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Posts by tangent

 http://www.head-fi.org/t/386517/usb-powered-pimeta  A PIMETA without buffers is a glorified CMoy pocket amp. Is that what you were after?
 Tangent Tutorial #05.  Why the plural? ("These") You should be using one dual-channel op-amp (e.g. OPA2132) and one single-channel op-amp (e.g. OPA132). If you were hoping to use two OPA2132s, it's not going to work.  They're barely usable without the buffers, at 9V. See my clipping test results. With the buffers, you might be able to drain a 9V battery dry before the op-amps start clipping. Also keep in mind that a NiMH "9V" will only be at or above 9.0 V briefly, if...
 I think it would have been simpler to just jump from pin 3 to 6 on each BUF SO-8 footprint, but buzzing it out on a bare board here says the pins you chose instead do also connect to the same locations. Your use of bare wires for jumpers is a worry. You have to be very careful that they're not touching anything. Where I have to jump over exposed metal, I prefer to use insulated wire for jumpers, stripping it at the tips only. A much bigger problem is how messy that...
The current shouldn't instantly drop in half. It will be rock steady when there is enough voltage, then roll off gently — linearly, in fact — the farther you drop below the minimum voltage.
Interesting.   Does your camera not have a way to include the temperature scale in the frame, so you can interpret the photos after losing this connection? I mean, a year later, will you remember what gray value 182 means in these particular photos?   Is the charging voltage well-optimized?  Meaning, if you dropped it any farther, would the charge current start dropping?   If you haven't done that optimization, you're making the regulator turn voltage into heat...
As for the web site itself, it's back now. (Some file permissions accidentally got reset.)   As for your PPA v2 buffer biasing symptom, that sounds like a tempco issue. I'm not sure I ever learned how a simple JFET CCS is supposed to behave as a function of temperature, but I'm pretty sure it isn't inherently tempco-stabilized. One of the whole points of this sort of biasing, though, is to force a constant current through a part specifically in order to keep temperature...
Sorry about that...file permission bug. It's fixed now.
Yes, Sparkfun, legendary house of metallurgy.    This is just another of a great number of lead-free solders. One that subs in toxic antimony for toxic lead, by the way.   I find it odd that the product page doesn't say whether the alloy is eutectic. Also, it mentions water-soluble flux as though it is purely a virtue, when in fact it's a warning sign: you must clean that sort of flux off your boards, because it is caustic.   (Reminds me of the "triple organic" sign...
 The PIMETA is primarily designed as a battery-powered headphone amplifier, so when the docs tell you that the OPA627 is known to work, well, what more did you want? :)  You need to listen to at least one of the chips with a lengthy review, then use that to calibrate what I wrote about that chip with what you hear. Only then can you hope to make good buying decisions based solely on my reviews. It's really important here, because you're talking about ~$26 x 3 = $78 worth...
By the way, it's not difficult to modify the PIMETA v2 LM317 trickle charger to let the wall supply run the amp when on wall power, bypassing the battery:       Unlike the one you show, the LM317 isn't regulating the wall power supply, so you'll want to use a reasonably clean wall supply if you go this route.
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