Sea Urchin caps

[muddyfox]

Hello all!

I'm trying to drink the DipTrace Koolaid and at the same time get my feet wet with smd.
My question is which of the electrolytes on sea urchin can be replaced with non-electrolytes? I have both but I find 0805's somewhat easier to solder so I'd like to go with those if at all possible.
Or to put it another way, which electrolytes are necessary? Power filtering near the 7805? Output? The one on the pt2399?

[alanp]

Electro's are a bit of a compromise, as they're usually used where film type caps in the value required would be horribly huge. (with the trade-off that electros dry out over time, and they have polarity which is not good but can be lived with.)

If you can find 0805 caps in the values required, you should be okay for substitutions. Tayda only sell up to 470uF, though.

[rullywowr]

Hello all!

I'm trying to drink the DipTrace Koolaid and at the same time get my feet wet with smd.
My question is which of the electrolytes on sea urchin can be replaced with non-electrolytes? I have both but I find 0805's somewhat easier to solder so I'd like to go with those if at all possible.
Or to put it another way, which electrolytes are necessary? Power filtering near the 7805? Output? The one on the pt2399?

That's great you are getting along with Diptrace...I love it!

Sounds like you are doing a SMD layout, nice!  I would suggest replacing the electros (1uF and 47uF) with tantalum caps.  These are available in SMD and have a smaller footprint than electros.  They are also polarized just like the electros and will work the same.  Try to settle on a case size first then you can choose the footprint you want to use.  They are usually a size like 1206 or sometimes also referred to as "B" case or "C" case etc.  The closer the letter is to "A", the smaller they are.  Of course, you could also just use electro SMDs or even do a hybrid layout with through-hole SMD electros.  It's up to you.

Check out wikipedia for a quick crash course in SMD capacitor case sizes under "Surface Mount Technology" article.

[muddyfox]

Thanks folks! I was really just making sure that there's no some redeeming quality to electros that makes them the best choice for a particular application (say power filtering) other than price/size/availability.

@Rully: yeah, I figured if I was gonna go with this smd thing that I was gonna go all the way. No th (other than wires and board-mounted pots). Makes me feel like I'm back to square one as my th stash is no help and whatever I need I need to source from China again. 

[pickdropper]

I've done an SMD version of the Sea Urchin.

You can use 0805s for MOST of the caps.  You are probably going to need to use a Tantalum for the 100uF.  I don't know of any 0805 in that size and voltage.

For the 47uF caps, you can get an 0805 cap for the one that goes after the 5V regulator, but they only go up to 10V.

I usually put 25V 1206 caps for the 47uF.  If you are ordering some for the dual fuzz board, you can get some extra and use 2 of that same cap in the Sea Urchin.

[muddyfox]

Thanks Pick!

I've resigned to using smd electrolytes (there are 8 of them, space hoggers) for my v1 build (still testing Diptrace waters), but good to know.

[pickdropper]

I highly recommend using tantalum over SMT electros.  They fit a lot better in smaller enclosures.  They are also more reliable long term.  The downside is that they are more expensive.

[muddyfox]

I'd love to but I'm simply unable to find a decent source that doesn't cost an arm and a leg. I already have some electros, it'd be a shame to trash them, especially since I only build for myself and don't need to rely on their longevity.
Duly noted, though. I'll stock up on tants as soon as I find a reasonable supplier. Chromesphere, are you listening? How 'bout a smd tant kit? 

[muddyfox]

I highly recommend using tantalum over SMT electros.  They fit a lot better in smaller enclosures.  They are also more reliable long term.  The downside is that they are more expensive.

Pick, about replacing electros with tants... Normally I don't use <25V rated caps, just to be on the safe side. The best I can find on tants are 16V. Is this a problem in normal 9V pedal application? Are tants more sturdy than electros when push comes to shove?

[pickdropper]

16v caps in a 9v application is generally considered enough safety margin to be acceptable.  I wouldn't use 16v caps in applications that use a 15v power supply , however.

[muddyfox]

Gotcha!

I was thinking of grabbing these to replace my smd electros?

http://www.ebay.com/itm/100-PCS-1UF-16V-3216-18-SMA-Tantalum-capacitor-105-/121215487564?pt=LH_DefaultDomain_0&hash=item1c39018e4c

http://www.ebay.com/itm/50-PCS-100UF-16V-7343-31-SIZE-D-SMD-Tantalum-capacitor-SMT-NEW-/370943441135?pt=LH_DefaultDomain_0&hash=item565df3b8ef

[pickdropper]

Gotcha!

I was thinking of grabbing these to replace my smd electros?

http://www.ebay.com/itm/100-PCS-1UF-16V-3216-18-SMA-Tantalum-capacitor-105-/121215487564?pt=LH_DefaultDomain_0&hash=item1c39018e4c

http://www.ebay.com/itm/50-PCS-100UF-16V-7343-31-SIZE-D-SMD-Tantalum-capacitor-SMT-NEW-/370943441135?pt=LH_DefaultDomain_0&hash=item565df3b8ef

For the 1uF, I would probably use 0805 ceramics.  They are a LOT smaller.  You can easily get them in the voltages you want.

For the 100uF, those will work fine.  Make sure your layout uses the correct package size.  I usually use the smaller 'C' package size, but they are admittedly a bit harder to find.  Size 'D' are more common for 100uF caps.

[muddyfox]

Yeah I just checked the listing for the same 0805 ceramic kit I got and it has 1u in x7r and 2u2 in y5v.

So for 10u and above (mostly 47 and 100 methinks) I'm gonna go with 16v tants. Thanks!!

[pickdropper]

x7r are nice caps and about the best you are going to do with 1uF. 

y5v caps are pretty bad and I generally avoid them whenever possible.  They are like the really cheap ceramic disc caps.  They vary greatly with heat and their capacitance drops if you use them close to their rated voltage.  They'll work OK in most circuits, but the sound may be a bit different if the capacitance drops.

[muddyfox]

For the 47uF caps, you can get an 0805 cap for the one that goes after the 5V regulator, but they only go up to 10V.

I was just re-reading this and was wondering... since everything after the regulator is 5V anyways, wouldn't 10V be enough?
E.g. the 47u on pt2399 pin2 and 1u before the feedback pot and 1u on mix pot wiper etc? Does any of these places ever get a voltage that's >5V?