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Old 14th December 2012, 06:53 PM   #2951
Laike is offline Laike  Canada
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Will I be able to have some one just resolder the MOSFETs in the correct manner? Or will it need a complete replacement of the MOSFETs. I think the wisest course of action for me is to request a partial refund from the seller to cover repairs for the amp.
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Old 14th December 2012, 08:38 PM   #2952
agdr is offline agdr  United States
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Quote:
Originally Posted by Laike View Post
It was pointed out to me that the U5 and the U6 MOSFETs have been installed backwards and the C6 and C7 capacitators may be the wrong types
Those are the voltage regulators, U5 and U6, that are backwards not the mosfets. The mosfets look OK from the photo. C6 and C7 look like MLCC rather than film but it shouldn't matter.

The pinouts are different on those regulators. The positive regulator, MC7812, may have survived since input and output were swapped. Maybe not so much for the negative regulator, MC7912, because that would swap ground the output. If it were me I would replace both with new chips. LM7812 and LM7912 would work just fine.

The regulators will come right out if you take a piece of copper desolder braid a half inch long or so and place it across all 3 pins on the back of the PCB, then heat the braid with your soldering iron so all 3 pins get hot at once. Support the PCB so the part with the regs has nothing underneath so the regs can fall out. The holes in the PCB are big enough that gravity will cause them to drop right out onto the ground once the solder on all 3 pins melts. Actually kind of fun, I've done it a few times, lol.

Check that the regulators were in the right spots, too, once you get them out. The negative MC7912 is the one closest to the edge of the PCB.

Another issue is the output chips in your photo, the two in the middle, are the low power TLE2062CP option on RocketScientist's BOM rather than the standard higher current NJM4556s. The TLEs are fine, but can't drive nearly as much current to the headphones as the NJMs can. Plus have slightly more distortion, although it probably isn't audible. The details are in RocketScientist's blog here http://nwavguy.blogspot.com/2011/08/...lowpoweroption

Last edited by agdr; 14th December 2012 at 09:03 PM.
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Old 14th December 2012, 11:32 PM   #2953
agdr is offline agdr  United States
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Laike - I just realized your imgr link had 4 more photos of the PCB in the gallery. In the last photo the gain op amp behind the volume control, the JRC2068, doesn't look to be seated flat on the socket. A pin may be bent underneath. Try carefully to push it down. If it won't go pull in out of the socket to make sure no pins are bent.

I didn't see your other post before. That 12Vac 200mA transformer is only a good idea if you are sure your AC line voltage is (higher end of the range) 120vac - 130vac (here in the states anyway) and your headphones don't pull more than about 5 - 10mA or so if you are also charging batteries at the same time. I've posted a long rant about it in the head-fi O2 headphone amp thread if you want the details. If you are going to place a Mouser order anyway for the regulators or NJM4556 chips you might as well get a WAU16-400 or WAU16-1000 transformer (the BOM alternates) while you are at it and toss the 12vac/200mA in the wastebasket (just my opinion here).

Good luck!

Last edited by agdr; 14th December 2012 at 11:38 PM.
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Old 15th December 2012, 12:06 AM   #2954
Laike is offline Laike  Canada
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agdr, thanks for your posts. I think its pretty obvious at this point that this amp isn't worth the trouble of grabbing a friend to do the repairs for me. If I could solder, I wouldn't mind requesting the partial refund and doing the repairs myself, but due to hand tremors, soldering two wires together is already a pretty dangerous task for me, let alone the PCB board. I'm going to request a full refund or for the guy to cover the full costs of repairs from a specialist. Thanks for your time and effort in all of this.
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Old 15th December 2012, 05:16 AM   #2955
qusp is offline qusp  Australia
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lol, that'll teach me to not look at the schematic, many will know my O2 PCBs are still virgin. of just about all the parts the fets seem to be the most vulnerable from builder responses

Last edited by qusp; 15th December 2012 at 05:19 AM.
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Old 15th December 2012, 07:14 AM   #2956
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Quote:
Originally Posted by Laike View Post
agdr, thanks for your posts. I think its pretty obvious at this point that this amp isn't worth the trouble of grabbing a friend to do the repairs for me. If I could solder, I wouldn't mind requesting the partial refund and doing the repairs myself, but due to hand tremors, soldering two wires together is already a pretty dangerous task for me, let alone the PCB board. I'm going to request a full refund or for the guy to cover the full costs of repairs from a specialist. Thanks for your time and effort in all of this.

If you had a builder, then mistakes were made. A specialist however is not needed. An amateur like myself was able to populate the pcb so it doesn't take a rocket scientist. Just attention to detail.
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Old 15th December 2012, 05:28 PM   #2957
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Indeed, no specialist needed. If we lived closer to eachother I could easily fix it, and I'm a beginner (built a couple of O2 amps though). Maybe you have any friends that can solder?
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Old 22nd December 2012, 03:10 PM   #2958
archro is offline archro  China
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Very appreciate Mr.RS's effort on O2.AMP!

I build one by myself in China. the O2 sound is fantastic. I am very like it. low cost but the performance is not low at all, there are many many lies in audio industry, one you need pay a lot for high performance sound. I am on same side with RS, I don't believe human ear can hear the difference between a normal power cable and a Hi-End cable that maybe cost hundreds dollars.

I'd like to encourage the peoples who still hesitant if you want build an O2 AMP by yourself, you don't need any knowledge or background on analog circuit, Mr. RS already did everything for you. the only thing you need is careful, when you put components on the PCB. and some solder practice.

But I still have some questions about the O2 AMP, I am very appreciate if someone open discuss.

In my view the current O2 design is a portable and desktop mix version. I like a portable AMP more, so I'd like to know, is there way to MOD the O2 to make it more like a portable AMP, it work with Li-ion battery and DC battery charge circuit. sounds this requirement is more like a new version AMP.
Actually I accept the current Ni-Mh battery design, but my concern is it keep to charge the battery and wont stop even battery is full if we plug the AMP to an AC adapter.

If we use Li-ion battery we can share a same charger with cell phone, even charge the battery by the computer USB.
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Old 23rd December 2012, 09:27 AM   #2959
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Hi Archro - there was a discussion about using Li-ion batteries early on in the project, but the difficulties of charging them safely ruled them out. Get the charging circuit wrong, and they can explode! It's much easier to charge NiMH batteries safely, making them more suitable for inclusion in a device that's intended to be built worldwide, by people of vastly differing experience.
If you were going to modify the circuit to include Li-ion batteries, it would be necessary to include extra electronics to monitor the charge state and charge history, along with the necessary microcontroller - much more complicated and expensive to build.

There's no way to modify the circuit to charge from USB, the voltage is too low.

Last edited by greenalien; 23rd December 2012 at 09:31 AM.
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Old 25th December 2012, 12:24 PM   #2960
archro is offline archro  China
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Hi Greenalien, thank you for your replay.
I know we cannot use USB to charge current equipment.
for the Li-ion battery, I think there are billions people use this battery in the work, most of them no EE background, but I am totally understand your concern.
so is there any way to mod the charge circuit to add an auto-stop function.
I have a new question after build.
I use 0.22uf for C6 and C7 because this is what the diagram shows, but in the BOM file there are 1uf Cap. so I'd like to know whic Cap should be better.
also my C6 C7 CAP are film caps, does this matter?

thank you for your any replay.
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