New DIY Altoids Tin Amp - The Pocket Class A "Wintergreen Handwarmer" by xrk971

  1. xrk971
    I guess you did not read the thread - normal issue with EBL's smart self protect circuit cutting off power due to turn on transient. The rail caps suck a lot of current upon initial turn on and the battery has a smart circuit that thinks it is a short. Solution is to turn on/off quickly and about 2-3 clicks it should stay on as each cycle charges caps more until they don't draw too much.

    Some EBLs are DOA. I have had to return several.
     
  2. gwompki
    Oops! Between reading this and the thread on DIYA I'm sure I have forgotten a lot. Thanks for the quick reply. That solved the issue. Thought I was going crazy.
     
  3. funch
    Are you doing the on-off-on-off-on procedure?

    Dang 'X', you were too fast on the keyboard.
     
  4. stellarelephant
    What X and Funch said.

    Also: If you tire of the multiple on/off workaround, the OKCells I use don't have this issue, and give a little extra voltage to boot, though runtime is a little less, at just over 2 hours. Quality control isn't perfect. I have had one cell out of four go bad after less than ten charges. The others are plugging right along though. Also note that these put out just over 18V and probably deserve 20V or 25V power rail caps.
     
    Last edited: Jul 11, 2017
  5. gwompki
    Thanks guys! It's pretty amazing the audible difference going back and forth between the fully charged EBL and Duracell that are down to 7.1V.
     
  6. xrk971
    So in a way, the OK cells may not last as long, but during their 2 hr life, the output is consistently high. I have not measured them for noise, I suspect there is some as there is a DC step up converter but its probably noise high above audio band.
     
  7. stellarelephant
    So I did a test fit and discovered that it is impossible to populate the PCA board with 12.5mm wide caps on both input and output, and still have room for two 9v batteries in the tin. I was crossing my fingers and everything, but no dice.

    This means that if I want to use a big fat output cap like Funch did, I have two options. One is to use a smaller 10mm wide power rail cap like he did. But I already soldered in a 12.5mm wide Panny on the power rails, and I like it. The second option is to make the batteries smaller!

    IMG_2255.JPG

    Popped one open, and was surprised at the size reduction. The actual cell is small enough that I could probably fit four of them in the tin...but using two, I'll have plenty of room for big caps to hang out over the edge of the PCB.

    Another advantage is that I ought to be able to glue the micro USB ports flush with the tin surface now, which was impossible before. I had to cut large messy holes in the side of my first tin to accommodate the full diameter of the male USB plug housing. Now I can probably just keep it neat with a hole punch.

    But of course this begs the question, isn't there a better way entirely? It would be awfully nice to be able to charge my amp with a single USB cable instead of two. And even nicer if the battery capacity was larger. It is now quite obvious to me that a much larger cell could fit in the tin, probably doubling runtime, at least. X, do you have any insights or recommendations for adding a purpose-made battery and charging circuit to this amp? I really like the full 18V power, by the way :)
     
  8. gwompki
    Very cool stuff! I like where this is headed.

    I wonder if a larger enclosure would help accommodate different batteries and associated charging circuitry. Actually I would love to see the PCA in a more permanent enclosure. I have to fly tomorrow and as much as I want to bring the PCA with me, I'm terrified of it being confiscated (or worse) by TSA. Anyone flown with one before?

    The little bear B4 is a very manageable size imho ...I'm willing to sacrifice my chassis for experimentation to fit the PCA if someone wants to take on that project.
     
    Last edited: Jul 14, 2017
  9. stellarelephant
    Lol yeah I guess they might look a little suspicious. Never seen that little tube amp before. Handsome. But I guess the PCA must slay it in terms of SQ if you are considering stealing its case!?!

    Honestly I sorta love the humble DIY aesthetic of the Altoids tin. And after seeing the piddly size of the bare 9V cells I'm currently using, I think there is room for a much bigger battery in the tin. I just have zero knowledge of how to make it happen.
     
  10. gwompki
    You're correct...the B4, while solid with the right OpAmp, just doesn't compare to the PCA. Those little sub-mini tubes definitely impart a good bit of tube flavor, which is nice, but side by side with the PCA the sound signature seems flat and lifeless.

    The PCA is so nice and compact you could probably fit a micro DAC in a larger enclosure as well lol.

    I agree in terms of the diy aesthetic...it is a lot of fun. I might try my hand at fitting the PCA in the other enclosure one of these days just for travel purposes.
     
  11. xrk971
    If you cracked open the Ok cell, you will see it uses a 800mAhr 3.6v LiPo. Look on eBay for a 3000mAhr LiPo and swap them out. The old charger and step up should handle everything for you. The cells you buy typically have a built in smart auto protect to prevent over charge, over discharge, and shorts.

    You can also make your own from scratch with a DC step up and a USB charger. Nice thing with your own DC step up is you can set it for 18v from 3000mAhr. 18v/3.6v And that gives you equivalent 600mAhr battery.
     
  12. stellarelephant
    X, you make it sound so easy! So do you think one of these cheap adjustable step ups would work? Would I need to worry about noise?
     
  13. xrk971
    That's exactly what I use. You may. Need an 0.47R series resistor after step up so it doesn't doesn't shut down with turn-on transient. You can find them for $0.40 ea on eBay. Get extra as they blow up when you turn pot too far. I have smoked a few already. Literally flames from the the little IC. But once setup right is very reliable. 1.2Mhz switch frequency so not audible. I use a RCRCRC with 3.3R and 2200uF.
     
  14. stellarelephant
    Nice. I'm sorry if you have explained all this before (I think you did discuss this in the complete PCB thread maybe?). The RCRCRC filter with 6600uF total seems like it'll eat up some serious space! The EBL and OKCell 9V LiPo batteries we are using don't have a filter like that built in, do they? I guess I'm wondering why I would need it with a single large cell if it isn't necessary with the two smaller ones. Or are you just conditioning the power to a degree that is far superior to what two purchased 9V LiPo cells can produce?
     
  15. stellarelephant
    Wow, even with the cheapest Digikey shipping, my order came in two days! Got some more members of the Nichicon lineup here to evaluate.
    Why didn't I remember to charge my batteries last night? Lol. Waiting anxiously...

    IMG_2258.JPG

    16V 470uF FG / 25V 330uF FG / 25V 1000uF FW / 25V 1000uF KW

    All identical 10x20 can sizes, but different values. I'm basically trying the biggest caps from each series that'll fit my board. I may end up using a lower capacitance value if overall SQ justifies it...even if that means a tiny bit of bass roll off with my 50 ohm cans. I'm even going to audition a 220uF Silmic when my PartsConnexion order arrives. I'm going to let my ears be the final judge, and I believe different caps do have different bass quality outside of simple capacitance value, but here are predicted bass responses for the different values I'm trying. I have a 1K resistor at RL in parallel with the 50R headphone load, so the total load is 47.6.

    bode5.jpg
     

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