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Old 4th December 2011, 01:07 PM   #1121
agdr is offline agdr  United States
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Quote:
Originally Posted by robodoc View Post
The LED is bad, I finally soldered it out and replaced by one from another set I have here. Fine to see the new LED is doing the job!

I still have serious concerns what happened to make the opamp pop. Do you have any hints what I shall prove again before connecting headphones? I can't see any obvious faults on soldering or component disorder.
Good work on your troubleshooting! That LED must have either been bad from the start or possibly static damage during assembly. LEDs are pretty tough though. I can't remember the last time I killed one. Probably just defective.

RocketScientist is the best one to assist with the blown chip issue. I can't think of any link between the bad LED and the blown chip. All the bad LED would do is jam the power management circuit "on" all the time.
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Old 4th December 2011, 01:40 PM   #1122
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robodoc - I just went back and read your original posting again. It sounds like the LED was originally working OK, but then died at the same instant the NJM4556 exploded.

The Objective2 (O2) Headphone Amp DIY Project

Interesting! Definitely will take RocketScientist to figure that one out. Even a pretty healthly voltage spike on the rails shouldn't take out the LED since it has the series current limiting resistor.

Last edited by agdr; 4th December 2011 at 01:44 PM.
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Old 4th December 2011, 02:14 PM   #1123
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i'm thinking of doing a long battery-life desktop version of the O2 and wondering how limiting that would be. I know it sounds crazy but providing for a niche is always highly satisfying, and it's not truly mutually exclusive. Because the op-amps are pluggable there's no real risk any way. On that note: I was wondering how much the long-battery-life resistor recommendations might add on top of the 20-30 hours? Is it worth the bother? As it happens I wouldn't know what resistors to get anyway, but I was thinking of exploring the possibility although it would seriously limit the device, of course. But the exclusivity would be marvellous.
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Originally Posted by RocketScientist View Post
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 4th December 2011, 02:50 PM   #1124
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Originally Posted by cheapskateaudio View Post
Thank you, how did you get that case temperature?

I have .615 watts dissipation based on my measured numbers. My unregulated voltage is over 24 volts.

The amp draws 35ma, and the regs have 15ma at the outputs.

Uncased, I measured the regs at 77C after an hour or so.
I have both contact and IR thermometers--both by Fluke and very accurate.

I don't know what "draws 35ma, and the regs have 15ma at the outputs" means. They should be the same number. And if your amp is drawing 35 mA idling with no batteries, something is wrong or your mods have really messed up the amp.

At 35 mA and 24 volt unregulated, you get 24-12 = 12 volts drop and .035*12 = 0.42 watts not 0.615 watts.

The junction temp rise would be, worst case, 0.42 * 60 = 25C. So even with a warmish ambient of 30C that gives 55C junction temp. By definition the case temp has to be lower than the junction temp. Your 77C is way out of line. So either something is wrong with your measurements, your regs are damaged and dumping a bunch of current through the ground terminal (very unlikely), or you need a better thermometer.

As they have posted, many others are using the O2 with the HD650 and similar headphones, including me, and are very happy with the sound and nothing gets uncomfortably hot or overheats.

I suspect one or more of your mods has messed up your amp. It may well be oscillating at ultrasonic frequencies which would explain your bad sound complaints and high current draw. I would suggest restoring it to the default "stock" build and then you should get the same great performance as the rest of us. If not, there's still an error with your build.
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Old 4th December 2011, 02:51 PM   #1125
robodoc is offline robodoc  Germany
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Originally Posted by agdr View Post
robodoc - I just went back and read your original posting again. It sounds like the LED was originally working OK, but then died at the same instant the NJM4556 exploded.

The Objective2 (O2) Headphone Amp DIY Project

Interesting! Definitely will take RocketScientist to figure that one out. Even a pretty healthly voltage spike on the rails shouldn't take out the LED since it has the series current limiting resistor.
Yes thats the way the things were going.
But ... now with new LED and both NJM4556 exchanged to new ones the o2 works like hell .... MUSIC!!!

Still have no idea what happened with those parts, if one of them was defect or damaged by installation or something else? Now its working, so obviouslyI did no soldering errors etc. Maybe RocketScientist will find an explanation. I'm not into that electronics so much to interpret this special case.

Big big thanks to agdr and RocketScientist for the helpful hints and THANKS to all of you for assisting my troubleshooting.
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Old 4th December 2011, 03:00 PM   #1126
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Originally Posted by lorriman View Post
i'm thinking of doing a long battery-life desktop version of the O2 and wondering how limiting that would be. I know it sounds crazy but providing for a niche is always highly satisfying, and it's not truly mutually exclusive. Because the op-amps are pluggable there's no real risk any way. On that note: I was wondering how much the long-battery-life resistor recommendations might add on top of the 20-30 hours? Is it worth the bother? As it happens I wouldn't know what resistors to get anyway, but I was thinking of exploring the possibility although it would seriously limit the device, of course. But the exclusivity would be marvellous.
The gain stage resistor change will only help battery life a small amount but it may lower distortion slightly under some circumstances. The downside is slightly higher noise. The easiest change is to approximately triple the values of R16, R17, R19, R21, R22, R23. That provides an easier load for U1 to drive. You have to change all six of those resistors.

The biggest issue is still what headphones you want to drive. If they're 50 ohms or above the low power version should work fairly well. And under those conditions, increasing R10, R11, R15, and R18 to 10 ohms will improve battery life still further as it will reduce quiescent DC offset current between the op amp pairs. The output impedance would be 5 ohms which is still fine for any (non balanced armature) headphones 40 ohms or higher.
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Old 4th December 2011, 03:04 PM   #1127
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Originally Posted by robodoc View Post
Yes thats the way the things were going.
But ... now with new LED and both NJM4556 exchanged to new ones the o2 works like hell .... MUSIC!!!

Still have no idea what happened with those parts, if one of them was defect or damaged by installation or something else? Now its working, so obviouslyI did no soldering errors etc. Maybe RocketScientist will find an explanation. I'm not into that electronics so much to interpret this special case.

Big big thanks to agdr and RocketScientist for the helpful hints and THANKS to all of you for assisting my troubleshooting.
You're welcome. Glad it's working! There are lots of possibilities as to what may have gone wrong. It might have been something as simple as a lead clipping that was laying under the PC board when you first powered the amp up. Such a clipping can create a nasty short and easily damage components with just a slight move of the board while testing or using the amp.
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Old 4th December 2011, 04:39 PM   #1128
qusp is offline qusp  Australia
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I read someone on headfi is running AD797 in this how does one even do that? with 2 x double soic8 adapters? without proper compensation i can only imagine what that looks like on the scope
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Old 4th December 2011, 04:59 PM   #1129
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I think it's just a matter of perception. How hot is hot? Do you have to pull your finger of them as soon as you touch them for fear of getting burned, or are they just hot shower hot?
They don't get hot enough to "hurt." More like hot shower hot as you said lol. What would be the expected component life span of the regulators through every day use for a few hours(maybe a worst case scenario)?

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Originally Posted by RocketScientist View Post
What AC wall transformer are you using? With 12 VAC the regulators should be warm but not hot. With 16+ VAC they get hotter, especially if the batteries are also installed and charging or the amp is playing loud into difficult headphones.

With the WAU16-400 16 VAC transformer, the unregulated voltage is 23.1 VDC so Vdrop = 11.1V. That gives 0.61 watts total dissipation and a rise of 37C above ambient or 62C junction temp with a case temp around 50C (122F).

With a 18 VAC transformer Vdrop is 14V giving .77 watts and 46C rise or 71C junction temp.
I'm using the wau16-400 so those temperatures seem too be right. I have a temperature probe in my lab I could use but I'm not sure how accurate it will be. What I'm also unsure of is why did I measure a few volts over the adapter rating on it's output. Is that the "unloaded" voltage?
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Old 4th December 2011, 05:08 PM   #1130
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@dewesiuk, you are correct about the unloaded voltage. And the regulators may outlive you running at a 60C junction temp for a few hours a day. A lot of commercial gear runs parts much hotter than that. You don't even want to know what some of the junction temps are in a typical 55 inch LCD TV. Pioneer had an entire series of stereo receivers that ran the regulators so hot the PC board (over several years of the receiver being stacked with other gear and stuffed in a hot closed equipment rack or similar) degraded, turned black, and eventually the pads on the PC board failed before the regulators did.

For those wondering, I took a class on DFR--design for reliability. It was taught by the head of engineering for one the biggest DFR consulting firms in the country. He had lots of interesting stories to share.
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