Low noise surface mount resistors?

tk@halmi

Well-known member
Joined
Jun 3, 2004
Messages
999
Location
Oregon, USA
I remember discussions on this, but no matter how I searched this forum I get hits for 6000 topics every time, but no relevant post to this fact. So excuse me for the repetition.
As I recall Brad has measured several brands/models. Can anyone recall which ones came close to trough hole performance? I vaguely remember that larger surface mount resistors perfromed better.

Thank You,
Tamas
 

tk@halmi

Well-known member
Joined
Jun 3, 2004
Messages
999
Location
Oregon, USA
[quote author="Samuel Groner"]www.groupdiy.com/index.php?topic=9035
The passive components META did the trick! :wink:
Samuel[/quote]

Thank You, Samuel. I will have to look in the METAs next time too.
It doesn't seem that Brad has concluded his quest on the low noise smd resistors.

Cheers,
Tamas
 

chrissugar

Well-known member
Joined
Jun 4, 2004
Messages
1,314
Location
Romania
Hey Tamas

The name of the thread was "High 1/f noise in SM resistors" and it is here:
http://www.groupdiy.com/index.php?topic=9035
On page two, Brad posted some noise measurements for various series of resistors.

chrissugar
 

bcarso

Well-known member
Joined
Feb 20, 2005
Messages
4,055
Location
San Fernando Valley, Los Angeles
[quote author="tk@halmi"]
It doesn't seem that Brad has concluded his quest on the low noise smd resistors.

Cheers,
Tamas[/quote]

This is so. However, the MELFs are nothing more than axial metal film parts with no leads, so they are likely one reliable way to go despite the strident protests of your manufacturing folks. It looks from the Matsushita data and the claims of Vishay et al. that the thin-film SMD parts are also going to be o.k., although very expensive.
 

FredForssell

Well-known member
Joined
Jun 4, 2004
Messages
115
Location
Sandpoint, Idaho
They don't have to be expensive...

Susumu Co LTD (SSM) thin film 0.5% 0805 resistors from Digi-Key are 4 cents each in 200 quanity. I think they are nichrome film, as are the Beyschley MELF.

I use another brand's MELF resistors that use tantalum nitride film, but they must be purchased in full reel quanities (2.5k and 3k) from Japan and they take a long time to get. They are about 5 cents each in full reel quanities.

Cheers
 

Svart

Well-known member
Joined
Jun 4, 2004
Messages
5,134
Location
Atlanta GA USA
I am almost ready to start laying out a PCB for my Buss project. I initially thought of doing mostly SMD if i could help it but now I have to think twice..

Do I make this cheaper by avoiding a lot of through holes and vias and using only those I HAVE to use? Or do I just say screw it and make it all through-hole? the only parts that would be through hole would be the DOAs, Switches and Pots, if i can help it. All inductors, caps and ICs would be SMD of some form or another shrinking this PCB from 24"x6" to possibly 24"x2", maybe even shorter than 12" if I leave out a few things. that would bring my cost down considerably..

OR

I could lay out for both and just not drill the holes.

OR

Build two and compare.

BUT

Time and money are limited so I would rather choose one to start.

I'm willing to be a guinea pig for the susumu parts.
 

Rochey

Well-known member
Joined
Jul 2, 2004
Messages
2,693
Location
Dallas, TX - Formerly UK
Guys,

I fired off the question (as it was of interest to me too) to our Pro Audio Apps Engineer --- he came back with the following.


Resistors are the least of your worries for lower frequency noise.

Typically, 1/f noise from an IC amplifier or from within the ADC itself is going to dominate.

We typically use 1% or 0.1% metal film surface mount resistors (0805 sized) in and around input buffers, ADC front ends, DAC output filters, and mic pre circuits, and have found them to work well. Panasonic's are orderable from Digi-Key and I use them constantly on my EVM designs. Since I'm measuring a pretty flat noise floor from a few tens of Hz all of the way up to Nyquist, I would say that they pose no real issue, IMHO.
 

bcarso

Well-known member
Joined
Feb 20, 2005
Messages
4,055
Location
San Fernando Valley, Los Angeles
[quote author="Rochey"]Guys,

I fired off the question (as it was of interest to me too) to our Pro Audio Apps Engineer --- he came back with the following.


Resistors are the least of your worries for lower frequency noise.

Typically, 1/f noise from an IC amplifier or from within the ADC itself is going to dominate.

We typically use 1% or 0.1% metal film surface mount resistors (0805 sized) in and around input buffers, ADC front ends, DAC output filters, and mic pre circuits, and have found them to work well. Panasonic's are orderable from Digi-Key and I use them constantly on my EVM designs. Since I'm measuring a pretty flat noise floor from a few tens of Hz all of the way up to Nyquist, I would say that they pose no real issue, IMHO.
[/quote]

Humble opinion or arrogant opinion, he is neglecting the presence of d.c. (when it is present) or similar low frequency noise riding on signal swings. And, note that he is talking about metal film (i.e., I believe, thin film) resistors, not the bog-standard cheapest thick film parts. These were anything but "the least of [my] worries for lower frequency noise." :razz:

The app that brought the terrible performance of Rohm thick film parts to my attention had lots of d.c. as standing current in a discrete component front end. Audibly and measurably the noise was terrible. And I can assure your engineer that the 1/f noise from the JFET and bipolars in the circuit were negligible by comparison.

It was tamed by a combination of reducing the standing current and changing vendors (Yageo and Panasonic were both a lot better), but it never got anywhere near as good as ~1/4W standard metal-film axial parts, even with those running the higher currents. I'm sure the parts Fred F. mentions would have been much better than the Yageo/Pana parts, but they appeared to be too expensive for this very cost-sensitive design. And no board layout changes could be made by customer edict at the point these issues surfaced---no larger footprints for bigger parts (which helps) and no place to be made for axials.

The subtlety here: one could say "Well, isn't it obvious? Don't run d.c. through your resistors!" But realize that large low-frequency signal swings are tantamount to d.c. and will indeed have excess noise riding on them. If you are only concerned about passing a spec then this may be satisfactory. But at least it is something to be wary of.

See also in this connection the Gilbert article and his remarks (see Note 4 in particular) about active circuit biasing.



Note to self for future controversial threads: stochastic resonance :cool:
 

Svart

Well-known member
Joined
Jun 4, 2004
Messages
5,134
Location
Atlanta GA USA
yeesh. I really want to try SMD parts in some of my audio projects but I really don't want to waste time doing two layouts, one with SMD and another with TH parts..

I am really leaning toward trying those thin film parts mentioned earlier in the thread. Most everything else can be had SMD including the inductors and caps I plan to use. This would cut the size of the PCB and the price of the PCB down considerably.

What do you think?
 

Svart

Well-known member
Joined
Jun 4, 2004
Messages
5,134
Location
Atlanta GA USA
wow, who knew thin film parts were so EXPENSIVE.

Mouser has better prices, around .40$ EACH.

:shock:

this leaves the question, what parts NEED to be thin film? do the parts in the servo circuit need to be thinfilm? how about any in the feedback network?


I'm rethinking the through hole approach..
 

FredForssell

Well-known member
Joined
Jun 4, 2004
Messages
115
Location
Sandpoint, Idaho
As I said before...

They don't have to be expensive...

Susumu Co LTD (SSM) thin film 0.5% 0805 resistors from Digi-Key are 4 cents each in 200 quanity. I think they are nichrome film, as are the Beyschley MELF.

I do not think that $0.04/each is expensive for high quality thin film resistors... and they are 0.5% parts. I mean, that's $8 for 200 resistors. The 0.1% parts are more expensive.
 

Svart

Well-known member
Joined
Jun 4, 2004
Messages
5,134
Location
Atlanta GA USA
ah i see where you are looking now. I looked right over the .5% parts.

10 for 1.40 is not bad at all.

most every other brand they were 40 cents each, and that is what I was talking about.

I see the .5% are nichrome too.
 

FredForssell

Well-known member
Joined
Jun 4, 2004
Messages
115
Location
Sandpoint, Idaho
I see the .5% are nichrome too.

Yeah, I think that a very high percentage of thin-film resistors are going to be nichrome... at least in the SMT varity. Tantalum Nitride thin-film are FAR harder to find, and more expensive.
 

Svart

Well-known member
Joined
Jun 4, 2004
Messages
5,134
Location
Atlanta GA USA
I bought a used metcal setup for 50$ on ebay. I bought another lot of tips for 50$, mostly smd tips for soic and tqfp packages although I have perfected getting these off with a normal tip.. They cut the time needed down from several minutes to 10 seconds or so.

You will appreciate the ease of use!

the only problem with these parts is the lack of stock in 1206 size parts. I'm laying out pads that can accept both 805s and 1206s since I'd rather work with 1206(larger film area).
 

Latest posts

Top