[sdiy] CA3046 Heater / Substrate Question

[Nils Pipenbrinck]

Hi again.

I'll put the answers to your posts into one mail.

But first: I got it working!

Romans comment was spot on. In case of no heating there was a current 
transfer through the two load resistors which messed up the substrate 
voltage.

Now I just block the unwanted current flow with a diode and et voilà: It 
works like a charm. Here is the relevant part of the heater circuit:

   http://torus.untergrund.net/synth/heater2.png


On 05/06/2016 02:29 PM, Roman Sowa wrote:
> I see your point. How about potting the chip in a blob of polyurethane
> foam? Looks utterly ugly and pain to repair, but not much heat escape
> then and 300mW will be more than enough.

I tried that, and it does improve the heating somewhat, but less than I 
expected. I thing a good chunk of the heat leaves the chip through the 
leads into the PCB copper, and not via the plastic case to the air.


On 05/06/2016 02:14 PM, Steve wrote:
 > I've never done this, but do you really need 65°C?

Overall the circuit should end up in a four channel "chord" synth for 
live performance. I'll run the heater a bit higher than the suggested 
40° just because I expect the case to run quite hot in the summer sun.


On 05/06/2016 07:35 PM, Rick Jansen wrote:
 > I'd say 40-ish is fine,
 > as long as you don't run the circuit in the Sahara.

I've been told every once in a while musicians get challenged to 
rock-out against shiny demons and devils. Having the option to run at 
hellish temperatures is a good thing to have :-)


Thank you all for your help.

Best,
   Nils