The Objective2 (O2) Headphone Amp DIY Project

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If you mean will applying an audio signal to the O2 (when its not powered) cause degradation of that signal, then yes, it could well. This is because the unpowered opamps could present a highly non linear load to the source driving them.

How much of a problem that would be is hard to say. You could replace U1 in the 02 with a FET device (OPA2134 for example) and increase the input resistors (R7 and R14) by a factor of 10 and decrease C11 by a factor of 10. That would make the driving source pretty immune to whatever the O2 did. Replacing the opamp with a FET device keeps the DC offset low with the increased input resistors.
 
Hi all,

In all manuals we can see 2 methods to connect O2 and ODAC according to usage of 3.5 input socket: 1) to keep O2 input on it, 2) to change it to ODAC output.

However, ODAC has two outputs: four pins in the middle of PCB and 3.5 mm socket. Why nobody uses them both? Pins to connect ODAC with O2 and 3.5mm socket to get direct ODAC output. Does such setup affect the output quality with some negative influence of O2 input?

I was wondering the same thing, and haven't found an answer in this thread. Does anyone know?
 
Hello all, I am having problems building my o2 amp. It does not output any sound when turned on. When adjusting the potentiometer, there is a scratchy sound in the right side of my headphones. It is not the headphones, because They work fine on my souce. One of the capacitors was missing from my kit, so I bought another on of the same type, but it is not identical. I have a feeling that it is the solder joints; but I am not sure. Sorry for the low quality pictures.

http://i.imgur.com/TZrCgaY.jpg
http://i.imgur.com/mgi56Gm.jpg
http://i.imgur.com/e9MGqMk.jpg
http://i.imgur.com/xyy0okG.jpg
http://i.imgur.com/oCN2gSU.jpg
 
I have a feeling that it is the solder joints; but I am not sure.

Congratulations on getting your feet wet with soldering. :) It gets better the more joints you do and experience builds up.

Here is a place to start. Those pads in the circle are one of the power management mosfets and they have little or no solder. If the mosfets don't come on the O2 won't work. These 3 pads should look a lot more like your other 3 mosfet pads to the left after soldering.

What type of solder are you using (brand, diameter, and what composition does it say like 60/40)? I'm guessing it is fairly large diameter. You have a lot more solder on the pads than you really need. It is easy for that to happen when using really large diameter solder. You would probably have better luck with thinner solder.
 

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I have a newbie question about building an O2+ODAC. I'd like to make one which behaves more like a desktop DAC+amp+preamp, with RCA analog input jacks (for feeding the O2 by itself), the USB input jack from the ODAC, and a switch to select between the two inputs. In addition, I want RCA analog output jacks from the ODAC, which would ideally get signal regardless whether the O2 is in use or not.

Is this possible? I'm not well-versed in audio electronics, and hope to use this project as a learning experience. I had hoped that the changes I want would just be a matter of (1) using off-PCB jacks and soldering to connections on the PCB, and (2) splicing in some wires and switches. I'm worried, however, that this may not be possible for some reason, or the switches will cause signal surges down the signal chain, or some other unpleasantness.

I recently had a similar problem. I talked to JDS Labs and they're doing a custom o2/odac for me with a switched 1/4 jack, and a variable rear rca out. With a headphone inserted the rca's are muted, and when you unplug it the rear rca out is live.

The problem with O2 amp is space, there really isn't enough room for the odac, rear rca dac out, rear rca in. For that type of functionality you would need to use a seperate odac and o2 amp. That should give you enough room for a dedicated rca in/out/variable.
 
Congratulations on getting your feet wet with soldering. :) It gets better the more joints you do and experience builds up.

Here is a place to start. Those pads in the circle are one of the power management mosfets and they have little or no solder. If the mosfets don't come on the O2 won't work. These 3 pads should look a lot more like your other 3 mosfet pads to the left after soldering.

What type of solder are you using (brand, diameter, and what composition does it say like 60/40)? I'm guessing it is fairly large diameter. You have a lot more solder on the pads than you really need. It is easy for that to happen when using really large diameter solder. You would probably have better luck with thinner solder.
I am using Draper flux core solder. It doesn't say the diameter or composition, but it is fairly large, and it is probably 60/40.
 
I am using Draper flux core solder. It doesn't say the diameter or composition, but it is fairly large, and it is probably 60/40.

Good deal, that will work fine. It is probably the 1.2mm = 0.050 inch diameter I see on the internet. If you should solder up another project some day give "eutectic" solder with a 63/37 composition and something like a 0.6mm or smaller diameter a try. You will get better looking joints that will be a bit more mechanically stable.

So a suggestion... try removing some of the flux on the back of the board using isopropyl alcohol and a bunch of cotton swabs, if you haven't already. it will come off as brown stuff on the swabs. Then take a close look at all the joints using a magnifying glass. It is really hard to see solder bridges between the pins on the mosfets, voltage regulators, switches and pot without a magnifier. Any joints like the ones above just re-heat them for another second or two and add more solder so that it covers the whole PC board pad.

If it still doesn't work, post back. Mooly has been a wizard on helping folks get their O2's debugged! :)
 
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Good deal, that will work fine. It is probably the 1.2mm = 0.050 inch diameter I see on the internet. If you should solder up another project some day give "eutectic" solder with a 63/37 composition and something like a 0.6mm or smaller diameter a try. You will get better looking joints that will be a bit more mechanically stable.

So a suggestion... try removing some of the flux on the back of the board using isopropyl alcohol and a bunch of cotton swabs, if you haven't already. it will come off as brown stuff on the swabs. Then take a close look at all the joints using a magnifying glass. It is really hard to see solder bridges between the pins on the mosfets, voltage regulators, switches and pot without a magnifier. Any joints like the ones above just re-heat them for another second or two and add more solder so that it covers the whole PC board pad.

If it still doesn't work, post back. Mooly has been a wizard on helping folks get their O2's debugged! :)

It still doesn't work. One of the opamps broke, so I got a new one, and I thought that might be the problem, since it was damaged earlier; however, it still doesn't work and when I tested it some smoke came out so I think I will try again on a new board or buy one.
 
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All the parts for the O2 are easily available. For a one off you can get odd bits from Maplin.

Desoldering parts is normally quite easy but it takes a bit of practice. An iron with a large tip is usually best (as it holds the heat) and using either solder braid to "wick up" excess solder from a joint, or simply heating and pulling on the lead concerned.
 
Apologies for a totally newbie question, but I'm looking at the ODAC board and trying to understand the 4 line-out pins on it: left, right, and two more. Are the other two the ground wires? IOW, if I were to wire up RCA jacks to the ODAC, I would run one wire from L to the tip of the L jack, one wire from the R to the tip of the R jack, and then wires from the two extra holes to the sleeves of the jacks?
 
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Joined 2012
The problem here is the charging circuit of O2 is not design for charging Lithium-ion.....

That doesnt seem like an insurmountable problem to me for the higher performance you will get with lith-ion battery. Maybe someone could design a charger for it. O2 seems like a very good headphone amp. I'm suggesting you only use the best for your power source. Usually makes a positive difference.

THx-RNMarsh
 
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