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Old 10th April 2013, 08:38 AM   #3221
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The gain-setting resistors are open circuit without the connection to ground, so you're probably getting 1x gain.
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Old 10th April 2013, 01:22 PM   #3222
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Alright. Now I just need to find a new gain switch. The problem is not finding one, the problem is finding a place that doesn't have 20€ shipping...
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Old 12th April 2013, 05:43 AM   #3223
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Quote:
Originally Posted by Rullknufs View Post
Alright. Now I just need to find a new gain switch. The problem is not finding one, the problem is finding a place that doesn't have 20€ shipping...
Without gain switch installed(with no solder bridge or pcb trace damage), gain is 1X. If you are stuck I can send it from India (4 switches for 1$ plus postage, everything in bubble wrap envelope- approx. 15 days delivery time). Sending by Indian postal service is very economical.
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Last edited by availlyrics; 12th April 2013 at 05:47 AM.
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Old 12th April 2013, 06:25 AM   #3224
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Quote:
Originally Posted by availlyrics View Post
Without gain switch installed(with no solder bridge or pcb trace damage), gain is 1X. If you are stuck I can send it from India (4 switches for 1$ plus postage, everything in bubble wrap envelope- approx. 15 days delivery time). Sending by Indian postal service is very economical.
Thanks for the offer!

But Stefan at Headnhifi is already sending me some.
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Old 12th April 2013, 08:51 AM   #3225
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Good ol' Stefan, always helpful
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Old 14th April 2013, 08:08 PM   #3226
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um, Hi... Not sure if this is the right place to ask this, but since I'm about to just toss my o2 amp in a box in the closet and move on with my life I thought I would give it a try...

I built the amp nicely, not troubles (that I know of) went through the testing and it seemed fine. plugged in some cheap headphones and voila, Bob Marley...

But then I noticed something totally weird... I was getting what sounded like both left and right signals in both ears. I AB'd it with another amp, listened to what was coming from the dac, listened with different sources, different headphones, tested cables adapter and... yup, both ears had left and right (causing "phasey yukness") and destroyed the stereo field "soundstage" and left me with a really beautifully loud and amazing low end what seemed like an awesome but messed up amp...

That was the first problem... I went through the testing again and again and scoured all your forums (I say your because this is my first post here)... In the time I've spent trying to troubleshoot this thing I could have built 5 more amps and maybe one of them would be working by now lol...

Anyway in the process of trying to figure out what is wrong with this amp I must have shorted the U2 chip and now the thing is dead. no light, nothing.

Now I'm pretty sure I can find the fried part and order another chip and get it going again, but what was wrong with it in the first place. I would love to know what would make it play out of both channels like that before order another one and try again (which I plan to do because I didn't really get to hear how the amp sounded and I really want to check it out).

And it had very low distortion even a high levels, sounded pretty great and didn't have any missing elements, just no stereo field...

I screwed it up somehow, but I would really love to know what was wrong with it before I spend the rest of my life troubleshooting 30 parts...
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Old 15th April 2013, 03:09 AM   #3227
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Sounds like a solder bridge at the sound jack... either input or output jack. I'm guessing input but that's only a guess.
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Old 15th April 2013, 04:21 AM   #3228
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I looked and tested and don't see any but you're probably right. I'm going to take them off and go desktop style at this point... Hopefully I can find the part I fried shorting the U2 chip and bypass the input and output jacks and it will function properly. Sure is a neat little amp... Thanks for your help
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Old 16th April 2013, 04:51 AM   #3229
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Quote:
Originally Posted by KrisCode View Post
Anyway in the process of trying to figure out what is wrong with this amp I must have shorted the U2 chip and now the thing is dead. no light, nothing.
You can use NE5532 as U2(RS suggested NE5532 can be used if JRC2903 is NA) or can even bypass PM circuit completely for testing purpose. My guess is you might have ruined the MOSFETs and not U2 as ICs are pretty robust.
That "phasey" sound is because your i/p or o/p ground connection is "floating" i.e. not making proper contact. You might have got faulty i/p or o/p jack.A few post back someone had mentioned the same problem.
And yes this is the right place to ask all O2 related issues.
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Last edited by availlyrics; 16th April 2013 at 05:03 AM.
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Old 20th April 2013, 06:24 AM   #3230
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I don't know if anyone else has observed this, but I have channel imbalance problems with my O2 at low levels. It's fine at higher volumes, but I don't like to listen too high especially with IEMs, and at listening volumes, it actually is an issue at times.

I've narrowed the issue down from testing and logic to the potentiometer... it seems the Alps RK097 pot might just not be that great. Can someone tell me if it would be okay to swap in this pot to test if this solves the issue: PTD902-2015F-A103 Bourns | Mouser

In theory it should fit, but in theory and in practice are often to different issues. Thanks!
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