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xrk971 Pocket Class A Headamp GB
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Old 18th February 2018, 11:06 PM   #1561
tumaru is offline tumaru  Canada
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Quote:
Originally Posted by xrk971 View Post
Nice work Tumaru! You need a mint tin!
Caps upright instead of on their sides. I can't put it in the mint case. I have it on a necklace around my neck right now as a proof of concept. I might have custom wood cases made.
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Old 19th February 2018, 01:24 AM   #1562
needtubes is offline needtubes  United States
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Quote:
Originally Posted by xrk971 View Post
Would love to see your design, Needtubes. If you can offer this to the DIY community that would be great.
Got my prototype USB charger > DC boost > cap multiplier boards from OSH Park on Friday, so was able to get one stuffed and tested. Sure is tough to solder .025" pitch micro-USB connectors by hand! Everything appears to work fine, though I have convinced the board to complain audibly at times (whine emitted from the board itself). Seems the TI DC boost converter doesn't like it when the input voltage gets much higher than 5V when under heavy load. I changed one resistor value and it seems better now, though. With the part values shown on my schematic, I get 18.4V to my headphone amp which draws ~40mA, and 17V to my headphone amp which draws ~90mA. Efficiency around 80% (calculated in situ with the 40mA draw amp).

Credit for the USB charger with load sharing goes to Zak Kemble. The DC boost converter comes, essentially, from the TI datasheet, although I have changed one resistor value for slightly higher output voltage and plan to change the compensation capacitor value to see if that fixes the occasional whine. The capacitance multiplier has been seen many places, by many people, including Nelson Pass, juma, xrk971, and others (I've previously used a version with IRF510 as well). Layout is entirely my own. Board is 56.2mm x 17.2mm, so it basically fits perfectly across an Altoids tin.

Will test more fully soon, now that I've salvaged some Li-ion cells from an old laptop.
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File Type: jpg battery-supply-board.jpg (204.7 KB, 218 views)

Last edited by needtubes; 19th February 2018 at 01:27 AM.
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Old 19th February 2018, 02:09 AM   #1563
stellarelephant is offline stellarelephant  United States
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The micro USB jacks are so convenient in use, but a pain to build with. Dousing it in liquid flux and using a flat soldering iron tip did the trick on the tiny pins for me. Raptor spec'd a jack that needed to have the bottom slot tabs clipped off in order to be mounted SMD style on an OSH (no slots) board. I did this and then tacked the jack to the board using the pads on both sides. And yet a few days ago I managed to break the jack loose from the board after plugging/unplugging (carefully!) less than 30 times. Now it's just hanging by the pins and of course intermittently cutting out. If yours is also mounted this way, treat it gingerly!

Last edited by stellarelephant; 19th February 2018 at 02:12 AM.
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Old 19th February 2018, 03:03 AM   #1564
xrk971 is online now xrk971  United States
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xrk971 Pocket Class A Headamp GB
Try solder paste applied with syringe and hot plate reflow. The USB should sled solder and align fine his way.

Nice board there Needtubes!
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Old 19th February 2018, 07:03 AM   #1565
needtubes is offline needtubes  United States
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Thank you, xrk. I've tested a bit more with my Li-ion cell, and it is running fine. Will try to give it a good test tomorrow, after I give my battery a chance to charge. How long do you typically have to charge the battery using Kemble's charging circuit?

Solder paste sounds like a good idea for the micro-USB pins. I used my needle-point tip with .015" solder and managed to very carefully connect each pin.

Quote:
Originally Posted by stellarelephant View Post
Raptor spec'd a jack that needed to have the bottom slot tabs clipped off in order to be mounted SMD style on an OSH (no slots) board.
OSH Park warned me about the slots when I initially uploaded the design, so I modified the footprint for round holes instead of slots. The bottom mounting pins are functional on my boards. Hopefully that will make the connector more secure long-term, but only time will tell...

If there is interest in these boards, I can look into getting a run of them made. Or, if someone wants to "beta test" first, you can PM me about a board. I have two left, but would probably only let one go for now.
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Old 22nd February 2018, 09:34 AM   #1566
freebee is offline freebee  France
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Default XRK971 Pocket Class A Headamp not working

Soldered my kit yesterday, but it's not working. Led doesn't come on and there's no sound. Where did I go wrong? .
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File Type: jpg IMG_1832.jpg (709.3 KB, 151 views)
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Old 22nd February 2018, 01:20 PM   #1567
xrk971 is online now xrk971  United States
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Sorry you are having problems Freebee. What type of batteries are you using? Sometimes the Li-ion rechargeables need to be clicked on-off quickly 2-3 times to partially charge rail caps to prevent in-rush current shutdown of battery smart circuitry. Is LED polarity wired correctly? When no LED lights up, first thing to check is power supply or battery.

If you can measure power applied to the rail caps (circa 16v to 18v) next measure bias current through R7 array. Then current through R3. Voltage across R7 should be between 6.5v to 7.5v. Voltage across R3 should be about 3v to 4v IiRC. If 0v on R3 look for cold solder joints in main cluster of R1-R5. If voltage at gate of MOSFETs is high (same as pin 2) but voltage across R7 (pin 3) is zero, you probably have a static electricity zapped MOSFET.
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Last edited by xrk971; 22nd February 2018 at 01:27 PM.
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Old 22nd February 2018, 01:45 PM   #1568
freebee is offline freebee  France
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hi there, Just which way should the led go? Minus at the front and plus at the back? Will measure the rest as suggested. Batteries are 2x 9v Li-ion 1000 mAh rechargables. Thanks for your help.
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Old 22nd February 2018, 02:05 PM   #1569
freebee is offline freebee  France
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measured 18v on both rail caps. How do I measure R7 array? I don't get any results. R3 is 11v on both.
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Old 22nd February 2018, 02:48 PM   #1570
freebee is offline freebee  France
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I used 220R for R5 and 330R for RL (instead of 270R).
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