The Objective2 (O2) Headphone Amp DIY Project

BTW as a rule of thumb...always check resistors with you DMM before installing them, they can be bad, be off beyond tolerance or simply is not the correct value. Better be safe than sorry. A carpenter will say measure twice cut once...this applies to other fields ;)

Thanks for the advice, guys. I actually was checking the resistors with the DMM though mainly because I'm colour blind. I was certainly quite perplexed but your explanation solves that problem, I think.

I don't have a 9v bulb hence the question about what resistor to us to discharge my cheapy alkiline for battery terminal placement purposes. Presumably something on the low side?
 
Thanks for the advice, guys. I actually was checking the resistors with the DMM though mainly because I'm colour blind. I was certainly quite perplexed but your explanation solves that problem, I think.

I don't have a 9v bulb hence the question about what resistor to us to discharge my cheapy alkiline for battery terminal placement purposes. Presumably something on the low side?

If you have a car you can borrow one bulb from the stop lights...I guess most of them are 12V arent they?:xfingers:
 
OK, let's assume you have some 1/2 Watt resistors. Just to be safe and so the resistor doesn't get too hot, let's limit the power dissipated by the resistor to 1/4 Watt. P=VI, V=9 (volts), I=V/R, so 0.25=9*9/R, R=324 Ohms, so something like 330 Ohms would be a good value. The current passed through the resistor will be about 27mA. That might take a while to discharge, so add another 33 Ohm in parallel; the current through each resistor, and hence power dissipated by each resistor, remains the same, but total current is doubled and time to drain the cell is halved. Or maybe you have some 1 Watt or 2 Watt resistors, then you can use a lower resistance and discharge the battery faster. Too fast and the battery itself gets hot, I don't know enough about batteries to know what is a safe discharge rate, but something like the O2 is going to draw something like 100mA or more. Also, as the batter discharges the voltage drops, and you can use a lower resistance.

Is that enough to figure out what you need?
 
I think RS mentions that you should use discharged batteries for this purpose. I suppose it wouldn't matter so much if I hadn't already populated the board apart for the mosfets. What do you think? Risk it?
I don't recall what RS wrote. I think "should" may be overstating it a bit. With the switch off, there won't be any current flow. If there's no current flow, does it make any difference whether the battery is charged or discharged? Not to me. Not to the battery or the O2, either. What you need to be aware of is: 1) As I mentioned, make sure the switch is off and the AC adapter isn't plugged in (I'd hope you're doing that virtually any time you solder!) and 2) The battery will act as a heatsink when you try to solder, making things potentially more difficult.
Get the terminals positioned and solder only the farthest pin from the battery. At this point you only want a good enough hold so that you can disconnect the battery. After you've done that, put a good solder joint on the other 2 pins and then go back and resolder the first pin.
On second thought, reconsidering the 3-pin terminal, it's probably easiest to solder the 2 farthest pins before disconnecting the battery.
 
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FWIW, I just soldered two wires straight on to a new and live 2016 lithium cell battery for a project last week, had a bad solder joint and reflowed it and the battery got super hot... didn't hurt a thing and everything works great.

Alkaline is much safer, there's nothing that will happen that will jeopardize your safety or the O2, so even if you have an undesirable event, you'll be fine and you'll move along much faster in your project if you just connect the things and go. You've already accepted the demise of your battery... have at it. The worst that could happen is the battery might split or buldge if you short it for a LONG time. Even if that happens, you can still proceed with your project as planned. It's just an alkaline battery.
 
Well, I tried the non-discharged battery and I am unhappy to report that the consequent explosion blasted off my front porch and veranda, and moments later my eye brows fell off. I never liked that veranda, but the loss of my brows is something of a blow as I had been carefully tending them over the last month. Obviously I will have to sue the pants off everyone involved in this fiasco. I hope you have nice pants, Sofaspud and Ethanolson. I prefer corduroys.
 
I think we managed to get you on the UK's terrorist watch list; what with the explosions and uncouth brow removal technique.

Let me check...

...nope. Maybe give it a day for the block cameras to be reviewed by "staff."

But I see the backlog at the Ministry of Justice for criminal injuries compensation is rather to my favor at the moment.
 
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I have some extra O2 stuff up for auction on eBay if anyone's interested. Look for item #140732629263.

Also I have some custom engraved stainless steel front panels coming back from a machine shop right now; I'll post pictures up here once they arrive. I got two of these custom made for $34 each so perhaps I'll post the second one up on eBay if anyone's interested.
 
Well, I stuck my eyebrows back on with a bit of super-glue, so all is forgiven. And thinking about it I really don't need another pair of corduroys.

In the meantime I have a serious problem.

I reached the testing stage. It passed the resistor test. However when I did the very first test (AC power, u1-u4 out, power-switch off, test voltage at battery terminals) I got the wrong voltage, 17 instead of 23-24, and the four large capacitors warmed and slightly bulged?!?!?! I left the power in for 5 seconds at the most. I actually didn't notice the capacitor bulge/warming until after the second attempt. The bulge isn't exaggerated but my unused capacitors (I have spares) have dead flat tops.

I can barely believe it but I do seem to have hit the jackpot in terms of disaster builds.

I can think of one possible reason for this: the o2 was sitting on my anti-static mat when I did this. Presumably it's a conductor and I just shorted the whole device. I've examined the whole of the back of the board with a loupe for solder bridges but can't see any.

Any opinions as to whether it is salvageable? Presumably the electrolytic capacitors are goners. The two smaller electrolytics look fine and didn't warm up. Nor the regulators. I have two more kits for making two more o2's. But I would rather not embark on that until I've established what elementary mistake I made.