In article , John Larkin wrote: [.. Shot noise as phase noise ..]
Don't call me Shirly! :>
I think it is an extra noise source for high frequency PLLs and atomic clocks and the like. If it was only a variation in amplitude, it would not add any noise.
John, can you recommend resistors then? I'm not even sure what properties to look at. Some posters say TCR, some VCR (and for the latter I find it near impossible to find numbers from the manufacturer).
John Larkin wrote in news: snipped-for-privacy@4ax.com:
John Larkin wrote in news: snipped-for-privacy@4ax.com:
They call it "current noise" right in the abstract, as the Vishay people do.
Audio Note still makes tantalum oxide resistors.
Eeyore wrote in news: snipped-for-privacy@REMOVETHIS.hotmail.com:
For audio, any resistor, the cheapest thing in the Mouser catalog. In the unlikely case that there's a lot of DC across it, and the signal level is very low, one might argue against carbon comps, but that's about it.
And oh, in s.e.d. at least, we consider bottom-posting to be polite.
John
It is interesting; I'll try it soon. I have a nice selection of most everything - carbon film, metal films, cermets - but not much in the way of carbon comps.
I'm thinking 9 volt battery, small resistor and BFC filter cap, two identical 100K resistors as a voltage divider, Tek AM502 amp, rms DVM. That shouldn't be hard.
What's the math of the voltage divider as, say, my measured noise relative to the noise one resistor would show at that same (constant) current? I guess it's two noise sources connected in parallel, so
0.707?John
I've tried cermet potentiometers for volume control, and in a blind test (non-double, used dual switch with my friend) I can't tell the difference between it and a stepped attenuator; however, in 7/10 trials me and 8/10 trials him heard difference between plastic pot and the cermet, both preferring the cermet.
John Larkin wrote in news: snipped-for-privacy@4ax.com:
Er, by plastic pot I meant the conductive plastic ones such as Alps.
Prune wrote in news:Xns9808DFB222F42bobysgotgunsyahoocom@64.59.144.76:
I can't say I was aware that Alps made any conductive plastic types.
A better test would be Vishay-Sfernice's P11(cermet) vs PA11( conductive plastic)
Graham
The question is what was it you were hearing or thinking you were hearing ?
Graham
Let me guess: the Vishay metal resistors are more expensive than the others.
It looks like Vishay is trying to harvest some of the audiophool money. May we now expect disertations from smelters of oxygen-free copper and distillers of ultra-pure liguid nitrogen?
I don't have a Stereophile reviewer's vocabulary of terms to easily explain it. Suffice it to say it was a very small difference (I failed in 3 of the
10 trials). Subjectively, I'm limited to saying I liked the cermet a bit better, but it's hard to be more specific. If you're interested, you may wish to try a similar test yourself.I've been planning for a while to interface motorized switchboxes to the abchr computer program so this can be automated and one can do blind testing without a helper, but it's hard to find time among the various projects...
Eeyore wrote in news: snipped-for-privacy@REMOVETHIS.hotmail.com:
Your description would do actually, I'm not impressed by those f***wit reviews that talk about improving pace and speed one bit.
But how so ?
I wouldn't personally waste my time on something with no scientific basis i.e. cermet vs CP.
I do however have an interest in whether low-level vibration ( from the audio ) can cause issues in circuitry.
Graham
Eeyore wrote in news: snipped-for-privacy@REMOVETHIS.hotmail.com:
Parasitic capacitance of the conductive plastic is high. If the following stage has a high input impedance, it could make a frequency response difference.
Cermets have a problem that they wear down I guess. In any case, I always err on the safe side in that who knows whether a difference is too small by itself but may add up above a threshold when combined with other changes, so I ended up making a motorized step attenuator.
You mean by vibrating the wiper contact? I think the spring pressure is too high for that. I've only noticed vibration issues with tubes.
On Sat, 22 Jul 2006 13:28:45 -0700, John Larkin Gave us:
Anything above absolute zero not only emits IR energy, but electrical noise as well. (speaking of electrical mediums, of course)
Why do IR camera CCDs need LN baths? Noise floor.
On Sat, 22 Jul 2006 23:28:18 +0200, martin griffith Gave us:
Snip
Interesting discussion.
On Sun, 23 Jul 2006 04:59:19 GMT, Prune Gave us:
Have you tried to STOP TOP POSTING?
Prune wrote in news:Xns9808D3FC3201Cbobysgotgunsyahoocom@64.59.144.76:
They can call it George. The mechanism by which the noise is generated is that of shot noise. irregardless of the name.
mention
Naw, that ain't so.
Ohmite, KOA/Speer and other companies still make them. Yes, they're noisy in certain situations. Geetah-pickahs love the damn things, for some reason...so I sell 'em. If I'm replacing a resistor in a vintage amp, I use the same type - IF - the customer has specified that I must. Otherwise, it's metal film all the way. However, there are situations where performance in dealing with large transients is superior for carbon comps. You will note that carbon comps are available in SURFACE MOUNT packaging, so *somebody* with major engineering chops sees reasons to keep using them. The packaging is the expensive part, so there's probably no cost savings at all for carbon comp vs. metal film with surface mount.
Lord Valve Guitar Amp Wanker
That's how I've ever seen it described. The excess noise RMS voltage depends directly on I and not sqrt(I).
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