what is a noisy resistor anyway/

et...@whidbey.com

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Dec 12, 2019, 1:39:53 PM12/12/19

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I have read about noisy resistors but what makes then noisy and what
exactly is the noise?
Thanks,
Eric

peterw...@gmail.com

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Dec 12, 2019, 2:00:34 PM12/12/19

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http://www.resistorguide.com/resistor-noise/

Peter Wieck
Melrose Park, PA

Mike Coon

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Dec 12, 2019, 3:06:01 PM12/12/19

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In article <63da826d-85c7-4b45...@googlegroups.com>,
peterw...@gmail.com says...

The interesting discussion provides an equation for the noise level that
has no term for a material characteristic. Then goes on to say that
there are quiet and noisy constructions. This seems to me a
contradiction which is not resolved!

Mike.

John Robertson

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Dec 12, 2019, 4:42:25 PM12/12/19

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Also, some resistors are only noisy under power (load). The Heathkit
Audio Signal Tracer had a NOISE function where it would put about 75 -
100VDC across a resistor using the audio probe and if the resistor was
noisy you could hear it...

Handy test on tube sets!

John :-#)#

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Phil Hobbs

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Dec 12, 2019, 5:35:22 PM12/12/19

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On 2019-12-12 14:00, pf...@aol.com wrote:
> On Thursday, December 12, 2019 at 1:39:53 PM UTC-5, et...@whidbey.com wrote:
>> I have read about noisy resistors but what makes then noisy and what
>> exactly is the noise?
>> Thanks,
>> Eric
>
> http://www.resistorguide.com/resistor-noise/

That's a really bad article.

All resistors have Johnson (thermal) noise, which is white (i.e. flat
with frequency). Resistors of the same value all have the same Johnson
noise, but they differ a lot in their low-frequency noise.

Some types of resistor, e.g. thick film, cermet, and carbon film,
exhibit large fluctuations in conductance. Those don't cause problems
if there's no DC voltage applied, but if there is, the conductance
fluctuations turn into noise currents with an approximate 1/f power
spectrum.

Because of that 1/f, these types of resistor are very noisy at low
frequency when there's DC applied.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

tabb...@gmail.com

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Dec 12, 2019, 9:28:34 PM12/12/19

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On Thursday, 12 December 2019 22:35:22 UTC, Phil Hobbs wrote:
> On 2019-12-12 14:00, pf...@aol.com wrote:
> > On Thursday, December 12, 2019 at 1:39:53 PM UTC-5, et...@whidbey.com wrote:
> >> I have read about noisy resistors but what makes then noisy and what
> >> exactly is the noise?
> >> Thanks,
> >> Eric
> >
> > http://www.resistorguide.com/resistor-noise/
>
> That's a really bad article.
>
> All resistors have Johnson (thermal) noise, which is white (i.e. flat
> with frequency). Resistors of the same value all have the same Johnson
> noise, but they differ a lot in their low-frequency noise.
>
> Some types of resistor, e.g. thick film, cermet, and carbon film,
> exhibit large fluctuations in conductance. Those don't cause problems
> if there's no DC voltage applied, but if there is, the conductance
> fluctuations turn into noise currents with an approximate 1/f power
> spectrum.
>
> Because of that 1/f, these types of resistor are very noisy at low
> frequency when there's DC applied.
>
> Cheers
>
> Phil Hobbs

And a 'noisy resistor' is one that has become faulty in that it generates a lot of extra noise. Classic issue with carbon comps.

NT