Metrology grade audio resistors (for only the most resolving audiophiles)

[sahko123]

I'm looking to create a little resistance standard to be able to take some ppm's home from work using their gold 3458A.

The construction will be just a simple box metal or 3d depending on how much effort and money I wish to put in. It will have the obligatory kelvin binding post to ensure proper measuring of course.
This is most likely the resistor I will use.
(Ultraprecision resistor)
https://4donline.ihs.com/images/VipMasterIC/IC/VIPG/VIPG-S-A0002790024/VIPG-S-A0002790024-1.pdf?hkey=6D3A4C79FDBF58556ACFDE234799DDF0

Here however is the topic up for discussion
(Weird audio specific naked/un-encapsulated Z-foil resistor)
https://www.farnell.com/datasheets/1911181.pdf

Has anyone used these for anything uniquely useful? Can these ACTUALLY be utilised for something useful? Or are they just another case of audiophile audio-f**ckery? I'm thinking they may allow for custom encapsulation options with even the possibility of custom hermitic sealing or oil submersion for whatever reason.

[gamalot]

They claim the naked version is used to reduce signal distortion and improve signal processing clarity, and since there is no hermetically sealed they will be more sensitive to humidity changes, I think.

[Kleinstein]

The naked version could be an alternative to the epoxy molded version. It does not have the extra protection, but also not the possible stress from the molding. So expect a different effect from humidity: possibly a faster response and maybe additional aging from the lack of protection, but also less / non of the delayed effect (time constant in the weeks range) from the swelling that makes up most of the humidity effect in the molded version.

In a good protective case it may be a good choice.

[magic]

Regarding distortion and "clarity", here's teardown of a TOTL audio analyzer, so you can see what sort of resistors they use.
http://archimago.blogspot.com/2020/07/pictures-audio-precision-apx555-b.html

Some of them may possibly be metal foil (or not), but it doesn't look like there is any of that "naked" stuff in there.

Probably marketing wank. Perhaps they wouldn't market them as "audio resistors" if they were good for DC.

[sahko123]

Do you reckon putting this one in an epoxy filled enclosure would be better or would there be too much internal stress?

[Conrad Hoffman]

No idea of their intrinsic goodness, but it seems like something that you could put in a small hermetic housing with some desiccant and then back fill with dry nitrogen. Naturally you'd want to eliminate all lead stress with proper loops and bending.

Somewhere, long ago, Audio Precision published something on resistors that showed the metal foil parts were actually inferior for audio. I can't find the original article but some discussion here- https://www.diyaudio.com/community/threads/low-frequency-modulation-distortion-in-foil-resistors.237237/

edit- I think this is the original AP article- https://documen.site/download/measuring-class-d-amplifiers_pdf

[Kleinstein]

Putting epoxy on the resistors is at least risky and not a good idea:
Much of the humidity sensitivity in the potted resistors likely comes from epoxy swelling from humidity and causing stress on the resistors.
The epoxy one is mixing in small scale is most likely inferior to the one used for the ready made potted ones.

The use would be more with the resistor as is in a closed case. The question here still is wether to seal it to slow down to exchange with the outside or keep some pressure relief to avoid mechanical stress from changes in the air pressure.

[guenthert]

No idea of their intrinsic goodness, but it seems like something that you could put in a small hermetic housing with some desiccant and then back fill with dry nitrogen.

     Wouldn't be oil the more traditional choice?  Probably also easier to seal and detect leakage.

Then again, I can never tell when you guys are serious.  I'm surprised that Vishay caters to the audiphools now.

[MiDi]

Wouldn't be oil the more traditional choice?  Probably also easier to seal and detect leakage.

Then again, I can never tell when you guys are serious.  I'm surprised that Vishay caters to the audiphools now.

White oil e.g. transformer oil or (uncommon) silicone oil.
Those Vishay audio resistors are awailable for long time.
You can get custom ones e.g. from Texas components.

[Conrad Hoffman]

I made the suggestion because that's how General Radio did their reference capacitors and it's a very clean way to do things. Oil has its own set of problems, though the probability of success is high. I don't know how foil resistors are bonded, nor if oil will have any long term effect on them. Look up what people worry about with the classic L&N resistors. Oil can become acidic and should be changed periodically. It will, of course, help your power handling immensely.

[1audio]

Vishay has been selling resistors to Audio types for 40 years. He never ignored a profitable market. . .

However I would submit that the handling involved with a naked resistor could introduce more errors than working with a packaged hermetic resistor. Soldering will potentially cause a change with a hermetic package. The naked version is much more exposed and likely to get tweaked in handling.

The distortion AP identified in the Vishay foil resistors comes from the thermal time constants between the foil and the substrate. They started out as strain gauges and Mr. Vishay figured out that an optimum combo of substrate and gauge will have close to zero tempco. A neat idea that lead to owning a large part of the passive electronic component business.