However, the use of setting it to 90°C would be in a test of how good the heater
would be at reaching a sensible temperature when you would play the instrument
under freezing conditions. 

Best regards
Simon.


> Op 6 mei 2016 om 14:14 schreef Steve <sleepy_dog at gmx.de>:
> 
> 
> I've never done this, but do you really need 65°C?
> Wouldn't 40..45°C suffice? And you could perhaps put some thermally isolating
> foam around the IC, if the layout allows it? Then you'd not need to heat so
> much to be stronger than the surrounding heat I guess.
> Also... if the thing takes a minute to be operational, I personally couldn't
> care less, the guitarist also needs to heat up his gear :-)
> 
> Steve
> 
> 
> 
> 
> 
> Von: "Nils Pipenbrinck" <n.pipenbrinck at hilbert-space.de>
> An: synth-diy at dropmix.xs4all.nl
> Betreff: Re: [sdiy] CA3046 Heater / Substrate Question
> 
> [...]
> 
> > BTW, "better" is an enemy of "good". What is wrong with just 1
> > transistor heater?
> 
> There is nothing wrong with it, but it's not ideal because the 1
> transistor heater can only dissipate 300mW. The cooling of the package
> takes away a big chunk of the energy we put into heating. So reaching
> tuning stability is slower than it could be.
> 
> 
> I did some measurements yesterday, measuring the Vbe drop directly while
> heating with two different target temperatures. I faked a bit, left the
> substrate transistor connected as usual and used one of the matched pair
> transistors as my second heater:
> 
> http://torus.untergrund.net/synth/heater_65deg.png
> 
> Here I aim at 65°C. You'll see that the two transistor circuit reaches
> stability after 4 seconds while the one transistor circuit needs about
> 100 seconds:
> 
> http://torus.untergrund.net/synth/heater_90deg.png
> 
> Here I aim at about 90°C. The two trannie method reaches stability after
> half a minute while the single transistor never reaches it's target
> temperature and asymptotically drifts to somewhere around 70°
> 
> 
> I think this is a great improvement over the one transistor circuit, and
> the substrate transistor is unused, so why not use it as a second heater?
> 
> 
> Best,
> Nils
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