Head-Fi.org › Forums › Misc.-Category Forums › DIY (Do-It-Yourself) Discussions › SMT resistors 4 chip amp....best?
New Posts  All Forums:Forum Nav:

SMT resistors 4 chip amp....best?

post #1 of 11
1/7/10 at 9:30pm
Thread Starter 
Just getting started building an op-amp based headphone amp.

Did a bit of research on what resistors are best, and I came up with a lot of info ( albeit from years ago.... ) on through hole resistors, but not a whole lot of info on SMT style.

The board I have disigned ( lots of hours to get it "just right" ) is designed for 1206 sized 1/4w resistors. This is an issue because the only metal film resistors i can find are of the 1210 size, and very limmited ohm range.

So.... has anyone got advice for a premium sounding (and priced within reason) resistor?

I have found a couple that look good, some Vishay thin film with a low temp-coef, and some tamtalum that are symilar. These are roughly $.70 each so not too bad there.

Is there a suplier who offers a 0204 ( i think?? ) sized MELF that is a more audio freindly composition, i.e. carbon or metal film? that sized MELF (if I remember it right) would still fit the 1206 pads on the board.

Thanks, Joe
Reply
post #2 of 11
1/7/10 at 9:40pm
Thread Starter 
.... or does it even matter with a low current opamp?????
Reply
post #3 of 11
1/8/10 at 4:24am
I strongly sugest to change your pads to accept 0805 or even 0603 resistors. These are industry standard sizes and it will be much easier to find appropriate resistors.
These sizes are still very easy to solder (even though you probably will be anxious because of the size - but I learned soldering them in just some attempts).
Eg. the Vishay PLT series are 0,05% at 5ppm temperature coefficient (and expensive).
I am too very interested in finding GOOD SMT resistors - so what is important besides precision and TCR?
Reply
post #4 of 11
1/8/10 at 3:10pm
power handeling can be an issue as you go down in size - even low TC should be ran at a small fraction of their rated power
Reply
post #5 of 11
1/8/10 at 4:21pm
what resistance range are you after? I too would recommend changing to 0603 or 0805 for a larger range, but depending on how much resistance you are needing at a maximum you can get the texas components/vishay ZFoil SMD for the most highly matched and stable R I know of. bit pricey, but wow!!
Attachment 24449 the larger sizes you can get between 1206 = 10R - 25K and the largest 2512 10R-125K
0.01% tolerance and 0.1ppm/V
they make some resistor dividers and networks with the same stuff for passive rail splitting etc. I buy them direct, but google it, pretty sure there are a couple of suppliers. making a whole amp with them could get pricey, but if you choose some critical position and use them the results will be spectacular IMO who says SMD doesnt get way cool (and slightly esoteric even )
other than that the vishay thin film are a great option IMO
LL
Reply
post #6 of 11
1/8/10 at 4:45pm
VSM is okay if you have a reflow oven. The data sheet specifically states to avoid hand soldering irons.
Reply
post #7 of 11
1/8/10 at 5:13pm
really, ok well the guys at TX didnt mention it, but I suppose they expected me to read the manual. looks like i'll be changing my order or borrowing the use of an oven for my dac. first project with any number of them. thats odd, regular ZFoil R's are fine with an iron, even naked ones, so I guess it must be to do with the 'leads' or dielectric.

think I might ask Janet about that one. can access a hot air station so maybe that will do. I ordered them based on spec and my experience with TX2575 and other Zfoil R's. didnt think to read the datasheet through, just looked at spec
Reply
post #8 of 11
1/8/10 at 5:22pm
lol, it also suggests the use of a vacuum pick-up tool instead of tweezers. try that with 0805 I assume they are talking about robots

I think it could be done with a fine tip and apply solder to the pad rather than the R itself. thats how I do it anyway with small smd caps etc because otherwise it can come away stuck to the tip if you havent got a really form grip on it. i'll confirm anyway

or the perfect opportunity to try out toaster oven reflow
Reply
post #9 of 11
1/9/10 at 9:09am
What do you think about the Panasonic ERA series?
10 to 100ppm, 0402 to 1206, and a number of wattages?

Of course not as good as the Vishay above - but at least in a reasonable priced range.
Reply
post #10 of 11
1/9/10 at 5:05pm
Thread Starter 
Quote:
what resistance range are you after? I too would recommend changing to 0603 or 0805 for a larger range, but depending on how much resistance you are needing at a maximum you can get the texas components/vishay ZFoil SMD for the most highly matched and stable R I know of. bit pricey, but wow!!
Attachment 24449 the larger sizes you can get between 1206 = 10R - 25K and the largest 2512 10R-125K
0.01% tolerance and 0.1ppm/V
Good info, I had originally used 0805 sized in my layout but changed it due to wattage concern. 0805 is generally .125w and i wanted to stay .250w. I know this is overkill but i have read several places that it is good practice in amps to use larger than needed (watt wise) resistors.

But the 0805 are smaller (I prefer SMT soldering and small doesn't scare me to much ) and would be better for the layout, I could just double the resistance and stack them to get the wattage up
thanks for the advice guys.
Reply
post #11 of 11
1/10/10 at 11:49pm
You're better off leaving the pads on the board sized for 1206 parts... You can solder 0402/0603/0805 to a 1206 pad, but you can't put a 1206 part on one of the smaller pads (not easily, at least). If you want to do some tricks with your layout, you can also run smaller traces in between the pads on a single 1206 chip, which is harder to do with the smaller footprints. Just to be clear, the sizing goes (from largest to smallest):
1206, 0805, 0603, 0402, 0201

I don't suggest 0402 (and definitely not 0201) for DIY, as you'll need really fine-tipped tweezers, and sometimes it can be a pain soldering them down with a standard-sized soldering iron tip.

As far as resistor composition, i really doubt you'll be able to tell a difference. I would go with standard thick film resistors... Your semiconductor components will likely introduce more noise into your circuit than the resistors will.
Reply
New Posts  All Forums:Forum Nav:
  Return Home
Head-Fi.org › Forums › Misc.-Category Forums › DIY (Do-It-Yourself) Discussions › SMT resistors 4 chip amp....best?