SMD 1206 VS 0805 resistors

Hi,

It is quite difficult to find 1206 chip resistors at reasonable prices... neither farnell, mouser, Rs,  but 0805, hey!.. very easy to find good prices at farnell or other distributors. So, for audio projects..¿are 0805 smd ok?  ...they are 1/8 watt instead of the usual 1/4 watt... ¿does it make big difference? The circuits i'm working on will draw about 40 ma, from a 6va power supply. I have opened an old TC M300 multieffects recently... and it is stuffed with  smd parts smaller than 0805...so in theory 0805 parts could be ok for typical opamp audio circuits.

Thanks  for your advise!
JAY X

in digital electronics, there's virtually no difference, as most stuff is running at low voltage.

In analog electronics - keep an eye on things.

- Carbon vs. Thick Film vs. Thin film resistors
- Resistor Voltage Coefficients (higher the voltage across the resistors, the more the resistance can vary, causing distortion <- typically caused my instantaneous heating of the resistor).
- Voltage rating of the cap - the smaller the physical size of the cap, the harder it is to get a high voltage and high F device.

Good luck

/R

Hi Rochey,

Yes.. I forgot to mention: Analog design, only opamps  LM833P, INA137/DRV134... 1% THIN FILM resistors 50PPM 125mw...
¿0805? like these: http://es.farnell.com/yageo-phycomp/rt0805fre071k5l/resistencia-0805-1-50ppm-1k5/dp/1500678

That is the question...
JAY X

whats the voltage swing? how good is "good enough" ?

I don't like generalizing but there are issues with too small resistors for precision audio paths. Look into the voltage coefficient specifically.

For non-premium paths I routinely use resistor arrays, but I don't listen to the audio frequencies I crunch. 

JR

Hi,

The dual supply voltage is +/-18v...so 36 v voltage swing..

I also thought to use minimelf resistors..0204...

And good enough would mean as good as a thru hole 1/4w 1% metal film resistor.

JAY X

Try mini-melf metal oxide resistors..

Again look at the data sheets, or perform your own experiments. Guys I know doing consoles do their own testing. In my opinion you should not be able to measure your resistors with a distortion analyzer.

JR

PS: 0204 parts should not exist for multiple reasons.  8)  They're too damn small.

You need to confer the resistance value for the resistor too... Dumping 18v into a 100ohm resistor will cause instantanios heating

You can parallel several m/ox mini-milfs and get close to TH vibe.

Perhaps not so practical for a factory run, but for a home-brew 1337 boutique-vibe apparatus, this is the ticket.

JAY X said:

I also thought to use minimelf resistors..0204...

Click to expand...

I can't SEE 0204 resistors - hence they do not exist
M

Hi,

I also found, realize, that 0207 MELF, bigger, are easier to layout, their body size is simmilar to a thru-hole part.

Most datasheets show Voltage rating and temperature coefficient, But not voltage coefficient, maybe i'm confusing terms...

JAY X

http://www.yageo.com/portal/product/product.jsp?NEXT_PAGE=/product/categorySearch.jsp&SWITCH_CATEGORY=/product/LeadedR/Melf%20Metal%20Film

If I worked in a marketing dept., I might say something like "built for rock".. or something of equal artificial sweetnes.

Hmm... VIVA LE MILF RESISTANCE

JAY X said:

Hi,

I also found, realize, that 0207 MELF, bigger, are easier to layout, their body size is simmilar to a thru-hole part.

Most datasheets show Voltage rating and temperature coefficient, But not voltage coefficient, maybe i'm confusing terms...

JAY X

Click to expand...

Voltage coefficient will actually cause distortion as the resistance changes directly with terminal voltage. For very small (low mass) parts it's possible to see distortion from temperature changing with signal due to simple power dissipation.

Like I mentioned some design engineer do their own testing, that is the real bottom line. How do the parts work in a given application. This can make a large difference with caps in actual filters, but again for onesy twosey DIY, buy premium, but not silly expensive, parts.

JR

Hi everybody!

Once decided to go SMD, SOIC8W, 1206, and melf0207....I'm thinking to use hot air with low speed flow to solder smd... a stencil to diposit the solder paste, and then solder by hot air and/or reflow on a hot plate...

¿has anyone experience on the process?

JAY X

Search for expat audio videos on YouTube... ILoVE the SMd manufacturing process.

JAY X said:

Hi everybody!

Once decided to go SMD, SOIC8W, 1206, and melf0207....I'm thinking to use hot air with low speed flow to solder smd... a stencil to diposit the solder paste, and then solder by hot air and/or reflow on a hot plate...

¿has anyone experience on the process?

JAY X

Click to expand...

I have a fair amount of experience professionally.  Use high quality paste and do a few test runs.  The stencil process alone is a challenge and each step afterward only gets more complex.  I wouldn't recommend a hot plate as it is vet easy to burn your board but I do understand the desire to not blow your parts all over the place.  Solder paste has a specific reflow profile that you should follow.  I've seen people diy reflow ovens which is a lot of work but pays dividends if you are trying to produce any kind of volume. 

I've managed to do a lot of boards with a hot air wand. (a proper smd rework tool). They can be had on ebay for less than $100.
I've also done a lot with a reflow skillet, but I'm starting to wander away from that.

One of these days, I'll invest in a proper reflow oven, but as I have a working solution, that can wait.

/R

I have spent much time evaluating various resistor technologies/sizes recently. I have not evaluated 0805 resistors in detail, but what I can say is that thin film 1206 0.1% 25 ppm parts are, generally speaking, clearly inferior to thin/metal film (not metal oxide as mentioned in an earlier post!) MiniMELF (0204) 1% 50 ppm. That's both with respect to distortion from power and voltage coefficient.

Samuel