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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    So, all of the Walnut X.3 PCBs have been fully populated, save for a couple of less than optimum mounting conditions for the amorphous core transformer option. Doug has worked with me for a fix and I'll have that in hand sometime next week. It has zero effect on operation; we are just always looking for the most robust way to assemble parts, especially when it comes to expensive transformers.

    The final PCB assembly also includes the power socket for the AC/AC walwart. The socket we chose is attached with a nut on the inside of the back plate. If it was hard-wired, that would make it impossible to remove the back plate without de-soldering. I need to emphasize that unlike the T4, which was designed to allow tube-rolling and changing jumpers for different wall power voltages, the Walnut X.3 is not really designed for disassembly. "No user-serviceable parts inside" as the ubiquitous warning labels state. ;) It's easy enough to remove the top plate, but the rest of the case assembly or disassembly can get quite complicated.

    Regardless, a de-soldering requirement for disassembly doesn't help anyone, so the power socket is attached to the PCB with Molex connectors. Here's a couple of pics, showing the procedure I went through to fabricate the power socket connections:
    [​IMG]
    Above, I have the gold Molex wiring pins, the sockets, and my trusty Ideal wire stripper. The wire is what I've used for over a decade for audio hookup wire: 22ga, multi-stranded silver-plated, teflon-coated from John's Wire Shop on ebay.

    After crimping on the Molex spring pins, I slide on a piece of heat-shrink on each wire lead, then sollder them to the power socket using my cheapo Harbor Freight helping hands:
    [​IMG]

    Once the power socket is wired up, I push the Molex spring pins into a two-pin housing for connection to the header on the PCB. Here's a power socket, with the Molex connector attached to the PCB:
    [​IMG]

    You may notice my makeshift binder-clip heat sink at front. More on that in the next post. ;)
     
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  2. TomB

    TomB MOT: Beezar

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    So, I'm fully in the testing mode of the PCBs right now. Of course, it's always gratifying to have a populated PCB - especially one this complicated (SMD, etc) - turn on and operate flawlessly the very first time it was wired up and plugged in. :D

    The first one, pictured as the last pic in the post above, was listened to for a few hours with my T4. As with all of Doug's ECP Audio designs, I quickly lose track of time as I get deeply involved listening to the music. The desire to hear one favorite clip after another becomes overwhelming.

    Suffice to say, the amorphous core Lundahls offer a level of detail I haven't heard before. Listening to Lana Del Rey, you can hear the movement of her tongue and lips in forming the words of the songs. When using the original HD800 (unmodded), with the detailed and slightly strident JJ 12AT7 tubes, it's a bit unsettling. I'm going to try a pair of the sweeter Mullard 4024 tubes today, but suffice to say, I LIKE IT.

    [​IMG]

    [​IMG]

    [​IMG]

    The binder-clip, makeshift heat sink is necessary for the U2 regulator. It's the only part on the Walnut X.3 that develops any consequential heat. The casework uses a solid-aluminum thermal bar, similar to the heat sink arrangement in the T4. It connects to the back of that regulator and is mounted to the back of the front plate, a solid 1/4" thick piece of aluminum. This provides plenty of "sinking" and in normal operation, you won't even feel the casework get warm. Heat rejection is still somewhat trivial compared to a tube amplifier such as the T4, but as noted above, we are always looking for the most robust method to design and implement part installations.

    I'll be proceeding with the casework this weekend and into next week, all the while thoroughly testing and listening to the rest of the populated PCBs. More to come ...
     
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  3. TomB

    TomB MOT: Beezar

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    Just a small update - although all of the DACs are assembled (except the transformers), I've run into an issue on one of them thus far. I was in the middle of tracing it down, but then my testing computer decided to crash. It's set up specifically for testing amps and DACs. Because of that, it doesn't always get regular use. Every time I turn it on, I have to go through a day or so of Windows and Norton updates. Unfortunately, once all the updates had been done, the Windows explorer decided to lock up every time I logged in - no menu, no taskbar icons, etc. I fiddled with it for a day or two, trying many things, but in the end, decided to clone a good SSD in another laptop.

    So after I got that re-built, the wireless mouse and keyboard decided to fail. It took me a few hours of switching about with other mice and keyboards and it turned out to be the USB receiver. It seems like one thing after another this week ... :(

    The fixes for the amorphous core Lundahls have been shipped as of yesterday. Hopefully, I'll get all of these problems solved and get back on track.
     
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  4. TomB

    TomB MOT: Beezar

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    Another update and I'll have some photos shortly -

    1. Doug got on the phone with me and after a little long-distance troubleshooting, we found out I had failed to solder an output pin on one of the THAT transistor arrays properly. Once located, I had it fixed in about 10 seconds and the DAC operates perfectly!

    It's one of the maddening things about SMD soldering sometimes: the joint can look perfectly fine, but the pin from the IC chip may actually be hovering directly above the soldered trace, but not actually connected to it. Measuring the continuity at the shoulder of the pin as it leaves the plastic IC body is the confirmation that it's not connected.

    2. It also took me awhile to come up with a dependable, robust method for the amorphous core mounting fixes, but I have that solved, assuming everything tests OK today.

    I apologize for the extra time this is taking, but it will hopefully all be worthwhile soon. :)
     
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  5. TomB

    TomB MOT: Beezar

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    So, to address item #2 above, and to let you know what's been taking so long, the following is an explanation for the amorphous core mounting. As it turns out, the Eagle library pin spacing that Doug used was about 1-2mm off in spacing from front to back. I can't assign fault to Doug, because I'm sure he's used these before. There may have been some changes in the pins that occurred after the time he used the library component. Whatever, the LL1684 amorphous core transformers would not fit in the PCB without carefully bending the pins inward to match the pads on the PCBs.

    I was fully prepared to make this adjustment. In fact, I completed one this way successfully (will become my own personal Walnut X.3). However, after discussing the issue with Doug, he convinced me from doing the others this way.

    Doug explained that the pins on the transformers are not really pins. My experience (except for the Lundahls on the T4) had been mostly with Edcor and Cinemag transformers that we used on the Torpedo series of amplifiers. With all of those, the transformer wiring is soldered to pins imbedded in the rails. So, the pins are truly "pins" as in other through-hole parts.

    With the Lundahls, however, the pins are actually tiny tubes. The transformer wiring is actually inserted into the tubes, then soldered as one assembly for each transformer winding lead and tube mount. This means they are not solid pins and bending them is trying to bend a solder joint with tiny - magnet wire inside. The chances of breaking those joints in bending is very high. IOW, I may have just been lucky on the one DAC I did that way. It may never survive the experience of shipping.

    So, Doug whipped up some adapater boards that I had made at OSHPark. Once they came in, I still had to figure out a method of assembly. Even though the pads adapted the pin spacing perfectly, it would still require fabricating and installing my own "pins" from spent leads and assembling the entire configuration while trying to keep everything aligned. This is much more difficult than it sounds, because when you try to solder the makeshift pins-from-leads to the Walnut PCB, the action also unmelts the pins from the adapter.

    I quickly realized that the pins were at the same location for both adapter and Walnut PCB on one end of the adapter. Thus, I only had to make the pins' correction on one end of the adapter.

    The first thing I needed was a jig, since I needed to this several times and ensure repeatability:
    [​IMG]
    Shown above is one of the transformer adapter PCBs. The 5 pins, with one staggered below a row of four, is the set of pins that I need to prepare. Unfortunately, the holes in that piece of scrap wood need to be accurately spaced by about 1/2mm or less. So, it took me a few times to drill the holes with that much precision. ;)

    I used spent leads that were as large as I had on hand - saved from some large film caps. I would insert them in the wood, place the adapter PCB over the pins, solder, then trim the ends flush:
    [​IMG]

    Once the five pins are soldered, I was able to remove the adapter board from the wood jig:
    [​IMG]

    Below, you can see a couple of the adapters finished, with another preparing to be soldered:
    [​IMG]

    One of the remaining problems is to ensure that the trimmed leads/pins, which will face the underside of the transformer, do not poke through the plastic film underbody of the transformer and possible short it out. I did this by applying two layers of 2 mil Kapton tape:
    [​IMG]
    NASA has used Kapton tape for decades. It is both heat-proof and electrically insulating and has been used in the harshest environments in outer space. Although as the actual assembly worked out, the act of creating solder joints itself prevents making actual flush fits with the transformer underbelly. Once soldered to the Walnut PCB, there's no up and down movement anyway. Nevertheless, the Kapton tape provides maximum insurance from shorting.

    Here the adapter board is show in its final position on the transformer. Note the five pin/tubes at left have been soldered to the adapter board and trimmed flush. The remaining four pins on the other side are actually long enough to solder through to the Walnut PCB itself. For added insurance and more robustness, I added the four extra pins and soldered them, too (not shown here):
    [​IMG]

    ... and here we have a completed Walnut X.3 PCB with the amorphous core Lundahls soldered in place with the adapters:
    [​IMG]

    Viewed from the side, you can see that the entire process results in a perfectly aligned, optimally spaced, and perfectly robust installation for the amorphous core Lundahls:
    [​IMG]

    Again, sorry this is taking so long. I'm still having contractor interruptions about every other day, now - instead of daily. So as that winds down, I'll be able to focus all my time on completing these soon.

    Soon that is, except for some trouble-shooting issues with the DACs, which I'll detail shortly. Some of you may be interested in trouble-shooting DACs, which I even thought was near impossible - NOT (as Doug Savitsky's assistance proves).
     
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  6. dsavitsk

    dsavitsk Friend

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    Nope, was 100% my fault :)
     
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  7. Grattle

    Grattle Friend

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    @TomB Thoroughly enjoying this thread. Thank you for sharing. Folks like you are what make this site such a treasure.
     
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  8. TomB

    TomB MOT: Beezar

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    I gave your post a "like," but it deserves a personal response, too:

    Thank you for your very kind statements. They are greatly appreciated. :)
     
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  9. TomB

    TomB MOT: Beezar

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    Good news! All of the Walnut X.3 DACs are performing! The bad news is that I had a bit of a struggle. The last two DACs, in particular, required some very involved troubleshooting. It all led to a good resolution, though.

    So why the issues? I believe I made a mistake in ordering the gold immersion pads. I vaguely remember having issues with red PCBs using gold immersion years ago, but I guess the memory faded enough that I though it was worth a try again. Literature suggests that gold immersion is best for SMD, primarily because it guarantees a consistently flat surface. That might work for a fully automated pick-and-place operation, but for me, it caused trouble.

    Plus, as mentioned before - the gold immersion allowing a flat/flush consistency was a moot point, anyway. The silk-screening is actually thick enough to interfere with tweezer positioning of the SMD parts anyway.

    The total lack of tinning anywhere is what I believed caused the issues. In one scenario, no pinning under the pins of the IC chips meant that it was easier than ever before to solder an IC chip and actually have a pin sitting above the pad, with no solder connection underneath. This can happen because rarely are the pins perfectly positioned out of the package. There are slight variations where a single pin may be a few hundredths of a milimeter above the rest of the pins. In manual SMD soldering, where the chip is held by tweezers and moved/positioned sideways, there is almost no top pressure applied to the chip. With regular tinning on the PCB pads, there's enough residual solder on the pads at the start to account for the anomalies of chips with pins that aren't perfectly flat.

    Two of the Walnuts had this issue, which was quickly fixed once troubleshooted and the offending pin located.

    In the other scenario, the lack of tinning with gold immersion resulted in a bridge forming underneath a couple of pins on the DAC chip itself. The last Walnut had this issue. Another Walnut - as mentioned before - simply had a bad SRC chip. Once replaced, the DAC worked right away.

    I mentioned that I used to think once power supply voltages were checked, there was not much way of troubleshooting a DAC. Doug taught me that's not true.

    Below is the general layout of the Walnut X.3 DAC PCB:
    [​IMG]

    If we take a close look at the area leading up to the DAC and out of it, we can focus in on this area:
    [​IMG]

    It'll be hard to see unless you blow the image up. It's 1600 x 1200, so you can see it clearly if you do that. The circuit goes like this:

    1. The Amanero USB board transmits the USB through the isolator chip. That's the multi-pin chip beneath the lip of the Amanero board, which sits up on top of that double-string multiple-pin connector array. To the right of the USB isolator chip is a white vertical ellipse labeled, "USB Stream."

    2. From the Amanero board and through that isolator chip, the USB stream is made up of four traces, encircled by that vertical ellipse. From there, the four traces lead to the SRC chip.

    3. The SRC chip turns the USB stream of those four traces into Asynchronous mode. This is one of the things that makes the USB on the Walnut superior. Asynchronous mode allows the DAC chip to take the USB stream at its own speed and controls the data speed. This reduces jitter significantly over other DAC connection methods.

    4. The four traces exit the SRC chip into a set of four resistors, where the traces continue on to connect to the DAC chip itself, the next IC chip above and slightly to the left of that row of four resistors. These traces can't be measured with anything but a scope.

    5. The actual fully differential output from the DAC are four vias, on either side of the DAC chip at the left, labeled, "Music Signals." From there on, the music signal is fully analog and can be measured with a DMM that's fully capable of measuring RMS of AC voltage.

    6. Power voltages are labeled around the DAC and SRC chips. Both chips require a 3 to 3.3VDC for digital power. The DAC chip also utilizes 5VDC for the analog music signal.

    In the case of the chip pins not flush and soldered underneath, it was actually the THAT transistor chip arrays shown here:
    [​IMG]

    The transistor array THAT (brand name) chips are circled for the Left and Right channels. You can also see the differential output traces circled that are leaving both chips and proceeding on to the transformer pads and RCA jacks.

    With a 100% signal, those differential traces should equal around 0.75VAC to ground, or 1.5VAC combined (or at the RCA jacks' pads).

    Doug helped me trace this route on the phone, long-distance, while I made measurements and relayed them to him on the phone. We found the issue in about 5 minutes. I quickly ran my soldering iron over the disconnected output pin on the offending THAT chip and measured the following to ground:
    [​IMG]
    0.771VAC on the Fluke 179.

    Measuring both differential legs, I got this:
    [​IMG]

    Problem solved! As stated, I actually did this to two of the DACs.
     
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  10. TomB

    TomB MOT: Beezar

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    The last two remaining Walnut DACs were a real puzzle. All the power voltages were correct, but I couldn't even get the 0.771VAC/1.54VAC at the DAC vias. So, was the DAC bad, the SRC chip, what?

    Doug suggested I use a scope. As it happens, my primary scope is a B&K analog unit (looks like a Techtronix clone) that Doug gifted me (nice guy!). However, I protested to Doug that the scope is only 20MHz. He said don't worry about it. I wouldn't be able to actually measure the wave, but it would give me a picture of what the proper waveform would look like on a good DAC and I could compare that with the problem DAC.

    I was a bit skeptical, but got my testing bench set up for the task:
    [​IMG]
    I have a PC laptop on a shelf behind that monitor. The monitor is on a swing mount, so I can move it around and out of the way as needed. The B&K analog scope is underneath. In the middle you see the DACs and my Fluke on the right.

    Just to complete the picture, here's my other bench - the building one:
    [​IMG]
    I made a lot of good use with that hot-air re-work station. ;)

    So, here was the plan: Use the PC to generate a 1K signal (Doug suggested 60 Hz, but I'm stubborn), connect the DAC and view the waveforms on those four traces.

    In quick succession, here's what each trace waveform should look like:
    [​IMG]
    (Scope on, no signal as yet.)

    [​IMG]
    Signal on, first trace measured - at the limit of the scope, but enough to see a very high frequency sine wave.

    [​IMG]
    Same waveform as above on the second PCB trace, but much wider amplitude.

    [​IMG]
    Third trace and we get some sort of square wave.

    [​IMG]
    Fourth and final trace - I don't know what it is, but it's distinct enough to remember and recognize.

    Bottom line, the non-working DAC had none of these images on the scope when measuring those USB stream traces. However, they were good at the isolator chip. Doug kept telling me the DAC chip was probably the least likely thing to be bad (because of his experiences in terribly abusing DAC chips ;)). So, I replaced the SRC chip with another one.

    Eureka! It worked. I got proper images on the scope, proper AC signal voltages on the Fluke and it sounded great hooked into an amp!

    Lastly, the last DAC was similarly affected. This time, I started testing even prior to installing the transformers. I narrowed it down to the SRC chip again, using the scope. Unfortunately, replacing the SRC chip did nothing to fix it. I racked my head checking everything else on the PCB, but somewhere between the SRC chip and the DAC chip, things were messed up.

    I finally remembered - the DAC chip "pulls" the USB stream from the SRC chip in Asynchronous mode, so the DAC chip could be at fault. I spied the DAC chip pins at great effort with a loupe I use and lo and behold - a bridge! Never saw it before, but once I cleaned it up, everything worked!

    On to casework!!!
     
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  11. Armaegis

    Armaegis Friend

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    Awesome progress pics notwithstanding, can we take a moment to appreciate how incredibly neat and tidy TomB's workspace is? Pegboard, shelving and drawers, power strip, monitor arm, he's even got natural lighting!



    Meanwhile in my basement soldering dungeon...
     
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  12. TheloniuSnoop

    TheloniuSnoop Almost "Made"

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    So noted, and envy button enabled.
     
  13. M3NTAL

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    @TheloniuSnoop - the DAC you brought to the meet was a X.1 or a X.3? I feel like it was the X.1 if I remember correct.

    For those that haven't been to any of the AZ meets - @TheloniuSnoop brings the true SBAF and early Head-Fi / Head-Case spirit with unique gear that always sounds awesome and has been tweaked by none-other than himself.

    I might actually need to bring the eXStata out to the next meet with the Audeze Carbon announcement. shocked face!

    @TomB - you rock! Thank you for taking time off forum to talk and give help.

    Cheers.
     
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  14. TomB

    TomB MOT: Beezar

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    Thank you for those kind remarks.

    About what I sent TheloniuSnoop - at the time, I was experimenting with some Ebay clones of the Amanero USB board. Not known to me back then (I thought they worked fine), they would randomly develop a "ticking" sound defect upon switching back and forth between high-res music selections.

    I didn't discover this until later when given a heads-up by a reviewer I'd sent it to.. The "ticking" was unpredictable, but a power-off-and-on could always reset it. What I didn't realize, though, was that the overall sound performance with the clone boards was not quite as good, either. That took ordering genuine Amanero USB boards and then comparing over time. I quickly stopped using the clone boards when I realized the problems. There may have been one or two that I sold that had the clone boards, but I'm positive I replaced the boards on all of them and never sold one without a genuine Amanero board again.

    (If you happen to have a Walnut, look through the cooling slots at the USB board. If it's green (not blue), it's a genuine Amanero. It's a weird juxtaposition of sound quality vs. build quality, but the genuine green Amanero board actually looks cheap and fragile, compared to the clone.)

    In addition - I've mentioned this before - the new amorphous core Lundahls are also at a different level of performance that the regular Lundahls. Hearing this is obvious when you are able to compare the two. The amorphous core Lundhals push the Walnut to a new level of detail and "plankton" harvesting, as Marv likes to put it.

    FYI - the only difference in Walnut X.1 and X.3, besides some connector location adjustments, is that X.3 has the pads for the amorphous core Lundahls (with adapters). The unit I sent to TheloniuSnoop was definitely X.1, with an Ebay clone USB board, to boot.

    All that's to say it's not surprising if the Walnut X was not terribly impressive at the time. Doug's stuff is inherently listenable over long periods, anyway. They don't usually impress during a noisy headphone meet where other equipment that emphasizes certain frequencies will stand out. The fact that the X.1 was saddled with a faulty USB board couldn't have helped.
     
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  15. TomB

    TomB MOT: Beezar

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    So ... I have three Walnut DACs almost ready to go. Casework is in progress.

    A fourth Walnut DAC is awaiting more Lundahl transformers. The Lundahl supplier is out of stock at the moment, but they've assured me that more are on the way, soon.

    Meanwhile, I cleaned and rinsed the three Walnuts with my standard method of 91% alcohol - rinse, dry, and repeat ... until clean:
    [​IMG]

    Here's the basic Walnuts, completed with the associated connectors, Amanero USB boards, etc.:
    [​IMG]

    You can see more adapter boards ready for the Lundahls at top. Unfortunately, those two cubes at top left are two amorphous core Lundahls that I ruined. They were on my personal copy of a Walnut, but had been soldered in by bending the pins into a force fit on the PCB. This was prior to my contacting Doug and making adapters. I tried removing them to use on the 4th Walnut that's been pre-sold, but destroyed them in the process. I should've left them alone, but didn't think the bent-pin-installation would survive shipping, anyway. It's an expensive mistake, but I learned a lot about Lundahl transformer pins in the process. :(

    Hopefully, Lundahl will have more in stock soon (they've indicated that was the case) and all will be well for the final Walnut and my own personal one.

    Good news is that the wood that Doug sent me is absolutely beautiful:
    [​IMG]

    Those are stacks of sides for the Walnut DACs - in Walnut, Bocote, Padauk, and Spotted Maple. For the time being, the Walnut will be used for the Walnut DACs. I might entertain use of one of the other woods by special request, though. ;)

    I'll be finish sanding them today, then will start applying the oil (hand-rubbed) on a daily basis. I'll try to get 4-5 coats on each one, but that means 4-5 days, too. It should be worth it. Some of the Walnut, in particular, has some iridescent graining that should look beautiful when finished.
     
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  16. dsavitsk

    dsavitsk Friend

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    Spalted maple :)
     
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  17. TomB

    TomB MOT: Beezar

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    OK - I couldn't read your sharpie marks on the tape holding the wood together.;)
     
  18. TomB

    TomB MOT: Beezar

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    The wood is taking a bit longer than I anticipated (as usual with me), but it should only be a few days, now, for the first three completed DACs. I've got at least 4 coats on them now (24 hrs between each coat), but they need a couple more, at least on the Walnut. Some of the other wood pieces were already finished, except on the edges. Most likely, Doug cut them down from existing pieces he no longer needed.

    Here are the pieces I've been working with:
    [​IMG]

    A few drops from that can, rubbed in on each piece, allowed to dry 24 hrs, then rubbed and another coat applied each time.

    The walnut pieces are completely unfinished. While they present a unique iridescence, it's because some of the grain is on-end and is taking a while to fill:
    [​IMG]

    Padauk:
    [​IMG]
    This one needs to be rubbed a bit more, which is why it appears to have a slightly dull appearance.

    Bocote:
    [​IMG]

    Spalted Maple:
    [​IMG]

    As stated before, the Walnut will be used unless someone has a special request. (I'll have to charge a bit more. The more exotic ones are not cheap.)
     
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  19. willsw

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    I am extremely impressed by this thread and the informative and remarkably calm way @TomB has documented all of this. This also felt like a weirdly accurate recreation of my typical work day (right down to still waiting on K&K to ship my transformers . . . ) except in a significantly more organized manner and heavily edited for exasperation. Very nice save with the Lundahl adapter boards, glad you didn't lose any transformers to that situation. Related to that LED polarity stuff, I think Lundahl has occasionally committed the datasheet sin of switching between "component side" and "top view" for different models' pinouts. Looking forward to the finished DACs.
     
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  20. TomB

    TomB MOT: Beezar

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    So, we're getting very close, now. It would be quicker if the wood finishing was behaving. I don't recall this much trouble before, but it could be the weather we've been having lately and humidity issues. Or, it could always be operator fault. ;) The problem is that the coats are taking 2-3 days to really cure, whereas overnight or 24 hrs should normally be sufficient. Regardless, I have at least 4-5 coats on all of them, so they should be done when this last coat cures. True rubbing oil takes time.

    Meanwhile, the casework is progressing steadily and quickly. Those of you familiar with the T4 thread will recognize the ECP Audio badge holders. These are small rectangles of clear, machined acrylic. They're machined in a plank of 10, so I have to cut them all out with the scroll saw:
    [​IMG]

    The painters tape is to keep the scratches off and also helps prevent the saw blade from grabbing into the plastic.

    After cutting them out, I glue them into the case top plates. Although, they're literally hammered into place beforehand. A rubber mallet, a protective block, and a couple of hammer blows to ensure that they're flush on the bottom. Then an application of CA gel on the sides and wait a couple of days to be fully cured:
    [​IMG]

    For some reason, the CA gel causes a gas to develop and leaves white stains on some of the plates. It's harmless and readily wipes off, but weird, nonetheless. I have to cut the plastic with bevels toward the front of the top plates, to leave clearance for the assembly brackets.

    Note also that one mounting hole for the top plate has been masked from the anodizing. As with the T4, this promotes good ground continuity throughout the casework.

    ECP Audio casework designs are quite complicated. I used to kid Doug that he designed puzzle boxes, not casework. The overall look is gorgeous, though, and worth the effort.

    Speaking of "effort," the amount of hardware needed to assemble ECP Audio casework is significant:
    [​IMG]
    That storage box is one of three just like it (one more is beneath in the photo). That's what is needed and runs the gamut from special screws, washers, brackets, standoffs, Loctite, heat transfer goo, etc.

    Here's the bottom plate added to the PCB as the first step in actual assembly:
    [​IMG]

    And with the bottom plates completely attached to the three Walnut DACs with transformers installed (still waiting on Lundahl for the other two):
    [​IMG]

    Speaking of Loctite, the front inside plate and back plate are assembled next. The screws get a dab of Loctite and are allowed to sit until dry - usually a day or two. This is for customer convenience, even though I've remarked before that the Walnut DAC casework is not really intended for customer disassembly.

    While the brackets form a very resilient and robust case assembly, disassembly results in the brackets swinging like a top on the screws. This makes it incredibly frustrating if one removes the case top, for instance, and then tries to line up 8 separate screws with 8 separate brackets that start spinning around. The Loctite adds some "grab" on the threads, preventing the brackets from spinning freely.
    [​IMG]

    Once the Loctite is dry, these will be attached to the bottom plates, already installed on the PCBs. Casework sides are next - complicated a bit by installation of the wood onto the metal sides. That'll be detailed next ... we're getting close to shipping these out, hopefully.

    EDIT: You can see another anodized-masked hole on the back plates.
     
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    Last edited: Aug 25, 2021

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