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Old 3rd December 2011, 05:33 PM   #1091
Turbon is offline Turbon  Sweden
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The led seems to be a part of the power management circuit so there is something else broken I'm afraid.
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Old 3rd December 2011, 05:35 PM   #1092
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Quote:
Originally Posted by robodoc View Post
Still curious about the reason why the LED stays off since the error occured.
Agreed! That is why the voltage measurements. If you get +/-12Vdc with the switch off, then your power supply is OK, at least with no load. And when you turn the switch on (all the chips still out, of course) if you get +/-12Vdc then things get interesting, since the power LED and a series resistor are right across the power supply rails after the power switch.

Also FWIW, here is a picture of the backside of one of my unmodified boards. Your solder joints are fine, but it is easy to "flood" them with solder if the solder is too big. I've actually been using 3 sizes of solder, which helps: 0.015" for surface mount and the very smallest O2 holes; 0.022" for most of the pads on the O2; and 0.050" for the bigger pads like the battery terminals and power jack. Looking at your board I'm guessing you may have used 0.050" or larger for most of the holes. The tiny tip I'm using on the iron helps a bit too, but solder size is probably a bigger factor.
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Last edited by agdr; 3rd December 2011 at 05:44 PM.
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Old 3rd December 2011, 05:47 PM   #1093
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In consideration of building a low-power/long-battery-life model I've understood that it wouldn't be able toi supply high current phones but that high voltage phones would be fine.

Am I right in thinking that high current is the preserve of planars/ortho-dynamics, and that conventional drivers only go high voltage? Perhaps not but true generally, as a rule of thumb.

Are there high current conventional driver phones?
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Old 3rd December 2011, 05:49 PM   #1094
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Are those pics of a completed board, agdr?

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Originally Posted by agdr View Post

Also FWIW, here is a picture of the backside of one of my unmodified boards. .....
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Old 3rd December 2011, 07:09 PM   #1095
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Quote:
Originally Posted by robodoc View Post
Checked then and checked now again:
All diodes are in correct direction.
The amp directions were correct too, double checked before first power on.
I will do the suggested measurements later and report on that. Still curious about the reason why the LED stays off since the error occured.
The LED is literally right after the power switch. The voltage from the LED is used by the power management comparator (U2) but the LED itself should come on even with U2 not installed. Where it's drawn on the schematic might not make it obvious, but it's literally hardwired to the power switch.

So if the LED isn't coming on, on AC power, the only possibilities are the LED itself, R6, a bad solder connection/trace, a short or something drawing way too much current (the regulators would get hot), or something upstream of the power switch which is easy enough to check if you have a DMM. Pins 3 and 6 of the switch should be close to 24 volts with the power switch on. If not, are the regulators getting hot? If so, there's a short or bad component somewhere in one or both rails to ground or shorting the rails to each other.

If there's 22+ volts across pins 3 and 6 of the power switch, check the voltage across R6, it should be about 21-22 volts. If it's the same as you measured across the power switch, the LED is either shorted, or there's a solder bridge. If the voltage is much less than 21 volts across R6, the LED has either failed open, or isn't soldered fully, or the traces to it are damaged.

You can check the voltage directly at the LED terminals. It should be around 2 volts. If it's much higher, the LED is bad (or in backwards). If it's much lower but not zero the LED is bad. If it's very close to zero the LED is bad or there's a solder bridge.

Are you using battery or AC power for your testing? One other person installed the battery terminals backwards which will also keep the LED from coming on and can damage the op amps but probably not make them explode (the otherwise high reverse current is limited by the 220 ohm resistors R1 and R2). So, regardless, make sure the "+" terminals of the batteries are the left (input side) of the board.
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Old 3rd December 2011, 07:22 PM   #1096
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Originally Posted by lorriman View Post
I need a little solder advice.

<snip>

A related question: I've been attracted to the idea of getting a smoke extractor/filter but since I'm not going to be doing this all day every day do you think that I can get away with just a simple cheap desktop fan to blow away the smoke? I don't fancy opening the door to the outdoors as a another alternative.

Thanks for any help.

And thanks to RocketScientist whose clarity and objectivity and seemingly transparent expertise are truly a delight to behold. By gum it's nice to think one is really getting some facts.
Thanks for the kind words! I try... with mixed success sometimes

You're not likely to suffer any ill effects from soldering a single O2 without a smoke extractor. If you have any sort of fan of any size or kind you can set it up somewhere to blow the smoke away from you. But people soldered all day every day for decades with the smoke in their face without too many associated ill effects. Widespread use of the extractors didn't really start until the 90's or so. So I wouldn't worry about it too much.

Any solder of approximately the right diameter with a rosin core and around 60/40 should work OK. The stuff from Mouser in the O2 parts list is fine, and cheap, if you are going to order parts from them. For all I know even Radio Shack solder might be OK these days, or something you can find at the local big box home improvement store. But there are some solders made for other purposes, and/or with really lousy rosin flux, that are not suitable or will be frustrating to use.

You don't need to spend more than a few dollars. The 1 pound spools have become really expensive--in part because there's some sort of tariff on lead now. But you just need one of the little tubes with at least a meter (yard) of solder in it. The silver solders, etc. are just a waste of money for this application.
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Old 3rd December 2011, 07:26 PM   #1097
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Quote:
Originally Posted by lorriman View Post
I need a little solder advice. I've noticed that the solder in the BOM is a measly 18g for a relatively high price; high compared to Amazon, that is.
Stay away from 60/40, use 63/37. It doesn't sound like much of a difference but 63/37 is eutectic and much better to work with. Something like this. I see you are in the UK, I have no idea where to get good solder at a decent price there.
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Old 3rd December 2011, 07:32 PM   #1098
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Originally Posted by lorriman View Post
In consideration of building a low-power/long-battery-life model I've understood that it wouldn't be able toi supply high current phones but that high voltage phones would be fine.

Am I right in thinking that high current is the preserve of planars/ortho-dynamics, and that conventional drivers only go high voltage? Perhaps not but true generally, as a rule of thumb.

Are there high current conventional driver phones?
Yes there are. A good example would be AKG K701/702s which need a fair amount of both voltage and current. Other AKG models (especially some that are no longer offered) are even more hungry.

The problem with the low power TI op amps (actually the majority of common op amps) is they have high distortion into low impedances even at relatively modest currents. The TI parts specified for the long run time version of the O2 are rated for much lower impedances than most, but their distortion still rises fairly dramatically as the load impedance drops--even at only 0.5 volts of output.

So even a headphone like the 25 ohm Denon AH-D2000, which is fairly sensitive so it doesn't need a lot of voltage or current, will still result in higher distortion than the NJM4556. That just leaves the question of will the "more distortion" be audible? And that's harder to answer. Even with the TI op amps, the O2 still has lower distortion into a great many headphones than some other well liked headphone amps.

Do you have some particular headphones in mind?
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Old 3rd December 2011, 08:28 PM   #1099
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Talking about hungry AKGs... Would the ODA be able to drive K240 Sextetts ?
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Old 3rd December 2011, 08:33 PM   #1100
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@Shamharoth, if those are the really hungry ones that are no longer made, they're on the edge of the O2's abilities. So it would come down to how loud you like it and what kind of music you listen to. On AC power the O2 is good for 7 Vrms (20V p-p) See: More Power (if you haven't already)
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