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billshurv 16th September 2020 12:30 PM

Why use high power handling resistors for microwatt levels?

SemperFi 16th September 2020 01:54 PM


Originally Posted by analog_sa (
Hard to say as there are too little data points so far. To my embarrassment i still have not conducted any listening tests of smd resistors. It seems most of the better products use Melf, so those would be first on my list to compare to familiar tht resistors.

The uncertainty is generally discouraging me from using smd resistors, even though the absence of leads and caps seems like a good thing.

I am actually not in disfavor of possible variances due to types of resistors. The smaller they get, the more their tempcos will start to effect their actual resistance, since the voltage levels mostly stay the same in audio. The current density also can get to a point where excess noise starts to be a factor. But at those voltage swings the music should be so loud that the excess noise only a tiny speck in the mix, totally inaudible.
I do find the subject interesting tho if only to have the possible option of getting a dB or so better NF or distortion, but not so much because I think I can hear it.

Vovk Z 16th September 2020 02:27 PM


Originally Posted by escksu (
So, I am wondering if we are able to hear any differences in these resistors. Will a foil resistor sound very different from a thin film one??

Rather not, then yes. Thin film resistors have good enough properties to they were 'non audible' in audio circuits if they were right chosen (rated power with good enough margin etc).

Vovk Z 16th September 2020 02:34 PM


Originally Posted by billshurv (
Why use high power handling resistors for microwatt levels?

TCR and ppm.

Conrad Hoffman 16th September 2020 02:39 PM

I don't know about sonic differences but thick film resistors can have a larger voltage coefficient than thin film. They can also have more excess noise. Or not. You have to look at data sheets and possibly measure. Derating resistors can reduce those factors.

DPH 16th September 2020 03:10 PM

^ bootstrapping on the TC and voltage coefficient issues, here's a link (from Bonsai's site!) to an article by Bruce Hofer, of Audio Precision, on these issues. It dovetails into what I said earlier about this being a topic that the details matter after plenty of electronics experience, not the beginner.

Indiglo 16th September 2020 04:47 PM

Here are some measurements of distortion between a normal 1206 smd resistor and a MELF resistor in the feedback path, whilst there will be no audible differences it will be important from an engineering perspective if for example you were designing a low distortion signal generator to used as test equipment.

Even order distortion in symmetrical amp

billshurv 16th September 2020 05:43 PM


Originally Posted by Vovk Z (
TCR and ppm.

I repeat the question. For a load resistor what is the issue?

Mark Tillotson 16th September 2020 06:06 PM


Originally Posted by Indiglo (
There are no sonic differences. It's audiophile mythology.

Not quite true I'm afraid, its very possible to measure the difference between the various sorts and even sizes of SMT resistor with good equipment. Its rare for datasheets for SMT resistors to include the data you need to predict the audio performance - i.e. voltage coefficient and various excess noise parameters.

Thick film are metal oxide (ruthenium oxide in glass typically), and perform distinctly less well w.r.t. distortion and noise than thin-film (which are metal film by another name). Typical voltage coefficients for thick film are 30--100ppm,
versus ~1ppm for thin-film. If you want < 0.01% distortion metal oxide are to be avoided.

Larger sized SMT resistors tend to have less excess noise and less distortion as voltage coefficient depends on electric field strength - so larger thin-film (1206, 1210 or more) are needed to compete against standard 1/4W through-hole metal film, (although this is likely beyond audibility and most measurement equipment!)

Basically for the performance-defining components (filter components, feedback
networks) you need thin-film to assure metal-film levels of performance, and for high-voltage swings the larger package sizes are advised to match through-hole performance levels.

Doug Self goes into a lot of detail of resistor performance in Chapter 2 of "Small Signal Audio Design".

scottjoplin 16th September 2020 08:05 PM


Originally Posted by escksu (
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