[sdiy] Making toast with chips

[Richard Wentk]

At 21:01 27/11/2002 +0000, Lincoln Fong wrote:

>Can anyone tell me if Opamps should ever run hot (to the touch) and what
>it implies if they are? I notice on some audio boards I'm looking at
>that the NE5532s (and 5534s) are hot to the touch. Some hotter than
>others.

Tim Orr of EMS and Powertran fame had a rule - if you can keep your finger 
on it, it's cool.

30-odd degrees C I'd ignore as a non-issue. 40-odd would be mild cause for 
concern but I'd let it go, especially if it were only a couple of chips in 
an entire unit. If I had a board full of chips cooking at 40+ degrees, that 
would give me pause for thought.

50-odd I'd definitely do something about, if only because if you have a lot 
of chips sweating you start getting other problems.

And 60-odd plus is completely unacceptable, especially for synth hardware. 
If nothing else I'd expect eventual reliability problems.

For comparison, processor chips like the Athlon will work up to around 60 
degrees. I find if I let my 2100XP+ get any hotter, it starts misbehaving. 
I'd expect analogue to be more forgiving, but I still wouldn't push it. 
Thermal cycling does put a physical strain on ICs, and is generally 
something you want to avoid.

If you find an opamp that's getting hot, stability is always a good thing 
to check. Stick a scope across it and you'll sometimes find it's 
oscillating like crazy at 50kHz or so. Kill that with an adjusted cap value 
and the problem goes away.

Richard