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my DAC design - pup1 DAC - Page 42

post #616 of 674
Quote:
Originally Posted by tomb View Post

Quote:
Originally Posted by scootsit View Post


Great, thanks! I figured as much and just built it anyway. All the SMT stuff is done, just scrubbed the hell out of it with alcohol. It's weird that the OPA2835 can't even be in humid environments before being soldered, but after it can be submerged. I guess something would crack with the heat. Anyway, I used the solder paste and basically stuck each piece in it, then used the iron to heat it. The result is that you can have the iron in one hand and the tweezers in the other, no need to hold any solder, so you can make sure each piece lines up perfectly.

Actually, this has been the recommended method since day 1 - without solder paste.  You apply the solder to a single pad, first.  The you re-melt it with the iron in one hand and place the part with tweezers in the other hand.  That's fundamental with manual SMD soldering. wink.gif


I know, and that's how I've always done it, but I've found it a little hard to line up and get it to stay in place. Anyway, the paste just really flowed easily and allowed for repositioning while I soldered. Also, the paste holds the piece in place. Imagine sort of pushing each component into a soft clay or something. While the flux is, in and of itself, sticky this is a little different.

post #617 of 674
Quote:
Originally Posted by scootsit View Post


I know, and that's how I've always done it, but I've found it a little hard to line up and get it to stay in place. Anyway, the paste just really flowed easily and allowed for repositioning while I soldered. Also, the paste holds the piece in place. Imagine sort of pushing each component into a soft clay or something. While the flux is, in and of itself, sticky this is a little different.

There's nothing that stops you from re-positioning a part without solder paste.  That was just my point.  You apply solder to one pad - whether it's a PCM chip or just an 805/1206 cap or resistor.  Then you can walk away, have a coke or a beer, watch a movie, wake up the next day, whatever.

 

All you need to do the next time you work on it is hold the prospective part with tweezers in one hand while melting the solder on that pad with the soldering iron in your other.  There's no limit to how many times you can re-heat the one pad and then re-position the part.  In fact, what causes grief is thinking that once placed and the solder cooled, you can't do anything about it.  That's not true, at least with regular solder wire and a flux pen or flux paste.  Anyway, it's better to go ahead and re-melt the solder again and re-position the part for however many times it takes - until you get it right.  Once anchored, you can then solder the other pads (or pins if it's an IC chip) without much worry.  No extra solder involved.

 

I just didn't want anyone misled and let them think they had to have three hands to solder SMD.  That's not the case. wink.gif

 

P.S. A good flux pen almost does the same thing as you describe - the stuff is a lot like glue if you let it sit for awhile.

post #618 of 674
Quote:
Originally Posted by tomb View Post

Quote:
Originally Posted by scootsit View Post


I know, and that's how I've always done it, but I've found it a little hard to line up and get it to stay in place. Anyway, the paste just really flowed easily and allowed for repositioning while I soldered. Also, the paste holds the piece in place. Imagine sort of pushing each component into a soft clay or something. While the flux is, in and of itself, sticky this is a little different.

There's nothing that stops you from re-positioning a part without solder paste.  That was just my point.  You apply solder to one pad - whether it's a PCM chip or just an 805/1206 cap or resistor.  Then you can walk away, have a coke or a beer, watch a movie, wake up the next day, whatever.

 

All you need to do the next time you work on it is hold the prospective part with tweezers in one hand while melting the solder on that pad with the soldering iron in your other.  There's no limit to how many times you can re-heat the one pad and then re-position the part.  In fact, what causes grief is thinking that once placed and the solder cooled, you can't do anything about it.  That's not true, at least with regular solder wire and a flux pen or flux paste.  Anyway, it's better to go ahead and re-melt the solder again and re-position the part for however many times it takes - until you get it right.  Once anchored, you can then solder the other pads (or pins if it's an IC chip) without much worry.  No extra solder involved.

 

I just didn't want anyone misled and let them think they had to have three hands to solder SMD.  That's not the case. wink.gif

 

P.S. A good flux pen almost does the same thing as you describe - the stuff is a lot like glue if you let it sit for awhile.


Yes. Everything you just said is correct. In fact, I think my problem is that I always solder both sides too quickly. Also, I finally got the flux pen you recommended, it's great. The one that mouser ships via USPS, the 952, I think, it's the no clean, low solids one. Anyway, that one doesn't really work well, it's not sticky. The one you recommend is awesome.

 

No, you don't need 3 hands at all, I'm just incompetent! I don't know why I am so bad at this, but I am.

post #619 of 674

Following your discussion about repositioning, I've just found out about this great book on Dave's EEV blog. Everything you need to know about SMDs. It seems quite complete on every aspects you have to know!!

 

http://www.amazon.com/gp/product/1907920129/ref=oh_details_o00_s00_i00

 

Just ordered it from Amazon.com second hand. It's just been released and covers all techniques and concepts. You can get it with 4 SMD projects kit. It seems quite nice. Check out the review on Daves' blog. I think it's his January mailbag review. If you don't know this blog yet, then you are up for a night streaming...

post #620 of 674
Quote:
Originally Posted by scootsit View Post


Yes. Everything you just said is correct. In fact, I think my problem is that I always solder both sides too quickly. Also, I finally got the flux pen you recommended, it's great. The one that mouser ships via USPS, the 952, I think, it's the no clean, low solids one. Anyway, that one doesn't really work well, it's not sticky. The one you recommend is awesome.

 

No, you don't need 3 hands at all, I'm just incompetent! I don't know why I am so bad at this, but I am.

You are not bad at this ... when you get it fixed, it'll be as good anyone's.

 

Quote:
Originally Posted by Lefuneste View Post

Following your discussion about repositioning, I've just found out about this great book on Dave's EEV blog. Everything you need to know about SMDs. It seems quite complete on every aspects you have to know!!

 

http://www.amazon.com/gp/product/1907920129/ref=oh_details_o00_s00_i00

 

Just ordered it from Amazon.com second hand. It's just been released and covers all techniques and concepts. You can get it with 4 SMD projects kit. It seems quite nice. Check out the review on Daves' blog. I think it's his January mailbag review. If you don't know this blog yet, then you are up for a night streaming...

 

That almost looks like a pupDAC PCB on the cover!biggrin.gif


Edited by tomb - 1/30/13 at 8:15pm
post #621 of 674

Honestly I found SMD soldering to be the easiest soldering I've ever done as long as you have a good iron, small tweezers, and steady hands. With the one-pad method Tomb mentioned there's no positioning to really be done, no leads to cut, no solder to juggle, nothing. Just solder a pad, flux it up to make the joint look pretty, heat up the solder, and slide the part into place. Helping hands are really nice to have, but not really necessary for SMD IMO.
 

post #622 of 674
Quote:
Originally Posted by Ikarios View Post

Honestly I found SMD soldering to be the easiest soldering I've ever done as long as you have a good iron, small tweezers, and steady hands. With the one-pad method Tomb mentioned there's no positioning to really be done, no leads to cut, no solder to juggle, nothing. Just solder a pad, flux it up to make the joint look pretty, heat up the solder, and slide the part into place. Helping hands are really nice to have, but not really necessary for SMD IMO.
 

This is the way I feel.  The PCM chips can still be a b*tch, but SMD resistors and capacitors are easier in the long run than through-hole.  I'd almost go so far as to say the SOIC opamps are easier than DIP-8 and plugging in the opamp.  At least with SOIC-8, you know you have a good connection and don't have to worry about bending the pins or having the contacts wear out.

post #623 of 674
Quote:
Originally Posted by tomb View Post

This is the way I feel.  The PCM chips can still be a b*tch, but SMD resistors and capacitors are easier in the long run than through-hole.  I'd almost go so far as to say the SOIC opamps are easier than DIP-8 and plugging in the opamp.  At least with SOIC-8, you know you have a good connection and don't have to worry about bending the pins or having the contacts wear out.

My only problem with SM resistors and caps is that they are easier to lose.  I have pushed too hard on them, while trying to hold them down to solder, and they go flying, and then tried to find them on a carpeted floor, or in a messy garage.  PITA.

I was better with the pupdac though, didn't lose any parts :)

 

 

Randy

post #624 of 674

yep, you get better by repetition and tweaking your approach. I used to try and hold parts down, but now I use the 'lots of rosin, tin a pad, rely of surface tension' technique. Some fine tweezers can then aid in fine adjustments to alignment before removing heat. Still - I always order a few extra smd caps or resistors. :-)

post #625 of 674

Just a bit of an update. I have a friend that is an electrical engineer, and he could not figure out what was wrong with it either, it just kept acting as if there was a short somewhere. He took it to work where he has all kinds of fancy equipment and lifted half of the PCM off of the board, to his surprise, everything was immediately fixed. I have a short inside of the PCM chip. I probably baked it a little too hot. In short, I feel a little better about my abilities (or lack there of!).

post #626 of 674
Quote:
Originally Posted by scootsit View Post

Just a bit of an update. I have a friend that is an electrical engineer, and he could not figure out what was wrong with it either, it just kept acting as if there was a short somewhere. He took it to work where he has all kinds of fancy equipment and lifted half of the PCM off of the board, to his surprise, everything was immediately fixed. I have a short inside of the PCM chip. I probably baked it a little too hot. In short, I feel a little better about my abilities (or lack there of!).

Well, it's good to know what the problem was.  Good luck on fixing it!

post #627 of 674
Quote:
Originally Posted by tomb View Post

Quote:
Originally Posted by scootsit View Post

Just a bit of an update. I have a friend that is an electrical engineer, and he could not figure out what was wrong with it either, it just kept acting as if there was a short somewhere. He took it to work where he has all kinds of fancy equipment and lifted half of the PCM off of the board, to his surprise, everything was immediately fixed. I have a short inside of the PCM chip. I probably baked it a little too hot. In short, I feel a little better about my abilities (or lack there of!).

Well, it's good to know what the problem was.  Good luck on fixing it!


Yep! I think that it happened while baking or trouble shooting, I may have shorted U2 and gotten 5V going to it, which would have been too much. I just ordered a few new chips, he's going to replace it for me, because he has way, way nicer tools. Evidently the pad going to U6 lifted on it, so we'll replace that trace with a bit of copper wire, it is really short anyway. Thanks for all the help. I'll report back when I get it fixed!

post #628 of 674

Would I run into any issues extending the USB lines to something like this mounted to a Hammond case?

 

I'm looking to put a PupDAC in the same case as a Pimeta V2 so I can save some space using only one enclosure and forego the RCA cables, but I've read that using wire to increase lead lengths on certain Amps/DACs is a bad idea..

post #629 of 674
Quote:
Originally Posted by Mikael109 View Post

Would I run into any issues extending the USB lines to something like this mounted to a Hammond case?

 

I'm looking to put a PupDAC in the same case as a Pimeta V2 so I can save some space using only one enclosure and forego the RCA cables, but I've read that using wire to increase lead lengths on certain Amps/DACs is a bad idea..

Can't predict everything, but you might want to slice up a USB pigtail cable or buy some USB shielded cable.  Depending on the proximity of the PIMETA, there might be some interference issues.  Shielded USB cable should do the trick.  The small exposed leads used to solder the cable into the pupDAC PCB shouldn't matter.

post #630 of 674

The proper way would be to use a short length of USB cable between the board and panel mounted socket. Don't forget to earth the shield, or it'll be useless.

 

I was gonna say you could probably use any shielded cable with 4 wires, but it may be problematic if the wrong wires are twisted together inside the cable.

 

Though when you consider that people created USB cables from nothing more than braided wires, you'll probably be fine using whatever you have on hand. If you have issues, then maybe try something better, but otherwise... Meh. Just give it a try and see.

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