Replacement JFET for ASM-1 VCO

Tony Clark clark at andrews.edu
Wed Nov 3 18:52:11 CET 1999


> Tony, 
> 50C, 55C, even 70C is nothing unusual for consumer devices.
> Look into the specs of the manufacturers.

   Well yes, I know that specs extend up to 125C for a lot of devices and 
that most manufacturers start derating at around 60C or so.  That wasn't 
my point.

> Note that Ta is not to be measured on your sofa (;->), but -say- 1mm above
> the device. Air is a very good insulator for heat, there can be large
> gradients. So, 50C is nothing unusal. Consumer products are tested
> with Tj=55C, normal consumer with Tj=70C, automotive even with Tj=120C
> (at least here at Micronas, but other manufacturers spec the same).

   Well, yes, in the majority of circumstances, we aren't talking about 
sofa temperature!  But in the case where there are no parts that are 
generating that kind of temperature, or no circuits nearby to produce it, 
sofa temperature is about all that's left.  
   I know that a typical VCO probably isn't going to be generating an 
ambient temperature of 50C even at 1mm above the devices.  I just doubt 
that much power is being dissapated.  And since I keep my power supplies 
in an isolated box, I doubt that there would be anything else to generate 
that kind of heat, even if it is small in terms of what the devices can 
handle.
 
> After a few hours my Roland M480 mixer get's pretty warm OUTSIDE, I guess
> 40C or more. That means: inside is hell, the chips run perhaps as high
> as 70C.

   Again, my point was that I don't like to run circuits this hot.  After 
all, its too easy to provide adequate ventilation, or at least, to 
separate heat generating sources from the rest of the system.
   My personal favorite, the Matrix 1000.  The case on it gets pretty 
darn warm and I know there ain't much room inside...

   Tony

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I can't drive (my Moog) 55!         |     The E-Music DIY Archive
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Tony Clark -- clark at andrews.edu     | aupe.phys.andrews.edu/diy_archive
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