ECP Audio/Beezar Walnut X.3 DAC

Discussion in 'Digital: DACs, USB converters, decrapifiers' started by TomB, May 20, 2021.

  1. TomB

    TomB MOT: Beezar

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    PCBs arrived just a while ago!
    [​IMG]

    I chose the immersion gold because of its longevity and excellent flatness, important in SMD work. The difference is slight, but it yields the best finished PCB, I believe.
     
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  2. TomB

    TomB MOT: Beezar

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    The Mouser order arrived yesterday evening:
    [​IMG]

    Not very much volume for such a box, but the pin headers were in there, so they had to send it that way. DigiKey is still on its way, but I should be able to start soldering tomorrow morning:
    [​IMG]
     
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  3. TomB

    TomB MOT: Beezar

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    So the DigiKey order arrived:
    [​IMG]

    Interesting how DigiKey's environmentally-conscious packaging contrasts with Mouser's simple plastic bags.

    I also received more ECP Logo machined material from FPE:
    [​IMG]

    They like to include a small pack of Haribo gummy bears with their shipments. :p

    So, after receiving all of this stuff, I go through the really, really boring process of organizing it all. I try to fit all I can in that yellow-boxes case, while combining bags of the same parts and cross-referencing the BOM at the same time, to see if anything is missing. It gets confusing, because I forget things like not labeling the parts from DigiKey, so I have to look them up and figure out what I have.

    [​IMG]

    With that all done, soldering the PCB is next!!
     
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  4. Biodegraded

    Biodegraded Friend

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    Props for the multiple pairs of KSC75 on your tool wall :cool:
     
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  5. Azimuth

    Azimuth FKA rtaylor76, Friend

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    I always label the parts on the BOM. It makes it so much easier.
     
  6. TomB

    TomB MOT: Beezar

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    So, preparing for soldering SMD takes some organization, as you've seen. The second thing it takes is having the proper tools at hand. This is not really complicated, but again - just like checking the Bill Of Materials, I make certain that I have everything on hand before starting.

    There are a few parts on the Walnut DAC that are intimidating. If I've gone a length of time without soldering SMD, they make me very nervous. It's been over a year, so yeah, I'm a bit concerned. The Wolfson DAC chip and the SRC4190 chip are both SSOP-28 chips. That's just about as hard as it gets for anything you can do by hand. The other chip of slightly less concern is the ISO7240 chip, but it's an SOIC-16, which is very easy by comparison.

    So ... the tools are simple, but need to be of high-quality, to successfully solder SMD. First up is the soldering iron(station) itself. I've been using this Hakko 936 since 2007. Yes, the same one in this pic:
    [​IMG]

    Oops! It's more dusty than I realized, seeing it in this pic. Oh well, not bad for a tool that's been used quite a bit and is almost 15 years old. it's never skipped a bit. Sometimes, I wish it would to give me an excuse to buy the new blue and yellow one! Unfortunately, there's this at the top of one of my shelves:
    [​IMG]

    That's not an empty box. It's a brand-new Hakko 936 that I bought on special at Frys for $99, about a year after I bought the first one. I thought it might be good to have a backup. Unfortunately, Hakko made these things too damn good. I'm not sure I've even opened that box. :(

    Oh well - next up are tips. The Hakko, like a lot of high-quality solder gear, uses interchangeable tips. That lets you customize the same iron for different tasks. So, about the same time I bought the first Hakko, I bought all of these:
    [​IMG]

    ... including an extra sponge over there that I've never used - nor the one on the existing Hakko itself. I discovered the brass wool at about the same time and never use the sponge. Anyway, as usual, I way over-bought.

    These are the only two tips I've ever used with the Hakko:
    [​IMG]

    That's a 1.2D chisel tip that I use for all through-hole soldering and a 0.8D chisel tip that I use for all SMD. BTW, in the previous pic, there's a couple of Plantronics tips I ordered from Mouser once. I hate 'em. Don't use 'em. There's nothing better than the genuine Hakko. I've never used up the 0.8D, but did wear out the 1.2D tip, hence the Mouser Plantronics. I went back to another Hakko 1.2D tip as soon as possible and am still using it. Again, unbelievable quality exists in the Hakko stuff.

    So changing the tips is a simple procedure: unscrew the barrel nut, slide the tip and its liner off of the ceramic heating bar, slip the new tip and liner back on the ceramic, replace the barrel, nut and tighten:
    [​IMG]

    Next up is the solder:
    [​IMG]

    On the left is what I use for through-hole: Kester 63-37 eutectic, rosin core, at 0.025" diameter. The spool (those are 1lb.) is getting a bit low. That's the second one I've had since 2007. The one on the right is Kester 63-37, eutectic, rosin core, at 0.015" diameter.

    I once read (or watched) in Tangent's tutorials on SMD (highly recommended) that 0.015" diameter solder was really too small and it broke a lot. I haven't had that problem and it really makes a difference with tiny parts. It's a waste for through-hole, though. I know having both of these is tough to afford when you start out, but it really made a difference for me.

    Finally, the last of the important tools specifically for SMD soldering: tweezers!
    [​IMG]

    The top two at right are some "Golden Tool" tweezers I got at Frys. They got me going until several years ago, I purchased the black Wiha tweezers. I've actually never used that green one. I bought the curved tweezers because I thought I would prefer one of those in positioning the SMD chips, even though it seems everyone else uses the straight tweezers. I was right about myself, though, and the curved ones are all I ever use. The curved black Wiha tweezers are really great and I use that one almost exclusively.

    One other very important tool to mention is the flux pen. I couldn't do SMD soldering without all of the items mentioned in this post, including the flux pen. Again, it's a Kester product and that one tube at top has lasted me since about 2008-9. Turns out, it's finally empty, so I get to use the new one, finally.

    Anyway, the flux pen accurately dispenses a very liquid solder flux around the pads on a PCB. Not only does it suck up solder like a sponge, but it helps in positioning delicate chips. Use of this flux and applying a minimal amount of solder, is the real secret in SMD soldering. The metal pads and chip pins, combined with the flux, suck up the solder and prevent the solder from getting where it's not supposed to be.

    I've actually completed soldering the primary chips I mentioned on 5 PCBs today, but I'll post about it tomorrow. This is enough for today. ;)
     
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    Last edited: May 30, 2021
  7. TomB

    TomB MOT: Beezar

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    My problem is that I have the parts carefully labeled in the shopping cart on Mouser, but then when they don't have something, I get concerned trying to find it at DigiKey, Newark or Allied, and by the time I've checked prices of all three and added it to a shopping cart, I forget to label the part in the cart at DigiKey (or whichever alternate I used).

    Everything I got from Mouser was carefully and exactly labeled. ;)
     
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  8. TomB

    TomB MOT: Beezar

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    There are a lot more KSC75s than that laying around this room! I bought about 20 at one time several years ago, when Radio Shack was cleaning out their stock. Plus, I bought several at Amazon, and even two pairs of the black ones from MassDrop. ;)

    EDIT: I gave away many of the Radio Shack ones to friends and family over the years. I only have one unopened package left of them. Radio Shack put this stupid, very clunky in-line volume control in their versions (they were still made by Koss, though). That's how you can tell the difference.
     
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    Last edited: May 30, 2021
  9. Azimuth

    Azimuth FKA rtaylor76, Friend

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    I would love to see a video tutorial of this process. It might get me over my fear of SMD soldering. I have done a couple of SMD to SOIC op amp adapters and a SMD resistor or two for repair, but soldering by hand with my Hakko iron seems scary I would just make a blob of things.
     
  10. TomB

    TomB MOT: Beezar

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    SMD Soldering Described
    Tangent's Tutorials are how I first learned:
    Tangent Tutorials (tangentsoft.com)

    Specifically, his :TT #03: Surface Mount Soldering Techniques " is the one to watch, but they're all pretty good.

    In his video on Surface Mount, you'll see that his solder is too big (IMHO) and I use a chisel tip soldering iron instead of the pointed one he uses. I generally agree with his strategy - small components first, and components in the center of the board, first. However, after years of doing this, the economics are most important. That means the IC chips (DACs, Opamps, and Regulators, etc.) come first. Usually, the DAC chips are hardest. If you can't get that right, the rest of the PCB is a failure anyway.

    That said, you'll see that I modify that somewhat by "practicing" on a couple of easier chips, first - if it's been awhile since soldering SMD. He also doesn't mention the use of a flux pen. Those are magical, IMHO.

    To be honest, with complicated chips, I CHEAT. Everyone tells you never to apply solder to the iron, then the part. You are supposed to heat up the entire joint, then apply solder by letting the heat of the joint melt the solder. For SMD SSOP-28 chips? BS!!

    On DAC chips as you'll see below, I anchor the chip first. That's soldering - separately - each opposite corner pin. Once the chip can't move, I apply the flux pen liberally to the entire side of pins and pads. Then I apply a very small amount of solder to the iron, and touch it to the outer edge of the pins and the pads, moving down the entire row. The flux makes the pads and pins suck up the solder. When I get to a pin and the solder is starting to disappear, I remove the iron and apply a tiny bit more solder, then continue moving it down the row of pins until finished with that side of the chip.

    I go back repeatedly and reflow the soldered pins and pads with a horizontal sweeping motion of the tip held parallel to the board, sort of a rolling pin on dough, pushed to the outside of the pins, if you can visualize. This is explained as the "drag and wipe" method on my web pages for the various DACs I sell in kits. Here's the one for the PupDAC:
    pupDAC SMD Soldering (diyforums.org).

    This is only for the SSOP-28 chips and the like. For SOIC opamps, you should be able to simply solder one pin at a time. Use of the "drag and wipe" technique to reflow after initial soldering is always helpful, though. I do it a few times after initially soldering the chip, until all the solder and pins are shiny with no bridges. If you have a bridge, be certain to remove the iron, clean it thoroughly in the brass wool to remove any hint of solder, then repeat the drag and wipe reflow technique. The bridges will disappear. Of course, this all depends on not adding too much solder to begin with. Use of the small 0.015" diameter solder and a tiny tip soldering iron helps to ensure you don't apply too much in the first place.

    Finally, the SMD resistors and capacitors should be soldered exactly as Tangent shows. Do not use a drag and wipe or reflow technique after soldering SMD capacitors and resistors. You'll just push the component right off the pads and create a huge mess. When you do it with DAC chips and opamps, the chip is completely anchored by the pins on the other side. With small SMD resistors and capacitors, the heat of the iron is enough to melt the solder on the other side and the drag and wipe reflow won't work.

    Hope this helps ...
     
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  11. TomB

    TomB MOT: Beezar

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    So, referring to the above SMD Soldering Described, I proceeded to solder the primary chips to the PCBs. As mentioned, I was a bit intimidated after not having soldered any SMD for over a year. So, instead of the DAC chip, I began with the ISO7240 chip, instead. The ISO chip isolates the USB stream ahead of the DAC. This isolates the ground and other currents arriving at the USB board. It also includes digital buffers, which enable the SRC4190 chip to create the Asynchronous connection to the DAC. This means the DAC pulls the data from the stream at its own pace and under its own control.

    Anyway, the ISO7240 chip is SOIC-16, basically the same as an SOIC-8 opamp, except twice as big. It's a good chip to solder first and let me get accustomed to the techniques again. (It's not exactly like riding a bike.)

    Here's where I did the first step: apply flux with the flux pen and apply solder to one of the corner pads:
    [​IMG]

    And a closeup that lets you see things better:
    [​IMG]

    So, the next step is to grab the ISO chip with tweezers using my left hand (ensuring proper orientation!!) and re-melt the solder on the pad with the soldering iron in my right hand. After moving the chip into position, while holding the soldering iron to keep the solder melted on the pad, I make sure the pins are all lined up on the pads, then remove the soldering iron - still holding the chip in place with the tweezers - and wait a couple of seconds for the solder to cool.

    * Note: the "ET" stamp above the arrowhead is Imagineering's reference that they electrically tested the PCB prior to shipment.

    Next, the opposite corner pin is soldered and it locks the chip in place:
    [​IMG]

    Keen observers will note that I am indeed out of practice and offset the pins on the pads by a bit. Not to worry - it's not enough to affect operation. Some of it is also a bit of an optical illusion, due to the angle of the camera.

    Once that was accomplished, I finished soldering all the pins and gave each row a "drag and wipe" reflow as mentioned in the post above. Things went along steadily after that and all 5 PCBs have their ISO chips soldered in this pic:
    [​IMG]

    Next up is the SRC4190 chip, then finally, the DAC. Here's all 5 PCBs with those chips soldered:
    [​IMG]

    And a closeup of one of the PCBs:
    [​IMG]

    If you look closely at that pic, I got progressively better as I went along. The SRC Asynch chip is a bit messy, but the DAC pins look very clean and proportional. The slight mess on the SRC chip may just be flux, though. It's very hard to tell at this point - more on that in a moment.

    The next step is to solder the other chips - the AD825 chips (2 each) and the THAT transistors arrays (2 each). When that's complete, I'll actually clean the PCBs with repeated alcohol rinses until all the flux is removed. Then a re-check of all the pins will be done. Any suspect joints will again be re-flowed before proceeding with the rest of the soldering work. Again, if these chips are not correct, it becomes very difficult to fix them once they're surrounded by dozens of other parts.
     
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  12. TomB

    TomB MOT: Beezar

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    The AD825 opamps (used in the power supply for the DSHA output buffer) and THAT transistor arrays (the DSHA output buffer) are now soldered:
    [​IMG]

    And on all 5 PCBs:
    [​IMG]
    Yes, I have to use some de-soldering braid as I go along, mainly to clean up adjacent pads that get hit with solder when I do the drag and wipe on the chips' pins.

    Last pic of the day - a closeup on one of the PCBs of the DAC chip:
    [​IMG]

    So, is that flux or bad soldering? I've seen it with my naked eyes, so I know it's 99.9% good soldering, but the flux pen flux adds one helluva lot of glare. This is exactly why I'll spend the next step alcohol rinsing the PCBs until the flux is removed and checking one last time.

    One thing of note: I have to re-evaluate the reputation of the gold-immersion pads, at least with Imagineering. The silkscreen is of outstanding quality. Unfortunately, that means it's thick. It's so thick, in fact, that it's upsetting the chips as I try to position them on the pads. The fact that the gold immersion pads are ruler flat is wasted because of the interference of the silkscreen. The next ones will be regular silver/tin. ;)
     
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  13. Beefy

    Beefy Almost "Made"

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    I was wondering why there were AD825 in there in the previous post! Seemed a bit off-design for the signal path, but I do now recall I have seen that OPAMP is many different power supplies.
     
  14. Cspirou

    Cspirou They call me Sparky

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    yep. The power supply in various Gilmore amps use an opamp for feedback to make very low noise.
     
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  15. philipmorgan

    philipmorgan Member of the month

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    @TomB is a small size reflow oven (ex: https://smile.amazon.com/dp/B08CKDS2HV) an option for projects like this? My guess is a hobbyist who is going to solder a few SMD components/year just needs to cowboy up and do it by hand, but the geek in me is curious whether a reflow oven is viable for something like your DAC project.
     
  16. dsavitsk

    dsavitsk Friend

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    I have a reflow oven like that that I have used when doing large numbers of boards. I also have a hot plate which some people prefer, but which I never actually used. You can place solder with a stencil, or a pneumatic solder dispenser. The oven helps, but it's not a cure all. You still have to place all the parts. You also still often need to clean up between pins, and the solder can dry out before you get all the parts on if there are enough of them. I ultimately switched to just paying to have it professionally done. For a one-off, soldering SMD is really not that difficult. You just need good tweezers.
     
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  17. Cspirou

    Cspirou They call me Sparky

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    i hacked a cheap toaster oven with a temperature controller and I had the best soldered parts I've ever seen.
     
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  18. TomB

    TomB MOT: Beezar

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    If my attention to detail and quality, along with verbose explanations, imply that I'm struggling - I'm not.

    Doug pointed out the non-solution for reflow ovens. If we were doing 50 instead of 5 PCBs, it would make sense. Even then, though - as Doug alluded to - the thing that really saves the time is Pick-and-Place. I've had that done professionally in the past, too. In small volumes, it is not really on the right side of the cost margin, either. It depends on the complexity of the PCB, the number of parts, and the anticipated volume. When I used it in the past, it was only to install the difficult chips like the ones I've already done here.

    However, the purpose of using Pick-and-Place in the past was not for my benefit (at least not directly). The purpose was to ensure successful DIY builds for the PupDAC by removing the expensive, difficult-to-solder chips from the equation. Prior to my using Pick-and-Place, customers would buy the kit, be unable to successfully solder the difficult chips and then I'd feel obligated to somehow help them out with full or partial refunds. The same thing happened with the T3's CCS boards, which is why we stopped selling them as kits altogether, toward the end of the T3 run. ;)

    I've got to prepare and ship some "regular" Beezar Audio orders today, then because grass grows, I'll be spending the afternoon getting the yard in shape. So, you probably won't hear from me again until tomorrow sometime, when we'll continue with the rest of the SMD parts. :)
     
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  19. TomB

    TomB MOT: Beezar

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    Here are the rinsed PCBs with closeups on the SRC and DAC chip. The other chips are SOIC, so are trivial to spot issues with the naked eye. Boards 1 through 5 are shown. There's still some flux and drying towel lint on some of them, but it's sufficient to confirm no bridges and that good solder joints exist on all the pins:

    PCB #1
    [​IMG]

    PCB #2:
    [​IMG]

    PCB #3:
    [​IMG]

    PCB #4:
    [​IMG]

    PCB #5:
    [​IMG]

    These are hand-held shots from my smartphone, but good enough. :)

    Edit: Keen eyes will see that some of the solder trailed off into the traces or a few traces have been exposed. This is typical with the drag-and-wipe method, but has no effect on functionality.
     
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  20. TomB

    TomB MOT: Beezar

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    Progress continues steadily.

    The first image is of the last "IC" chip - the TI TPS3809 voltage reset chip. It's a SOT-23, 3-pin chip, so quite small with very tiny pins:
    [​IMG]

    After that, I started in with the SMD capacitors. There are two reasons for this: 1) there are a few 805-series parts on the PCB (all the rest are 1206), and 2) capacitors are often the closest parts to the DAC and high-level IC chips, so they are usually located near the center of the PCB. Center-out is also one of the strategies used in hand-soldering PCBs with SMD parts.

    Here is one of the 5 PCBs with all of the SMD capacitors soldered. The other 4 have their SMD capacitors completed, also:
    [​IMG]

    Next up are the SMD diodes, then SMD resistors. Only through-hole parts will be left after that. So, completion of the PCBs by sometime next week seems fairly certain.

    EDIT: FYI - the 805 capacitors are in a row below the THAT transistor array chips at mid-left.
     
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