Could someone do a 'back-of-envelope' calculation of the thermal time constant for a 1/4W resistor? I suspect it will show that thermal effects are too slow to generate harmonic or normal IM distortion from constant tones, but might (just) give rise to music envelope type effects? I note that John mentioned thermal capacity. The instantaneous element temperature of a small resistor could vary much more quickly than the surface temp, and of course it is the element temp which affects the tempco.
John,
They are really too expensive for commercial production, but I LOVE the Rohpoint Noninductive Wirewound copper alloy resistors. A tempco of Feck All, 0.01% tolerance as standard and they sound generally like a piece of wire, decent wire. Next to some audiophile stuff at only 5-10 quid or so per piece they are divine.
Yes, resistor quality is a b.i.t.c.h. At AMR we now use some "magic" ;-) SMD parts, they even measure much better than generica, never mind sound.
Yes, I know this.
At AMR we now use some "magic" SMD resistors. They make a quite dramatic improvement subjectively and pass DBT vs. generica. The only time I could ever measure the difference was excess noise when used in the tail of a folded cascode used as MC pre-pre and even then it was only one in 5 resistors that showed excess noise.
Ciao T
They are really too expensive for commercial production, but I LOVE the Rohpoint Noninductive Wirewound copper alloy resistors. A tempco of Feck All, 0.01% tolerance as standard and they sound generally like a piece of wire, decent wire. Next to some audiophile stuff at only 5-10 quid or so per piece they are divine.
Yes, resistor quality is a b.i.t.c.h. At AMR we now use some "magic" ;-) SMD parts, they even measure much better than generica, never mind sound.
Yes, I know this.
At AMR we now use some "magic" SMD resistors. They make a quite dramatic improvement subjectively and pass DBT vs. generica. The only time I could ever measure the difference was excess noise when used in the tail of a folded cascode used as MC pre-pre and even then it was only one in 5 resistors that showed excess noise.
Ciao T
Maybe John couldn't measure the difference at that time. (And maybe even T today! Cross posted!)
It gets a bit more interesting these days.
Even a geek with a computer and an A/D can measure a lot of things that used to be at the very least difficult.
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i would be willing to place a large wager that you can measure the temperature coefficient's affect on distortion versus frequency even at levels as low as 1/4 rated power.
! ! ! (How come there is no emoticon for sharks teeth?)
There is no RATIONAL reason why the 'vishay' resistor did what it did. However, it was a wake up call for me to keep to 'what works' rather than what measures OK. The Asian Vishay resistor was tiny, but had a fairly high power rating, maybe 1/3W, and a great TEMPCO. (Hey guys, I do this for a living) It was MORE EXPENSIVE than the Holco it replaced. And finally, I was not on the listening committee who evaluated the differences between the two resistors in Texas. It was my CTC business partner, Bob Crump who did the listening with his friends. Ask Bear about Bob, sometime. RIP Bob.
No one. And sine waves aren't static. What a curious thing for you to say.
You won't see much- it takes a LOT of IR to significantly heat those sort of high specific heat materials. I used to do photoacoustic spectroscopy, which relied on just that sort of effect, and it took quite sophisticated lock-in amps to see the signals.
Thanks. I have just weighed some resistors. Including leads, 0.25W metal film are about 0.2g, 3W metal film are 1g. Up to half of the weight could be the leads (wild guess?) so a ballpark figure is around 0.5 secs for 0.25W? Plenty of scope for music-envelope-level temperature variations. Possibly some scope for temperature-induced crossmodulation.SY said:
The heat is generated in the resistive element, and this is the temperature sensitive part too. So for carbon comp we have poor linearity but a big element to absorb heat, for carbon film we have a very small element but reasonably good tempco. This problem, if it exists, would not show up in harmonic distortion except possibly at very low frequencies or for small-difference-frequency IM.
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Part of me would like to say this can't be it is just a resistor. But experience has shown it to be the case over and over it all matters at this level. Good listeners you trust are important sounds like you lost one.
Wow! All standard quality metalized resistors have 50 ppm and we use them at no more than 1/10 rated power .....
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