Low noise resistors

Archived from groups: rec.audio.tech (More info?)

Is it better to use over rated (higher wattage) resistors for low noise, or
just enough wattage capability to cover expected conditions plus a little
more for safty ?

My thinking is that over rating will result in cooler resistors, so therefore,
less noise, but, on the otherhand, more material for the signal to pass
through, therefore, more noise.
-Don

Archived from groups: rec.audio.tech (More info?)

>Is it better to use over rated (higher wattage) resistors for low noise, or
>just enough wattage capability to cover expected conditions plus a little
>more for safty ?
>
>My thinking is that over rating will result in cooler resistors, so therefore,
>less noise, but, on the otherhand, more material for the signal to pass
>through, therefore, more noise.

First thing would be to make sure that the resistors are adequately
de-rated to survive properly! Years ago, one of the early-generation
high-power transistor amps (the "Tigersaurus" ) developed a bad
reputation for failing after some period of use. It turned out that
the output stage used a "bias stack" of resistors, which were using
relatively small parts (1/2 watt?) but actually were dissipating
several times their rated amount of power. They cooked, and the amp
had a tendency to suffer thermal runaway, oscillate, burst into flames
(literally), or exhibit other forms of makes-the-owner-really-nervous
misbehavior.

So, I'd certainly recommend de-rating all resistors conservatively, to
ensure long life. Running 'em at no more than 50% of rated
dissipation would probably not be a bad thing.

As to noise, though, I don't think it's a terribly big issue in any
well-designed preamp. The primary noise source in a resistor is
thermal or Johnson noise: the noise power is proportional to absolute
temperature, and a matter of a few degrees of heating around room
temperature isn't going to make a big difference. The noise voltage
across the resistor is a function of the noise power and the
resistance... the amount of material used to make up this resistance
doesn't appear to enter into it. As long as you're using good-quality
resistors (e.g. decent metal-film ones), a 1-watter ought to have the
same amount of thermal noise as a 1/8-watter, at the same temperature.

I don't know whether the size/rating of the resistor has any effect on
the quantity of excess (non-thermal) noise, but this ought to be *way*
down in the weeds if you're using good-quality film resistors.

In short, I wouldn't worry about it.

--
Dave Platt <dplatt@radagast.org> AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

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TonyP wrote:
> "Isaac Wingfield" <isw@witzend.com> wrote in message
> news:isw-301A53.19580318052004@netnews.comcast.net...
>> The noise is not due to heating, There are two sources of noise in
>> resistors, thermal noise and "excess noise". Thermal noise is a
>> function of temperature and resistance, and nothing you (or the
>> manufacturer) can do will alter it.
>
> Saying thermal noise is not due to heating, is a bit of a misnomer.
> Sure there will always be thermal noise at any temperature above
> absolute zero, but heating will obviously increse the temperature and
> hence the noise

Long ago I was building (tubed) RIAA preamps. I had a goodly collection of
small precision wirewound resistors at my disposal, so I built a stereo
preamp made up of them. The difference in noise levels, compared to carbon
compostiion resistors, was negligable.

Some time later I was building transistorized RIAA preamps, but this time
the comparison was between carbon film resistors and deposited metal
resistors. Similar results.

Archived from groups: rec.audio.tech (More info?)

"TonyP" <TonyP@optus.net.com.au> wrote in message
news:40ab893a$0$1588$afc38c87@news.optusnet.com.au...
>
> "Arny Krueger" <arnyk@hotpop.com> wrote in message
> news:7_mdnb24x5fb_jbdRVn-sQ@comcast.com...
> > TonyP wrote:
> > > Saying thermal noise is not due to heating, is a bit of a
misnomer.
> > > Sure there will always be thermal noise at any temperature above
> > > absolute zero, but heating will obviously increse the
temperature and
> > > hence the noise
>
> > Long ago I was building (tubed) RIAA preamps. I had a goodly
collection of
> > small precision wirewound resistors at my disposal, so I built a
stereo
> > preamp made up of them. The difference in noise levels, compared
to carbon
> > compostiion resistors, was negligable.
> > Some time later I was building transistorized RIAA preamps, but
this time
> > the comparison was between carbon film resistors and deposited
metal
> > resistors. Similar results.
>
> Yes but has nothing to do with temperature. Not that I was
suggesting large
> differences, just that physics dictates an increase.
> As for the reliability of carbon resistors, put your money on the
metal :-)
> The carbon WILL become more noisy at some stage.

The thermal noise of all resistances is the same: kTB. The answer
is in watts. If there is current flowing through the resistor, there
will be additional noise, the amount and spectral charateristics of
which are wildly different. I've found that bulk metal resistors have
the least added noise, followed by metal film. The larger the
resistor, the quieter it is wrt the excess noise.

Norm Strong

Archived from groups: rec.audio.tech (More info?)

In article <7_mdnb24x5fb_jbdRVn-sQ@comcast.com>,
"Arny Krueger" <arnyk@hotpop.com> wrote:

> TonyP wrote:
> > "Isaac Wingfield" <isw@witzend.com> wrote in message
> > news:isw-301A53.19580318052004@netnews.comcast.net...
> >> The noise is not due to heating, There are two sources of noise in
> >> resistors, thermal noise and "excess noise". Thermal noise is a
> >> function of temperature and resistance, and nothing you (or the
> >> manufacturer) can do will alter it.
> >
> > Saying thermal noise is not due to heating, is a bit of a misnomer.
> > Sure there will always be thermal noise at any temperature above
> > absolute zero, but heating will obviously increse the temperature and
> > hence the noise
>
> Long ago I was building (tubed) RIAA preamps. I had a goodly collection of
> small precision wirewound resistors at my disposal, so I built a stereo
> preamp made up of them. The difference in noise levels, compared to carbon
> compostiion resistors, was negligable.

Wirewound resistors can be rather inductive, and that can make for
"interesting" stability problems.

> Some time later I was building transistorized RIAA preamps, but this time
> the comparison was between carbon film resistors and deposited metal
> resistors. Similar results.

Compared to the groove noise, I don't think anything about the resistor
matters 8^}.

IMHO, the noise level when the stylus is not in the groove is of no
concern as long as it's at least 10 dB below the in-groove value. It
doesn't take *real* low-noise technique to achieve that.

When I designed my own preamp, I selected the topology for lowest
distortion instead of lowest noise -- that meant using a long-tailed
diff pair for the front end. A single bipolar transistor running at
microamp base currents shows considerable distortion due to Rbe
modulation.

Oddball piece of information: The Rbe of a transistor is not an actual
resistance, and does not behave as one, noise-wise. This is a Good
Thing, because at very low collector currents, Rbe can be interestingly
large.

Isaac

Archived from groups: rec.audio.tech (More info?)

"Don" <TAKE-OUTdobrien25@comcast.net> wrote in message
news:uyxqc.74473$536.12094292@attbi_s03...
> Is it better to use over rated (higher wattage) resistors for low noise,
or
> just enough wattage capability to cover expected conditions plus a little
> more for safty ?
>
> My thinking is that over rating will result in cooler resistors, so
therefore,
> less noise, but, on the otherhand, more material for the signal to pass
> through, therefore, more noise.
> -Don


Check out Randall Aiken's website for an excellent technical paper on the
subject of resistor types. There's actually 3 types of resistor noise.

http://www.aikenamps.com/

Click on Tech Info, then Technical Papers Advanced, then on "Resistor
Types - Does it Matter?


Mikey

Archived from groups: rec.audio.tech (More info?)

TonyP wrote:
> "Isaac Wingfield" <isw@witzend.com> wrote in message
> news:isw-5E2E1E.20221819052004@netnews.comcast.net...
>> Compared to the groove noise, I don't think anything about the
>> resistor matters 8^}.
>
> True.
>
>> IMHO, the noise level when the stylus is not in the groove is of no
>> concern as long as it's at least 10 dB below the in-groove value. It
>> doesn't take *real* low-noise technique to achieve that.
>
> Depends on the noise, but I would want a slightly better margin than
> that, and is very easy to achieve anyway.

Agreed. You have to consider not only the over-all amplitude of the noise,
but also its spectum.

>> When I designed my own preamp, I selected the topology for lowest
>> distortion instead of lowest noise -- that meant using a long-tailed
>> diff pair for the front end. A single bipolar transistor running at
>> microamp base currents shows considerable distortion due to Rbe
>> modulation.
>
> Since the distortion on any vinyl record is also high, you are
> reducing one non-problem, whilst claiming another is of no importance.

Same basic comment as noise. The spectral content of the nonlinear
distortion have to be considered. However, it's trivial to build electronics
with nonlinear distortion that is so much less than that of the LP, that
there's not a lot to worry about.

IME, the most common audible issues relating to phono preamps relate to
frequency response, both that due to the RIAA demphasis network, and that
due to cartridge loading.

Archived from groups: rec.audio.tech (More info?)

"Arny Krueger" <arnyk@hotpop.com> wrote in message
news:vYqdnXPMztw_ZTDd4p2dnA@comcast.com...
> Same basic comment as noise. The spectral content of the nonlinear
> distortion have to be considered. However, it's trivial to build
electronics
> with nonlinear distortion that is so much less than that of the LP, that
> there's not a lot to worry about.

Agreed.

> IME, the most common audible issues relating to phono preamps relate to
> frequency response, both that due to the RIAA demphasis network, and that
> due to cartridge loading.

Cartridge loading is usually easy to fix, and IME freq response errors are
usually much less than the variation in the records themselves.
Whilst it is good practice to set up a flat system using a good test record,
the variation in response from supposedly identical records, but from
different pressings, will usually be larger than any phono pre-amps
variation from ideal RIAA response. Worrying about variations less than 1-2
dB is a waste of time IMO.

TonyP.

Archived from groups: rec.audio.tech (More info?)

"Arny Krueger" <arnyk@hotpop.com> wrote in message
news:tdWdnUrNUKgBDy3d4p2dnA@comcast.com...
> > Cartridge loading is usually easy to fix,

> But IME rarely fixed.

Yes it's amazing how many people would rather buy a new pre-amp or
cartridge, than a 10 cent capacitor :-)
I buy cartridges based mainly on tracking performance (Shure V15VMR) then
adjust loading to suit.

> > and IME freq response
> > errors are usually much less than the variation in the records
> > themselves.

> However, that doesn't let them off the hook. If they are audible then they
> represented undesirable changes in sound quality.

But how are they audible, only when doing a direct comparison with something
else?
Which then is the more accurate? How do you know? Does it matter if it
sounds good to you?

> > Worrying about variations less than 1-2 dB is a waste of time IMO.
> It very much depends where those 1-2 dB are.

Not at all, since the records frequency variation will be all over the
place. Simply adjust tone controls to taste. That's what the mastering
engineer does anyway!

> Take a listen to the differences from variation that size that you can
hear
> in musical samples you can download from
> http://www.pcabx.com/technical/dip [...] /index.htm , particularly the
> ones I call "tips".

When listening to records I don't usually ABX them to the master tapes. So I
have no idea which pressings are more accurate. Only which sound better to
me at the time.

> IME mastering is often about broad but shallow changes in frequency
> response.

As is the response variation in most pre-amps.
IME the mixing/mastering, total EQ will be *MUCH* greater overall. And not
flat to any reference whatsoever.

TonyP.

Archived from groups: rec.audio.tech (More info?)

"Arny Krueger" <arnyk@hotpop.com> wrote in message
news:IP6dnSdQi_yD2C7d4p2dnA@comcast.com...
> > But how are they audible, only when doing a direct comparison with
> > something else?
> It's often apparent without comparison.

Not sure how you would know whether it's the equipment or the record?
If they put test tones on every record you may have a shot.

> > Which then is the more accurate?
> The one you get when you get the FR of the playback equipment right.

Not necessarily. If the record has say 3dB droop at HF compared to the
master tape, then the cartridge/pre-amp with a 3dB rise will be more
accurate for that record.

> > How do you know? Does it matter if it sounds good to you?

> I find that if you get the FR of the playback equipment right, more
> different recordings sound good to me.

I already stated that you should set the response flat using a good test
record. Then you can ignore the 1-2 dB variations from RIAA that your
cartridge/pre-amp might have, safe in the knowledge that the records you
play will be far more than that anyway. Compensate with EQ as necessary.

> > Not at all, since the records frequency variation will be all over the
> place.
> Right, but I find that there is a natural centerline out there someplace.

I don't, but getting as flat as possible with a test record, is a good place
to start anyway.

> > Simply adjust tone controls to taste. That's what the mastering
> > engineer does anyway!
> It's nice to be able to play a stack of recordings without constantly
> fiddling with the gear.

Of course you can, but that doesn't mean they will all sound similar in
tone, or similar to what the mixing or mastering engineers heard. You can't
even expect that from CD's.

> > When listening to records I don't usually ABX them to the master
> > tapes. So I have no idea which pressings are more accurate. Only
> > which sound better to me at the time.

> Yes, but if you can tune the playback system so that it is closer to the
> median without adjustments, it takes less individual adjustment to sound
> right with a variety of recordings.

Of course, but that was never the argument.

> > IME the mixing/mastering, total EQ will be *MUCH* greater overall.
>
> Not necessarily. While I'm not shy about applying eq, I often make
> recordings where many tracks if not the whole mixdown has minimal or zero
> eq.

Sure, but that would be the exception, not the rule.

> > And not flat to any reference whatsoever.
> We all carry a reference around in our heads - it's the composite of
> everything we've ever heard.

Yep, and everybody's is different. To be a reference, you need a common
standard.

TonyP.

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TonyP wrote:
> "Arny Krueger" <arnyk@hotpop.com> wrote in message
> news:IP6dnSdQi_yD2C7d4p2dnA@comcast.com...
>>> But how are they audible, only when doing a direct comparison with
>>> something else?
>> It's often apparent without comparison.
>
> Not sure how you would know whether it's the equipment or the record?

Keep the equipment properly tuned up.

> If they put test tones on every record you may have a shot.

I do have a number of test records, spanning decades.

>>> Which then is the more accurate?

>> The one you get when you get the FR of the playback equipment right.

> Not necessarily. If the record has say 3dB droop at HF compared to the
> master tape,

That would be an artistic choice made by the mastering engineer.

>then the cartridge/pre-amp with a 3dB rise will be more
> accurate for that record.

That would be a FR error I seek to eliminate.

>>> How do you know? Does it matter if it sounds good to you?
>
>> I find that if you get the FR of the playback equipment right, more
>> different recordings sound good to me.

> I already stated that you should set the response flat using a good
> test record. Then you can ignore the 1-2 dB variations from RIAA that
> your cartridge/pre-amp might have, safe in the knowledge that the
> records you play will be far more than that anyway. Compensate with
> EQ as necessary.

Works for me, but I want to minimize the need for added eq.

>>> Not at all, since the records frequency variation will be all over the
>> place.

>> Right, but I find that there is a natural centerline out there
>> someplace.

> I don't, but getting as flat as possible with a test record, is a
> good place to start anyway.

We kinda-sorta agree.

>>> Simply adjust tone controls to taste. That's what the mastering
>>> engineer does anyway!

>> It's nice to be able to play a stack of recordings without constantly
>> fiddling with the gear.

> Of course you can, but that doesn't mean they will all sound similar
> in tone, or similar to what the mixing or mastering engineers heard.

I can if I presume he set up his playback system competently, and I do the
same.

> You can't even expect that from CD's.

I surely expect that from CDs.

>>> I don't usually ABX them to the master
>>> tapes. So I have no idea which pressings are more accurate. Only
>>> which sound better to me at the time.

>> Yes, but if you can tune the playback system so that it is closer to
>> the median without adjustments, it takes less individual adjustment
>> to sound right with a variety of recordings.

> Of course, but that was never the argument.

I'm happy to be in agreement. ;-)

>>> IME the mixing/mastering, total EQ will be *MUCH* greater overall.

>> Not necessarily. While I'm not shy about applying eq, I often make
>> recordings where many tracks if not the whole mixdown has minimal or
>> zero eq.

> Sure, but that would be the exception, not the rule.

As I tune up my recording setup, its getting to be more of the rule.

>>> And not flat to any reference whatsoever.
>> We all carry a reference around in our heads - it's the composite of
>> everything we've ever heard.

> Yep, and everybody's is different. To be a reference, you need a
> common standard.

Well yes, but common experiences can be the basis for an approximate ad-hoc
standard.

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"Arny Krueger" <arnyk@hotpop.com> wrote in message
news:euudnQSQo5FZ5y7dRVn-sA@comcast.com...
> > Not sure how you would know whether it's the equipment or the record?
> Keep the equipment properly tuned up.

Sure, but proves nothing by itself, without a reference for each recording.
How do you know if it's supposed to sound like that, or the cutter or
stamper is worn out?

> > If they put test tones on every record you may have a shot.
> I do have a number of test records, spanning decades.

So do I, but I prefer to listen to music myself.

> > Not necessarily. If the record has say 3dB droop at HF compared to the
> > master tape,
> That would be an artistic choice made by the mastering engineer.

Or a worn cutter, stamper, stylus. Lot's of possibilities.

> >then the cartridge/pre-amp with a 3dB rise will be more
> > accurate for that record.
> That would be a FR error I seek to eliminate.

Fair enough, I seek maximum listening enjoyment. Each to his own.

> > I already stated that you should set the response flat using a good
> > test record. Then you can ignore the 1-2 dB variations from RIAA that
> > your cartridge/pre-amp might have, safe in the knowledge that the
> > records you play will be far more than that anyway. Compensate with
> > EQ as necessary.
> Works for me, but I want to minimize the need for added eq.

No argument there, but I just smile at the people who play vinyl with all
controls flat, and think they have a sound the same as the original :-)

> > Of course you can, but that doesn't mean they will all sound similar
> > in tone, or similar to what the mixing or mastering engineers heard.
> I can if I presume he set up his playback system competently, and I do the
> same.

Were talking about vinyl here right?
(I'll ignore speakers for the sake of argument)

> > You can't even expect that from CD's.
> I surely expect that from CDs.

I won't ignore speakers and listening rooms here though. CD just eliminates
part of the corruption chain.

> > Yep, and everybody's is different. To be a reference, you need a
> > common standard.
> Well yes, but common experiences can be the basis for an approximate
ad-hoc
> standard.

Yes, well, sorta, maybe :-)

TonyP.

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Detector195@yahoo.com (Detector195) writes:
> [...]
> Where I have seen it make a difference is in something like a
> transimpedance front end for optical detection, where the resistor is
> often the dominant noise source.

What about a differential receiver or instrumentation amplifier where
you're trying to establish a given input impedance?
--
% Randy Yates % "How's life on earth?
%% Fuquay-Varina, NC % ... What is it worth?"
%%% 919-577-9882 % 'Mission (A World Record)',
%%%% <yates@ieee.org> % *A New World Record*, ELO
http://home.earthlink.net/~yatescr

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I just saw this thread and noted, by the way, prompt accurate information
from IsaacWingfield responding to the original question.

"Detector195" in news:6213f73a.0405251734.5d5d23e0@posting.google.com...
>
> . . . I took two resistors as
> "signal sources" to compare their noise spectra.
> One was a 100k 1/4 W metal film, the other was
> a 100k 1/8 W carbon film.

(Careful -- two variables changed at once. An issue of possible distraction
to some readers, more really than of misleading conclusions.)

>
> The carbon film had 6 percent more voltage noise from essentially
> zero up to 20 kHz, give or take 1 percent. This is about 0.5 dB.
> Does anybody out there have a real "professional" spectrum
> analyzer or digital scope? This should be an easy measurement
> if you have the right equipment.

Those data sound reasonable to me. Without going into details, I have done
many measurements as queried above. I use some very exquisite equipment for
low-noise measurements, some of the best available in the last few decades;
we have a lab full of it for such purposes. (By the way, you generally want
analog, or at least good-analog-front-end, instruments to measure low-freq.
noise spectra with low floors. And/or, build outboard low-noise preamps for
the purpose and keep them in the same lab.) My end applications were not
specifically audio, but I measured in the same frequency range. (I was
concerned with "making" resistors in monolithic form, and possible sources
of "excess" noise).

The whole issue here is the "excess" noise that Isaac Wingfield already
concisely explained. Typically it arises not in uniform resistive materials
but in interfaces between different materials, or between different crystals
or clusters of material. Commercial component resistors of metal or metal
film, common and fairly cheap anyway, have the general reputation of the
lowest excess noise, followed by carbon film. Carbon composition resistors
(polycrystalline I think, and very common construction for wired reasistors
when I was younger) have the worst reputation.

Issues of the power rating of a resistor are only peripherally related to
its noise sources. Self-heating capable of significantly raising a
resistor's Kelvin temperature (which is what counts) from the usual 300-350
found in operating electronic equipment would mean that the resistor is run
at a high power level, which argues independently for a higher power-capable
resistor, regardless of noise considerations. (Resistors, like people, are
most reliable when not overheated.)

I still think Isaac Wingfield said it more concisely. -- Max Hauser