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In Reply to: RE: Heating and cooling nonlinear power devices. posted by pictureguy on June 29, 2011 at 10:34:37
Thermal time constants can only be ignored for far out-of-band signals like 'DC'. Since the discussion is about potential distortion products they are in play because they can cause IM.
Another area that can cause serious problems, especially for power resistors, is the termination where the metal with the deliberately 'high' resistance (and hence running hot and cold) transitions to the leads or tabs. I have some large resistors that I use for working on power supplies that have become virtually unusable from this problem.
Regards, Rick
Follow Ups:
I know stuff wears out. Everything.
But, will a resistor run within power rating given a 'conservative' design, be subject to early fatigue death? I've seen boards where the place under a 10 watt carbon has been heat charred...but this was in gear run 24/7. (semiconductor fabrication equipment)
Were the dead resistors you refer to always run within design limits or a little edgier?
And IM distortion? Short of LN2 immersion, what can be done? Every circuit element has resistance and therefore heats. I don't know how much a warm inductor changes, but certainly semiconductors...discrete power devices or even low level integration of OPAMPS or even hi level integration.....
You're saying resistors change, too. All well and good, but how much and to what real effect that you can address?
These kinds of effects make sense if you're looking for ETs and have a radio dish listening stuff millions of light years away and SNR is beyond critical.....
Aren't all these effects pretty much the 'cost of doing business' with electronics?
I guess my question would be....
What does it do to my listening experience that I can actually do something about?
Too much is never enough
-Kurt
Edits: 07/05/11
"Were the dead resistors you refer to always run within design limits or a little edgier?"
Well I was running them within limits, but they were old and were given to me to boot so who knows? I bet part of it was corrosion.
"And IM distortion? Short of LN2 immersion, what can be done? Every circuit element has resistance and therefore heats."
There are a lot of things that can be done to reduce these sort of effects, you mention op-amps, thermal feedback is a major problem with monolithic linears especially ones with significant output power so as you are probably well aware great pains are taken to use them differentially and to make the die symmetric so that the heat from the output stage couples equally to both sides canceling out the thermal terms. Mostly.
For resistors you reduce their dissipation, reduce their thermal resistance to air or increase their thermal mass to try and even out their highs and lows. The average power TC may cause a little compression or expansion but I'd guess it's not as audible as bass altering your high's levels when someone hits a drum. All that being said I'm not aware of ever having audible problems from the TC of resistors.
As far as sensitivity to these sorts of things go I think audio gear is right up there, our hearing can really eke out deep details.
Regards Rick
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