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OT 0805 resistor noise

  • Thread starter martin griffith
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M

martin griffith

Jan 1, 1970
0
I've been looking spec for resistors, rather boring, but what's the
difference between thick film and thin film noise, the data sheets are
not very forthcoming

It seems that thick film are noisier, so I started looking for 1%
thin film stuff (for audio), but although they seem to be available
all the distro's, Digikey/farnell just seem to stock .1% types, a bit
excessive for audio purposes in most cases, the only exception would
be RIAA EQ (joke)


martin
 
W

Winfield Hill

Jan 1, 1970
0
martin griffith wrote...
I've been looking spec for resistors, rather boring, but what's the
difference between thick film and thin film noise, the data sheets
are not very forthcoming.

It seems that thick film are noisier, so I started looking for 1%
thin film stuff (for audio), but although they seem to be available
all the distro's, Digikey/farnell just seem to stock 0.1% types, a
bit excessive for audio purposes in most cases, the only exception
would be RIAA EQ (joke).

Some of the old carbon-composition resistors suffered from "excess
noise," which was noise above the Johnson-noise formula, under the
condition of a substantial current flowing through the resistor
(i.e., a substantial voltage across the resistor). A Google search
shows rumors of excess noise for (some) thick-film resistors, and
perhaps less so, for some thin-film resistors... At any rate, this
should be an easy parameter to measure, if indeed it exists. I've
made modest efforts to take such measurements from time-to-time in
the last few years, hoping to see something, but I've not actually
observed any excess noise with modern parts. Perhaps I was trying
the wrong brands, or the wrong resistance values?
 
J

John Larkin

Jan 1, 1970
0
I've been looking spec for resistors, rather boring, but what's the
difference between thick film and thin film noise, the data sheets are
not very forthcoming

It seems that thick film are noisier, so I started looking for 1%
thin film stuff (for audio), but although they seem to be available
all the distro's, Digikey/farnell just seem to stock .1% types, a bit
excessive for audio purposes in most cases, the only exception would
be RIAA EQ (joke)


martin

All resistor types have the same Johnson noise, the spontaneous noise
that you see with no bias. If DC is flowing, you get added shot noise.
Metal-film (thin-film) resistors are supposed to have less shot noise
for quantum-mechanical reasons; Phil Hobbs has commented on this here
and in his book.

Some really nasty old carbon resistors have excess noise, as Win
notes.

So, use low-value metal-film resistors and don't have DC across them
if you can help it.

John
 
M

martin griffith

Jan 1, 1970
0
martin griffith wrote...

Some of the old carbon-composition resistors suffered from "excess
noise," which was noise above the Johnson-noise formula, under the
condition of a substantial current flowing through the resistor
(i.e., a substantial voltage across the resistor). A Google search
shows rumors of excess noise for (some) thick-film resistors, and
perhaps less so, for some thin-film resistors... At any rate, this
should be an easy parameter to measure, if indeed it exists. I've
made modest efforts to take such measurements from time-to-time in
the last few years, hoping to see something, but I've not actually
observed any excess noise with modern parts. Perhaps I was trying
the wrong brands, or the wrong resistance values?

Thanks Win, I'll just go with the cheapo ones.

BTW . All audio circuits use 600R, 4K7 and 10K, nothing else, ever,
honest.


martin
 
T

Terry Given

Jan 1, 1970
0
John said:
All resistor types have the same Johnson noise, the spontaneous noise
that you see with no bias. If DC is flowing, you get added shot noise.
Metal-film (thin-film) resistors are supposed to have less shot noise
for quantum-mechanical reasons; Phil Hobbs has commented on this here
and in his book.

which book was that?
Some really nasty old carbon resistors have excess noise, as Win
notes.

So, use low-value metal-film resistors and don't have DC across them
if you can help it.

John

Cheers
Terry
 
P

Pooh Bear

Jan 1, 1970
0
John said:
All resistor types have the same Johnson noise, the spontaneous noise
that you see with no bias. If DC is flowing, you get added shot noise.
Metal-film (thin-film) resistors are supposed to have less shot noise
for quantum-mechanical reasons; Phil Hobbs has commented on this here
and in his book.

Some really nasty old carbon resistors have excess noise, as Win
notes.

So, use low-value metal-film resistors and don't have DC across them
if you can help it.

They're not 0805s but ISTR that metal oxide ressitors are the quietest of
the lot typically.

Graham
 
P

Pooh Bear

Jan 1, 1970
0
martin said:
I've been looking spec for resistors, rather boring, but what's the
difference between thick film and thin film noise, the data sheets are
not very forthcoming

It seems that thick film are noisier, so I started looking for 1%
thin film stuff (for audio), but although they seem to be available
all the distro's, Digikey/farnell just seem to stock .1% types, a bit
excessive for audio purposes in most cases, the only exception would
be RIAA EQ (joke)

Joke assimilated ! ;-)

I don't attempt to use 0805 types for low noise. I switch to leaded types
where necessary.

Then again I'm now moving back away from SMD for the most part.

Graham
 
J

John Larkin

Jan 1, 1970
0
which book was that?

"Building Electro-Optical Systems: Making it all Work"

Excellent stuff, but somewhat more electro-optics than pure
electronics.

John
 
M

martin griffith

Jan 1, 1970
0
Joke assimilated ! ;-)

I don't attempt to use 0805 types for low noise. I switch to leaded types
where necessary.

Then again I'm now moving back away from SMD for the most part.

Graham
One of the few graphs I found was
http://www.farnell.com/datasheets/6372.pdf
page 2, shows that the smaller body R has more noise.



martin
 
P

Pooh Bear

Jan 1, 1970
0
Walter said:
Pooh Bear said:
[...]
Then again I'm now moving back away from SMD for the most part.

How come?

I thought that might raise a few eyebrows !

Several reasons actually. Here's a few.

First off - it's clear that SMT is great for large scale high quantity
manufacturing. It involves quite a high investment in tooling, jigs etc
for a product made that way to make sense though and the big economies
only really result when a line can be set up to run full tilt for a
while.

We tend to make products in rather more modest quantities - hundreds per
run rather than thousands. That simply doesn't make sense for SMT.

Also, many key components we use are only available in 'conventional'
technology anyway so there's quite a large amount of leaded components in
any event.

Bench serviceabilty is greater for the product using non SMT. We have
many customers ( or their techs ) who'll open up a product and fix it
themselves once it's out of warranty. They're unlikely to be able to do
that with SMT. We gain from offering a service friendly product. In
comparison other brands at the entry level in our sector are frankly now
making products that make more sense to throw away than repair.

I'm also looking ahead to lead-free. That's going to make pcb processing
so much more critical and especially so for SMT. We don't have the size
of runs to muck around playing with temperature profiles to make the
soldering reliable.

Graham
 
R

Roger Hamlett

Jan 1, 1970
0
Pooh Bear said:
Walter said:
Pooh Bear said:
[...]
Then again I'm now moving back away from SMD for the most part.

How come?

I thought that might raise a few eyebrows !

Several reasons actually. Here's a few.

First off - it's clear that SMT is great for large scale high quantity
manufacturing. It involves quite a high investment in tooling, jigs etc
for a product made that way to make sense though and the big economies
only really result when a line can be set up to run full tilt for a
while.

We tend to make products in rather more modest quantities - hundreds per
run rather than thousands. That simply doesn't make sense for SMT.

Also, many key components we use are only available in 'conventional'
technology anyway so there's quite a large amount of leaded components
in
any event.

Bench serviceabilty is greater for the product using non SMT. We have
many customers ( or their techs ) who'll open up a product and fix it
themselves once it's out of warranty. They're unlikely to be able to do
that with SMT. We gain from offering a service friendly product. In
comparison other brands at the entry level in our sector are frankly now
making products that make more sense to throw away than repair.

I'm also looking ahead to lead-free. That's going to make pcb processing
so much more critical and especially so for SMT. We don't have the size
of runs to muck around playing with temperature profiles to make the
soldering reliable.
We had exactly the same sort of 'loop' in system useage. Some time ago, I
was tending to work on products where large runs were the 'norm', and
basially went SMT. On the current products though, the volumes involved
are smaller, and savings almost non-existent. The big problem though is
that some of the kit goes into remote, enviroments, where servicing is
needed, without having to send back to the UK for a new board. By
deliberately keeping component types low (which in some cases 'costs'
extra in real estate), the units become far more field seviceable. An
engineer in the middle of India or China, can carry a relatively small kit
of parts, and have a good chance to service the equipment 'on site'. We
are now using technology, that looks 'old fashioned', but with design for
service (test points, diagnostics in the processors etc.), can be kept
running much more easily. The savings even work in less remote enviroments
(engineers in the middle of the US, and in Europe etc., can do the same).
In many cases, the kit can even become 'self diagnostic', sending with
it's recorded data, information on any errant behaviour.
There is a very big difference in this regard between 'consumer'
electronics where cost per unit is the key priority, and industrial
electronics, where the ability to keep equipment running 24/7 is the
winning formula.

Best Wishes
 
S

SioL

Jan 1, 1970
0
Pooh Bear said:
We tend to make products in rather more modest quantities - hundreds per
run rather than thousands. That simply doesn't make sense for SMT.

I second that. It makes perfect sense even for a couple hundred.
Also, many key components we use are only available in 'conventional'
technology anyway so there's quite a large amount of leaded components in
any event.

Depends on the component type. Many only come in SMT nowadays.
Bench serviceabilty is greater for the product using non SMT. We have
many customers ( or their techs ) who'll open up a product and fix it
themselves once it's out of warranty. They're unlikely to be able to do
that with SMT. We gain from offering a service friendly product. In
comparison other brands at the entry level in our sector are frankly now
making products that make more sense to throw away than repair.

Agree here.
I'm also looking ahead to lead-free. That's going to make pcb processing
so much more critical and especially so for SMT. We don't have the size
of runs to muck around playing with temperature profiles to make the
soldering reliable.

Just outsource it, they know the profiles and have plenty experience.
 
P

Phil Allison

Jan 1, 1970
0
"martin griffith"
One of the few graphs I found was
http://www.farnell.com/datasheets/6372.pdf
page 2, shows that the smaller body R has more noise.


** Beware of the realities here:

ALL equal value resistors have the same (ie Johnson only ) noise when there
is no or only low DC volts across them.

Only those resistors in a high gain input stage can possibly affect the
overall noise level and ONLY if you place lots of DC across them - this
means resistors used in typical op-amp audio circuits are never an issue.

For example:

A 10kohm resistor has 1.7 uV of Johnson noise in a 20 kHz bandwidth and 3.8
uV in a 100 kHz one - to get the "excess noise" to become significant
requires at least a 30 volts DC bias.





.......... Phil
 
P

Pooh Bear

Jan 1, 1970
0
SioL said:
I second that. It makes perfect sense even for a couple hundred.


Depends on the component type. Many only come in SMT nowadays.

In our case a heck of a lot of componentts *have* to be through hole.

I can only actually think of 3 parts we use ( DSP, ADC and DAC ) that are only available in SMT.
Agree here.


Just outsource it, they know the profiles and have plenty experience.

I don't know anyone with lead-free experience ! Since many key components are still not RoHS compliant you
can't even do any meaningful test runs.

I've seen one site using very simple 'homebrew' SMT assembly where the extra temp for lead free that they're
experimenting with results in melting some components !

And we do actually outsource btw. Only one of them does full SMT currently though and they're the ones who want
the large orders.

Graham
 
P

Phil Allison

Jan 1, 1970
0
Some Lying Pommy
And we do actually outsource btw. Only one of them does full SMT currently
though and they're the ones who want
the large orders.


** Quit this megolamanic " we" crapology.

Graham Stevenson is an unemployed wannabe.





........... Phil
 
W

Winfield Hill

Jan 1, 1970
0
John Larkin wrote...
All resistor types have the same Johnson noise, the spontaneous noise
that you see with no bias. If DC is flowing, you get added shot noise.
Metal-film (thin-film) resistors are supposed to have less shot noise
for quantum-mechanical reasons; Phil Hobbs has commented on this here
and in his book.

Some really nasty old carbon resistors have excess noise, as Win
notes. So, use low-value metal-film resistors and don't have DC
across them if you can help it.

Current flow that originates from a voltage difference across an
electrical conductor does not have shot noise. This includes all
types of resistors, not just film types. Note, a diode junction
is not a conductor for purposes of this statement.

If one has a shot-noise current source signal, such as photo-
diode current, and uses a resistor to measure this current, the
Johnson noise from the resistor will be less than the signal shot
noise if the voltage drop exceeds ~ 50mV. This can be seen by
comparing the Johnson noise power 4kT/R to the signal shot noise
2qI, and getting I*R = 2 kT/q = 2 Vt = 50mV at room temp. This
little observation would not be possible if resistors had their
own shot noise. The excess noise exhibited by some types of
resistors at high voltages is another matter, of course.
 
W

Winfield Hill

Jan 1, 1970
0
martin griffith wrote...
BTW. All audio circuits use 600R, 4K7 and 10K, nothing else,
ever, honest.

600 ohms? Not 620 or 602 ohms?
 
S

SioL

Jan 1, 1970
0
Pooh Bear said:
I don't know anyone with lead-free experience ! Since many key components are still not RoHS compliant you
can't even do any meaningful test runs.

By the time it becomes mandatory or shortly afterwards they will.
RoHS is probably a load of crap anyway, but we're stuck with it for now.

Siol
 
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