ECP Audio T4 Headphone Amplifier

Discussion in 'Headphone Amplifiers and Combo (DAC/Amp) Units' started by TomB, Aug 6, 2018.

  1. TomB

    TomB MOT: Beezar

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    All along the way, Doug kept suggesting the Audience Auricaps. I thought they were too expensive and that a hidden treasure could be found in cheaper caps such as the CDEs. Of course, I'm not a cut-and-dry objectivist, but I still have a developed prejudice against voodoo capacitors.

    He convinced me try a set, though, and while were investigating other potential tweaks in the prototype, I purchased and received a couple of the Auricaps. Wow! Full body, more detail, superlative dynamics, etc. I was sold and claimed the Auricap XOs as standard from then on. Auricaps were not voodoo!

    After messing around with the CDEs and then installing the Auricaps, I noticed that there were definitely differences in volume output, depending on the capacitor matching. It's not as much as with mis-matched tubes, but it was still audible. So, I began with matching the capacitors in using Auricap XOs installed in the T4:
    [​IMG]
    These caps are all spec'd at 4.7uf, so you can readily see the difference in the Fluke 179.

    For this set of six T4s, I had ordered 20 Auricap XOs. Here they all are with measurements labeled on the bottom of the caps:
    [​IMG]
    As you can see, they vary from a low of 4.79uf to a high of 4.86uf. Matched pairs were selected and I proceeded with installing them in the PCBs.

    The Auricaps are different than most film caps in two ways:
    1. They specify a shield and which direction it should face in the circuit (faux polarity).
    2. They use double leads on each end!
    They solder the double leads themselves from the factory, but leads on caps are always longer than needed. They are also longer than the minimum that causes trouble, so cutting them was no choice. It always scares me though, because you cut too much and you're up the creek. I had long ago documented the proper length for the T4, however (with a generous safety factor).

    Here's a pair ready to be installed with the leads cut to proper length:
    [​IMG]

    With caps this big and flexible leads (even if not), it takes more than just soldering them into place to keep them secure. To the right in the pic above, you can see four pieces of double-sided ultra-high-bond 3M tape. This stuff is clear, 2mm thick, and used in bonding materials in the aviation industry. So, it's not trivial tape. ;)

    I use two pieces of tape per cap, placed lengthwise on opposite sides of the capacitor centerline on the PCB. After soldering them in place, I press down firmly on the cap, where the curvature touches the bare PCB right on the centerline, but is making contact with the tape on both sides of the centerline as in a saddle, so to speak.

    This shot shows the tape in place at both capacitor positions, with the secondary film still in place on top of the tape:
    [​IMG]

    And with the caps installed (double leads in separate pads and soldered separately):
    [​IMG]

    The above is actually an improvement over this version of PCBs. After the first T4s were sold, I contacted Doug to order more. He asked if there were any changes that were needed. I told him we needed four pads for each parafeed capacitor, because of the Auricap double leads. In previous builds, I wrapped the stripped portion of one lead around the stripped portion of the other lead, leaving a knot of soldered lead above the PCB pads. Although functionally equivalent, it was an added hassle for me in building. This was a more straightforward improvement.

    Not so simple for a capacitor install, huh? At least it is light-years simpler than those four Mundorfs in the T3.;)

    One other improvement was made in this batch of PCBs - an extra mounting/standoff hole near the power rectifiers. You'll see that in detail with posts about the casework assembly.
     
    Last edited: Apr 26, 2020
  2. TomB

    TomB MOT: Beezar

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    The choke more or less completes the population of the PCB. There's still an LED to add, but it stands proud and vertical to light the ECP Audio logo in the case top. So, I leave it last to protect from bending or knocking it off. Once the amp is assembled, it's well-protected by the casework.

    The chokes are made in Canada by Hammond Mfg. This is how they come from Mouser and elsewhere:
    [​IMG]

    Opening the box:
    [​IMG]

    The choke is a greater hassle in installation than it should be. Like the IEC inlet, it's a combination of mechanical and electrical installation. That's all steel there, so the choke is bolted to the PCB by the two tabs on the sides. Then there are two leads that are soldered into the PCB.

    Unfortunately, that traditional bent-steel channel frame is very poor at dimensional control. The mounting tabs are rarely straight and parallel to the horizontal. The tolerance in the distance between those mounting holes is also very large. Finally, the lacquer used to seal the core (just like a transformer) appears to be applied after everything is assembled. There's lacquer on the wire leads that breaks off when you flex them and there's often lacquer covering the mounting holes and collected in the bend at the mounting tabs. You have to clean all of that out, or the mounting screws don't fit, won't go in at a vertical angle. Worse yet - if not cleaned, the lacquer can deteriorate over time or break off during shipping. That results in the screws coming loose and potentially having the choke come loose from the PCB!

    When shipping the T4 prototype loaner from place to place, I once got it back after two or three shipping trips and found the choke held on by one screw and the remaining hardware rattling around inside the case! So, great care should be taken in removing the lacquer around the mounting holes, etc.

    The tabs themselves, in addition to not being horizontal, are actually higher than the bottom of the choke. I've developed a practice of placing two washers between the tabs and the PCB so that everything is as orthogonal as I can get it.

    Here is the choke installed:
    [​IMG]

    PCB finished and complete:
    [​IMG]

    And, once again - all 6 PCBs populated:
    [​IMG]

    Power transformers are next!
     
  3. Baten

    Baten Friend

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    You are slowly convincing anyone on the ball for buying this amp ;) loving these progress updates
     
  4. MichaeLeroy

    MichaeLeroy Almost "Made"

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    +1 to @Baten as well to all of the great posts by @TomB

    I've been following this thread closely. In part because one of the 6 units has my name on it. But more importantly because it is great to learn just how much thought, care and experience goes int the production of these amplifiers. The engineering that goes into these is impressive (details sweated, challenging tradeoffs made). I had thought that I was making an extragavant purchase of an expensive amp, but after learning how much care and effort goes into these, they are clearly a bargain.

    I apologise in advance if this is a Rando noise post. I've been holding off comments for a long while, feeling shy about being intrusive before I had any sonic observations to add. I do plan to spend some qualty time with the amp once I get it and to contribute my observations. I'll be quiet until then unless invited to contribute.
     
    Last edited: Apr 28, 2020
  5. StageOne

    StageOne Friend

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    As a owner of a T4, this has been highly educational and it's amazing the care and thought that goes into these amps. Thanks @TomB

    I noticed 2 of the 6 amps have a red, cubical component and the other 4 are blue. Sorry I'm not sure what that actually is, but are they for different purposes or same part, different builds?
     
  6. File1man

    File1man New

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    I'm on pg 3 of your 2018 t4 beezer amp story.im looking to buying my first tube headphone amp. Cans are my focal elear, drop 6xx(senns hd650), m1060. Ohm 80, 300,50; sensitivity DB 104,103,96. Never had tubes, so cant fix them, tube rolling not likely. My ears are way overly sensitive, so my jutenheim is piercing & harsh. Preferred a $1k budget. Did you buy a beezer t4. Been away from here, headfi , etc. Was saving for a don sachs tube amp but it went from 2017 $2300 to 2020 $3600.suggestions. I read about the tor $960 balanced, non hybrid with only 1 review and a tuga $650. What did you spend your funds on
     
  7. Ice-man

    Ice-man Friend

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    Although I enjoyed the t4 very much, I ended up buying a headamp gs-x mini. Mainly because I needed to drive planars as well as dynamic driver headphones and I didn't have money for two amps. If I'd ended up with hd650 and hd800 the t4 would have certainly been my amp.
     
  8. TomB

    TomB MOT: Beezar

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    Good eye!

    The giant film cap in the center of the PCB is the traditional film cap after electrolytic in the high-voltage tube power supply (B+). The blue ones are Epcos, a very fine quality film cap. However, the red ones are Wima MKP10, among the finest box film caps available and if I'm not mistaken, even more expensive than the Epcos. I had a couple on hand and thought I'd try them in those positions. They were used (as were the Epcos) as parafeed capacitors on the prototype T3s. (Not these actual caps, though!) If there is any deleterious effect when I audition all six T4s, I'll replace them.

    There is almost no chance that would happen, though. Any good quality film cap should work well in that position (power application). The Wima MKP10 is one of the best box film cap series in the world. I don't think this really matters, however, because it's not in the signal path. Humble Homemade HiFi actually ranks the Wima MKP10 higher (8) than the Epcos (7.25). Again, however, that is for audio quality and says nothing about power quality.

    I suspect it's sort of like comparing a Nichicon UPW electrolytic capacitor with a Panasonic FC, or a Nichicon UHE with a Panasonic FM. You'll drive yourself crazy trying to figure out which one is better in a power application.
     
    Last edited: Apr 29, 2020
  9. TomB

    TomB MOT: Beezar

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    I gave an answer to this from your post on another forum. It's only one answer, though. Some may agree, some may disagree. Ultimately, it's my own opinion and I'm obviously prejudiced. ;)
     
  10. TomB

    TomB MOT: Beezar

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    While I start work on the power transformers, I also start rinsing/cleaning the PCBs. I'm not sure anyone does this anymore, but I've been told that stray flux will corrode over time - or at least collect loads of dirt and stain - and eventually get so bad that it will conduct electrical current. So, I was always taught to clean up a soldering job.

    Many people recommend flux - the more, the better. Generally, that is true, especially if you are soldering metal-to-metal for strength joints. I go way back (an old fart, now) and first started soldering to build brass slot car chassis in the late 60's. I was still only a teenager. Back then, the order of the day was Kester rosin-core solder, with a hockey-puck sized tub of Kester soldering paste. Soldering irons for brass were best with an Ungar. You'd dip the end of the solder into the tub of flux, wait for the iron to melt/boil the flux paste on the end of the solder, then apply the solder. it worked well and was even fairly easy to clean up on the brass chassis that was built.

    Electronics soldering is different. The parts are small and delicate. Too much flux and it becomes a nightmare to clean, and damaging parts becomes more likely. So, I like to use flux only when something gives me trouble soldering - or with SMD. I always use a flux pen with SMD. The flux quickly partially dries into almost a glue. So, it helps to stabilize the part while soldering. In a lot of cases, a full flush of alcohol works quite well, so cleanup is not so bad - even with the additional flux - in using SMD. Without leads, the parts are not so delicate. There are always exceptions, of course.

    The solder I use is still Kester rosin-core, but is eutectic 63-37. The rosin core, 99 times out of 100, is sufficient flux to make a great joint. It still leaves quite a bit of flux residue, however.

    So … I rinse and clean every PCB with alcohol. I do this until most, if not all, of the flux is removed and the PCB is nice and shiny. It's not rocket science and very rudimentary, but I wouldn't feel right selling an electronic product without doing it. The pic below shows the basic tools (very complicated! ;)):
    [​IMG]
    Walmart 91% isopropyl alcohol, a used butter tub, old toothbrush, and paper towels. (The Pug soap dispenser is optional.). I also use Q-tips, but more on that later on.

    On the other side of the sink, the PCB is placed top down on a set of paper towels:
    [​IMG]

    Looking at the pic below, you can see why this is necessary. The area around the tube sockets are worst, because of all the solder I use to make a good mechanical joint:
    [​IMG]
    Notice the large clear bubbles of solder flux residue around the tube socket pins and all the other leads, too. This is what we want to remove, so it won't cause issues years later. If you've ever opened up vintage electronic equipment, you'll know what I mean. Even stuff made in the 80's and 90's can look pretty rough if the flux was not cleaned off.

    It generally takes about six rinses of alcohol, applied with the toothbrush by dipping into the butter tub, coating the PCB with the brush, and rubbing/brushing at the leads and pins where the flux collects. Then I pat up the dissolved alcohol/flux with paper towels, before the alcohol completely evaporates. As said, it's far from rocket science and very tedious, but necessary.

    I use the simple Walmart 91% alcohol because it works best. I purchased some commercial flux remover solution years ago, but just using a little almost knocked me out. It also didn't remove the flux as well as simple alcohol. I've never used it since. Sometimes the alcohol fumes get strong, but TELs are quite high for alcohol and the coating is quite thin. I think it works the best.

    Here's what it looks like after the first rinse. One might think it's not worth the trouble, because this looks ten times worse than before we started, with streaks and gunk everywhere:
    [​IMG]

    This shows the paper towels absorbing the dissolved flux/alcohol rinse. When it's thick, the paper towels will turn a yellow-brown where it picks up the mixture:
    [​IMG]

    Believe it or not, this pic is very, very close to being completely clean. When it looks like this - dissolved white powder everywhere - it means that the hard, dried flux bubbles have all been dissolved and are drying as a fine rosin powder all over the PCB. From this point, it only takes about two more rinses:
    [​IMG]

    Here is a PCB completely rinsed, nice and shiny:
    [​IMG]
    The Q-tips at bottom are used for the top of the PCB, to clean off the flux-pen residue from the SMD transistors.

    Here's a closeup of the tube socket area that we pictured above - big difference, now!
    [​IMG]
    Note that the slight bulging around the tube socket pins is NOT flux, but the FRP of the PCB material, bulging at the edges of the holes because they are so large for the tube sockets. It is not flux.

    And the rinsed top of the PCB:
    [​IMG]
    The Q-tips make it easy with the flux-pen residue: one tip to apply the alcohol, the other tip to wipe it up. It's a bit harder than that sometimes, but not too much.

    Thanks for your patience! I know this is not flashy stuff, but a necessary part of the building process.
     
    Last edited: Apr 30, 2020
  11. Failed Engineer

    Failed Engineer Friend

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    @TomB This is phenomenal stuff. I'd love to see a play by play of the DAC build someday.
     
  12. atomicbob

    atomicbob dScope Yoda

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    I think your T4 assembly progress series serves to demonstrate why the T4 is more than just Bill Of Materials (BOM) cost. Two parts that many may not appreciate are the design efforts along with the assembly exercise. As can be seen there is a lot of labor involved. Each amp is special having been created from a passion for good sound. These are small production run components, not 1000 unit automated factory production builds.

    I wish to repeat that Tom doesn't just assemble and run a few measurements, he also listens to each amp before they are shipped as a final QA step.
     
  13. TheloniuSnoop

    TheloniuSnoop Friend

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    Ah, slot cars. I remember them well. In our small town, when the track there first opened around 1966, the kids couldn't get close to it in the evenings because the adult motor heads were hogging it.

    I've enjoyed your build log posts here, Tom. Picked up a couple of tips too. Thanks for all your efforts.
     
  14. gepardcv

    gepardcv Almost "Made"

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    This is so cool! I use 99% alcohol from Amazon to clean circuit boards, good to know the more commonly-available pharmacy stuff works, too. Also good to know I'm not crazy for doing multiple rinses, I thought I was doing something wrong when the first one always left PCBs sticky and gross.
     
  15. File1man

    File1man New

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  16. TomB

    TomB MOT: Beezar

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    While I'm still rinsing the PCBs of flux residue, I've also begun work on the power transformer. These are the very last steps prior to final assembly with the casework.

    The power transformer connections and mains voltage setting all use the Molex KK254 terminal system. These are convenient crimp-on terminals with a dizzying array of housing and header offerings. Dsavitsk and I originally thought that we would be able to order the transformers with the headers already installed. Unfortunately, that did not turn out to be the case. So, the original prototype and loaner T4 were built with the power transformer leads soldered into place and the voltage setting jumpers were spent leads soldered into the PCB pads.

    There were two issues with this:
    1. Soldered mains voltage setting jumpers do not allow for user-changed voltage settings.
    2. Because the transformer is mounted to the case bottom, disassembly becomes very difficult if the leads are soldered to the PCB.
    With #1, this is a missed opportunity for convenience, because the power transformers are spec'd for 220V-110V windings and the IEC inlet allows the use of all types of domestic and international cords/plugs. However, if the actual voltage setting on the PCB requires soldering skills, this severely limits the options to the customer. So, if a US customer eventually wants to sell his/her amp to an international customer, soldering skills are necessary - even more, sufficient soldering skills to remove existing solder and jumpers.

    With #2, there are a total of 9 leads from the power transformer that attach to the PCB. When assembling or disassembling, the fact that all the leads are soldered to the PCB, yet the transformer is bolted to the case bottom, means that assembly/disassembly is awkward at best, potentially damaging to the transformer at most.

    So, once I started building T4s for sale (after the two prototypes), I started researching the Molex KK terminal system. Unfortunately, as noted above, I've never encountered any other parts system that is as widespread and confusing as the Molex. I eventually settled on the KK 254 terminal system, which seemed to be the proper choice for 22 gauge wiring and a 2.54mm pitch (pin spacing on PCB). I used the headers with friction locks, housings with both locking ramps and rib "wings." All pins and crimp terminals are gold.

    The next step was to acquire a crimper tool. Knowing that this would be used for hundreds of crimp processes, I wanted to get the best tool available. So, I started looking for the actual Molex-brand tool: about $350, everywhere I looked. Well, that ended that. So, I started searching elsewhere and finally settled on this IWISS tool from Amazon:
    [​IMG]

    It's Chinese and those handles are basically completely styrene, not mixed plastic with a gray rubber grip. However, the crimping die seemed of good quality and it got pretty good reviews, so I gave it a shot. It seems to be working OK, although you have to hold it upside down to use it properly. I have thought about removing the dies and re-installing them reversed, but I haven't had the time to try that, yet.

    Here's a pic of other tools I used for the Molex terminal system:
    [​IMG]
    Besides the IWISS tool, there's a set of Ideal Stripmaster wire strippers, a Lowes wire cutter/stripper, and a Harbor Freight 98-cent smooth-jaw needle nose pliers. Not pictured is also an X-acto knife that I use for the crimp terminals - more on that later.

    Here's a pic of all of the Molex KK254 system pieces that I purchased, organized in a Harbor Freight parts box:
    [​IMG]

    And … here's a pic of the SumR toroid power transformer used for the T4:
    [​IMG]
    The transformer comes just as you see pictured, with two rubber mounting pads and a steel rubber clamp washer. No mounting bolt, nut, or washer/lock washer was included.

    For perspective, here's the entire arrangement laid out on one of my work tables:
    [​IMG]

    The first step I'm going to do is to make more Molex shorting jumpers that are used to change the voltage setting. Here's an excerpt from the T4 manual:
    [​IMG]
    [​IMG]

    So, these jumpers provide the mains voltage setting capability, as indicated. Two jumpers are supplied per T4, so any customer can switch back and forth between 110VAC to 220VA mains voltage.

    There's probably some Molex shorting jumpers already made and available somewhere, but none of my searching turned anything up. It may be that they're not manufactured for the KK 254 series, but are available for smaller series such as those used on PC computers that we've all seen. Anyway, it's good practice to do with the crimpers, strippers, etc., before starting on the very costly power transformers.

    For the ongoing six T4s under construction. I'll need 12 shorting jumpers made up and a couple of extras, just in case. We begin with the hookup wire. I've used John's Wire Shop (user: navships) on ebay for years. He sells great multi-stranded, Silver Plated Copper (SPC), Teflon-insulated wire. It comes in all different sorts of colors and he offers it in lengths that won't require a bank to purchase and a storage shed to store:
    [​IMG]
    Above is a recent set I purchased of five different colors, 10 feet each. Three are multi-color and then two are purple and brown, respectively. Again, very convenient for hookup wire. The Teflon insulation is also practically melt-proof and does not shrink away from a joint under soldering, like cheap PVC-insulated hookup wire. The only drawback is that his wire is probably not appropriate for headphone cabling, since it's so stiff. Stiff is good for hookup wire, though - it stays where you put it and at the same time, doesn't compress or smash very easily. All in all - good stuff!

    Also in that pic, you can see some of the shorting jumpers already made (3 of them) and then new, empty, two-pin housings (white things) and some gold crimp terminals at right above the brown wire.

    What I'm going to do is cut the wire, strip the wire, crimp the terminals on the wire, then insert them into the housings. That's up next!
     
    Last edited: May 5, 2020
  17. TomB

    TomB MOT: Beezar

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    Making the Molex shorting jumpers helps me transition from thinking totally about soldering to thinking totally about not soldering, but making mechanical connections. The shorting jumpers are small, simple, and help me get into a rhythm in using the crimper and the Molex terminals and housings. There's a lot of things to remember if you don't do this every day:
    1. How long to cut the wire
    2. How much insulation to strip off.
    3. How to place the crimp terminal in the crimper
    4. How to insert the crimped terminal into the housing
    It's better to re-learn all of that on a small, inexpensive shorting jumper - than hundreds of dollars of power transformers. ;)

    Pictured below is a KK 254 crimp terminal:
    [​IMG]
    There are two lugs and then the bent, looped portion is what makes the terminal electrical connection. The stripped portion of wire must be long enough to insert in the lugs from the left, so that the wire extends slightly beyond the 2nd lug. The idea is that the lug on the right crimps around the stripped portion of the wire, while the first, larger lug crimps around the wire insulation. The combination makes an electrical/mechanical connection with the small lug, then a second mechanical-only connection with the large lug. It makes for a very stable, secure connection. However, it's very important to get the correct length of the stripped end. Looking at the ruler, this works out to about 1/8" (the ruler is showing 32nds on top).

    I won't go into detail about the IWISS tool. If you are interested, you can refer to this review on Amazon that is actually a tutorial on using the tool. (One of the major complaints in the reviews is that the tool doesn't come with a manual.) Here's the link: How to Use the IWISS Ratcheting Crimping Tool. Suffice to say that placing the crimp terminal within the dies of the crimping tool, and inserting the wire, is critical. Thanks to the tool, though, the act of crimping is not. That is the major reason that you need the tool: to make the proper crimp, without too much pressure or too little. The tool works by squeezing to crimp, but at the point of greatest pressure, it ratchets back open automatically - making it impossible to crimp too hard or too soft.

    Anyway … to make the shorting jumpers, I cut 1" wire lengths, then strip 1/8" off of each end. Then I crimp on the terminals. This is the result:
    [​IMG]
    That is a perfect case of the proverbial, "one picture is worth a thousand words." I could describe how these crimp terminals attach to the wire, but seeing it above makes it perfectly clear: one lug is crimped onto the wire insulation, the other directly on to the wire.

    We're not done yet, though. The way the crimp terminals work in the housings is that there is a small bent tab on the top of the terminal that "catches" a slot in the end of the housing. This allows you to push the terminal into the housing until this tab reaches the slot. The tab springs up into the slot, so that you can't pull the terminal back out. (Use a very tiny screwdriver tip to press the tab down while pulling the wire/terminal back out, if necessary.)

    In working with the crimp terminals, that tab often gets bent back down, flush with the crimp terminal, so it won't "catch" when you push it into a housing. So, I take an X-acto knife to bend the tabs back up:
    [​IMG]

    Finally, the smooth jaw needle nose pliers helps me to bend everything back into a straight line. Again, working with the IWISS crimping tool, the crimp terminal sometimes ends up getting bent and distorted. This will prevent a proper insertion into the housing. The wire and tops of the crimp terminal should be as straight as possible across the top (except the bent up tab):
    [​IMG]

    The next step is to bend the wire in half and insert both crimp terminals into the housing:
    [​IMG]
    You can easily see the slots, in the housing above, where the bent up tabs on the crimp terminals "catch." The bent up tab is open to the right, so inserting to the left means they go in, but they can't be pulled back out (unless you use that screwdriver tip to press down on the tab through the slot).

    Once all of the above procedures are established (and re-remembered), it goes very fast. These were all done in a little less than an hour:
    [​IMG]

    Next, I test the jumpers for continuity (zero resistance), just to make certain:
    [​IMG]

    Sorry if those were excruciating details about a tiny connector. I thought it important, though, to explain the correct way to do it. Once I start on the transformers, all the rules go out the window.
     
    Last edited: May 5, 2020
  18. MichaeLeroy

    MichaeLeroy Almost "Made"

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    Thanks @TomB Please keep the not at all excruitiating details coming. I'm sure that i'm not the only one who enjoys this wonderfully thorough presentation of the T4 construction. I'm learning more than a thing or two, and that's always good.
     
  19. TheloniuSnoop

    TheloniuSnoop Friend

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    Your selection of the Molex KK connectors is spot on. They have been recommended by both Tangent and AMB for their DIY designs. I'm too cheap/lazy to get a crimper, so I've always just soldered the the wire to terminals.

    The design for changing the circuit to suit different input voltages is also brilliant. Not many manufacturers provide that, so the T4 is a refreshing departure from the 'our-way-or-the-highway' designs.
     
  20. TomB

    TomB MOT: Beezar

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    So, here we go - the last thing before casework assembly!

    As mentioned earlier, the rules for the Molex connectors go out the window when it comes to the power transformers. The reason is that even though the leads on the SumR toroids are 22ga, the insulation is 600V. So, the insulation is easily twice the diameter of the stranded wire bundle. A different technique with the Molex terminals and the crimper must be used.

    Here's a pic of one of the power transformers with the leads trimmed:
    [​IMG]

    I am not a magician. There's no way I would trim the leads on an expensive, custom-made power transformer without having developed a guide of some sort. What you see there is my cheat sheet for the entire T4 construction. On the left, I have all of the parts documented, along with their heights, and ordered in the sequence that they should be soldered into the PCB. Also in that list is the lead-bending lengths to be used with the red plastic lead bending guide (seen in the early posts) for resistors and diodes.

    Here's the section on the PT:
    [​IMG]
    It's quite a bit of information, but absolutely necessary to prevent ruining one of the power transformers. The first step, as mentioned above, is trimming the leads to those lengths in the far right column. Then the groupings of the windings guide me in what to use for the Molex housings:
    • AA-BB-CC-DD-Shield all go into a single, 5-pin housing,
    • HT-1 and HT-2 go into a 2-pin housing, and
    • LT-1 and LT-2 go into a 2-pin housing.
    Here's a pic (sorry - slightly out of focus) of a crimped transformer lead:
    [​IMG]
    What's necessary is to strip the lead so that the stripped portion is long enough to accept both crimp clamps on the Molex crimp terminal. The 600V insulation is so thick, that it won't even fit into the crimp terminal's larger lug - believe me, I've tried. So, clamping on the insulation is not an option. Crimping on the wire with both lugs requires a double crimp, because the dies in the IWISS tool are dual-sized: one for the wire, one for the insulation. This actually works quite well. If you strip and crimp at the proper length, the insulation is sized just right to press-fit into the housing. So the overall effect is still quite robust and little stress is encountered by the wire ends.

    Here's a pic with the primary leads (4 plus a shield) completed with the crimp terminals:
    [​IMG]
    All that's left is to insert these into a 5-pin housing.

    Once you get into a rhythm doing this, it goes very, very fast - faster than soldering, if you can believe it. Almost the same amount of time is taken in cutting/stripping/tinning the leads if you solder. Then you have to apply the solder and wait for the melting and cooling. None of the soldering time is needed with the crimp terminals. Here's a power transformer ready to plug into a PCB:
    [​IMG]
    Note the extremely important order of the leads in the 5-pin housing:
    1. Black
    2. Brown
    3. White
    4. Orange
    5. Green
    It's also extremely important that Green (the shield) is at the top of the connector when plugged into the headers on the PCB! You can actually reverse the order Black to Orange or Orange to Black (same windings relationship, but reverse order), but Green has to be the first connection, always.

    Being AC voltage and only two wire connections, the order with the HT leads and the LT leads makes no difference. Just make dang sure the red and yellow go in the LT housing and the blue and gray go into the HT housing! Mixing that up is a no-no!

    A test fit into a PCB (no bottom plate to mount the transformer for the time being):
    [​IMG]

    As stated, once in a rhythm with the cutters, strippers, and crimper, things go very, very fast. I finished the rest of the transformers in under a couple of hours:
    [​IMG]

    Final casework assembly begins!

    EDIT: Should've mentioned this earlier, but except for the voltage-setting jumpers, I use the Molex housings with rib wings and locking ramp. As also mentioned, it doesn't really matter except for the 5-pin housing. The rib wings and locking ramp on the 5-pin connector strongly encourages that the transformer primaries won't be reverse-connected.
     
    Last edited: May 6, 2020

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