[R-390] Resistors
Jim M.
jmiller1706 at cfl.rr.com
Tue Jan 3 19:24:46 EST 2006
Quoted From: http://www.dataforth.com/catalog/doc_1065.html
Resistor Thermal Noise
Quote: "There are ... subtle sources of noise that often go unrecognized.
Electrons within a conducting media or a semiconductor device that are
available to move are responsible for current flow (charge per second) when
excited by external voltages. With no externally applied voltages, electrons
are still in motion randomly interacting with other electrons and with the
material's lattice sites and/or impurities; however, their average velocity
in any direction remains zero (i.e. no current flows). This statistically
random electron motion creates noise voltages whether there is an applied
external voltage or not. Consequently, conducting media generates internal
noise without current flow.
Additional types of noise occur when current flows. The random statistical
nature of trillions of electrons traveling with an average velocity in the
same direction traversing random paths and interacting with material lattice
sites will create several types of noise. In many instances, these noise
voltages will seriously affect instrumentation. The laws of material physics
and quantum mechanics which govern electron motion are random and,
therefore, behavior models must be treated with statistical methods. This
means that noise voltages are typically expressed as a "mean square" value.
One common noise category is resistor thermal noise, which is the noise
developed in a resistor in the absence of current flow. Thermal noise was
modeled by Nyquest in 1928 and experimentally measured by Johnson. This
noise, often referred to as "Johnson" noise, is generated in a resistor
independent of any current flow and has a mean-square voltage value of
4*k*T*R*(BW). In this expression "k" is Boltzman's constant, "T" is
temperature in degrees Kelvin, "R" is resistance in ohms, and "BW" is
bandwidth, in Hz.. For example, at 100 degrees C, the noise voltage measured
with an ideal true RMS 1 Meg Hz bandwidth voltmeter within a 500k ohm
resistor is approximately 100 micro-volts. Clearly, this can cause serious
errors when measuring low level voltages with high gain signal conditioning
modules. ..."
See also
http://www.tutorialsweb.com/rf-measurements/noise-figure/noise-in-electronic-components.htm
Also from
http://www.physics.ucdavis.edu/Classes/Physics122/Phys122_Johnson_Noise.pdf
you will need some math
Jim M. N4BE
----- Original Message -----
From: "Barry Hauser" <barry at hausernet.com>
To: "bernie nicholson" <vk2abn at bigpond.net.au>; <r-390 at mailman.qth.net>;
"Roy Morgan" <roy.morgan at nist.gov>
Sent: Tuesday, January 03, 2006 10:39 AM
Subject: Re: [R-390] Resistors
> Hi Roy
>
> Thanks for the explanation. Of course, now I'll be listening for oboes
> and clarinets ;-).
>
> It's difficult to say what the audio builders think as a lot of that stuff
> is now mixed with lore, urban legend, and maybe a large dose of hype (as
> in monster cables, oxygen, etc.)
>
> I think part of the reason for favoring carbon comps is avoidance of
> inductance or capacitance introduced by metal or carbon film resistors --
> whether real or imagined.
>
> Some audiophile restorers seem to be looking to preserve whatever
> component characteristics inherent in the old tube designs -- good, bad or
> indifferent -- to maintain that warm, fuzzy 50's feeling or whatever.
> This ranges into the fringe area where used Black Beauties fetch high
> prices.
>
> This is not to poke fun -- I really don't know -- but merely suggest that
> the reasons for favoring this or that type of component do not necessarily
> fall along familiar parametric lines, known elements of the laws of
> physics and chemistry, electricity, etc. I suppose if your objective is
> to retain authentic performance, including distortion and noise, it would
> make sense to stay with components of identical or similar construction --
> providing functional components of the type can be found today.
>
> As I recall, there was a thread some years ago about whether or not a
> modern carbon film resistor might cause a problem somewhere in the R-390A
> if used as a replacement for a carbon comp. I think the conclusion -- at
> least the one I drew from the thread -- was that it might affect one or
> two areas, but generally no problem and not worth worrying about..
>
> Barry
>
>
>
>
>
>
> ----- Original Message -----
> From: "Roy Morgan" <roy.morgan at nist.gov>
> To: "bernie nicholson" <vk2abn at bigpond.net.au>; <r-390 at mailman.qth.net>
> Sent: Tuesday, January 03, 2006 9:37 AM
> Subject: Re: [R-390] Resistors
>
>
>> At 12:07 AM 1/3/2006, bernie nicholson wrote:
>>>Guys I don't want to be PICKY but WHAT is a LOW NOISE
>>>RESISTOR????????????
>>
>> Bernie,
>>
>> A perfectly good question!
>>
>> It turns out that anything that is not very very very cold makes
>> electrical noise. (That means near absolute zero - minus 273 degrees
>> Centigrade or some such.) The phenomenon is based on the fact that
>> molecules move about if they are at any temperature above absolute zero.
>> This does not matter much to R-390A/URR users, though it does to folks
>> doing radio astronomy and folks building detectors to sense submerged
>> submarines from bumps in the earth's magnetic they produce. But I
>> digress.
>>
>> If you put some current through a resistor, the material makes additional
>> electrical noise. Some resistor materials make more than others, current
>> and voltages being equal. It appears that folks who build phonograph
>> cartridge amplifiers and low noise VHF receivers can tell the difference
>> between such resistors.
>>
>> Almost all the noise from a properly aligned R-390A/URR receiver is
>> generated in the first RF amplifier tube. It's quite possible that if
>> the resistors around that tube are particularly noisy, they will
>> contribute a noticeable amount to the receiver noise. If the IF gain is
>> set very much too high, the IF amplifier will make noticeable noise. This
>> is bad. Any IF amplfier makes measurable noise, and Roger has been
>> telling us how to measure that, and to select tubes to reduce that noise.
>>
>> Additional noise is generated in the mixer tubes. Some tube substitutions
>> suggested in modification articles make less noise than the ones normally
>> used in the R-390A. I have not tried these changes, but I hope to one
>> day. I have a spare RF deck for the purpose.
>>
>> It's the opinion of experienced radio users that very very few of us live
>> in places where the received noise level is low enough so that the noise
>> generated in a receiver is of much matter at all. On HF, that is. Above
>> 30 mc it's a different matter.
>>
>> Faulty (that is leaky) RF and IF bypass caps definitely make noise.
>> After you have found this going on, and fixed it a number of times, the
>> noise from this source is quite distinguishable from other noise. It's
>> sort of like telling the difference between an oboe and a clarinet.
>>
>> As I understand it, carbon composition resistors are favored by the high
>> fi builders for low noise and for other differences they hear in the
>> sound. And they also report that some other resistors are better for
>> noise.
>>
>> I would be glad to hear about any perceived or measured differences in
>> noise in the R-390 receivers due to resistor changes..
>>
>>
>> Roy
>>
>> - Roy Morgan, K1LKY since 1959 - Keep 'em Glowing!
>> 7130 Panorama Drive, Derwood MD 20855
>> Home: 301-330-8828 Cell 301-928-7794
>> Work: Voice: 301-975-3254, Fax: 301-948-6213
>> roy.morgan at nist.gov --
>>
>> _____________________________________________________________
>> R-390 mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/r-390
>> Help: http://mailman.qth.net/faq.htm
>> Post: mailto:R-390 at mailman.qth.net
>> Unsubscribe: http://mailman.qth.net/mailman/options/r-390
>>
>
> _____________________________________________________________
> R-390 mailing list
> Home: http://mailman.qth.net/mailman/listinfo/r-390
> Help: http://mailman.qth.net/faq.htm
> Post: mailto:R-390 at mailman.qth.net
> Unsubscribe: http://mailman.qth.net/mailman/options/r-390
>
More information about the R-390
mailing list