I would always keep one meter lead on pin 4 of the chip itself and then just work back along the print using the other lead. You will have to visually look where the PCB print goes.
I would need a board in front of me to actually tell you where to probe, and working from pictures of the board layout (such as in the construction guide) is notoriously difficult without having the real thing in front of you to keep referring to.
Begin by having a lead on pin 4 and test from there to the solder pad of the socket. If that's OK then look along the print that connects to the pad and just keep testing as you work toward the power supply.
I would need a board in front of me to actually tell you where to probe, and working from pictures of the board layout (such as in the construction guide) is notoriously difficult without having the real thing in front of you to keep referring to.
Begin by having a lead on pin 4 and test from there to the solder pad of the socket. If that's OK then look along the print that connects to the pad and just keep testing as you work toward the power supply.
I'm considering putting OPA2277 op amps in my O2 to increase battery life, as I mainly use my O2 draped on the couch or slumped in the recliner (both a considerable distance from the nearest power outlet).
But I'm not entirely sure which op amps to swap out.
From what I've gathered, I believe I need to swap out U1, U3 and U4?
Do I swap in the OPA2277 in all these slots or shoul I mix it up with the TLE2062 as well?
Another concern is that this is recommended only for headphones with an impedance of 50Ohms or higher.
I'm using the O2 to power my Hifiman HE-560 which has an impedance of 45Ohms.
Will swapping in low power op amps lead to an audible decrease in sound quality?
A bit of an apropos, I'm mainly using my O2 with 6.5x gain and NwAvGuy says nothing beat the NE5532 at gains above 5x.
Does this op amp decrease battery life considerably?
-and do I also swap this op amp in all three slots if I want to try it?
But I'm not entirely sure which op amps to swap out.
From what I've gathered, I believe I need to swap out U1, U3 and U4?
Do I swap in the OPA2277 in all these slots or shoul I mix it up with the TLE2062 as well?
Another concern is that this is recommended only for headphones with an impedance of 50Ohms or higher.
I'm using the O2 to power my Hifiman HE-560 which has an impedance of 45Ohms.
Will swapping in low power op amps lead to an audible decrease in sound quality?
A bit of an apropos, I'm mainly using my O2 with 6.5x gain and NwAvGuy says nothing beat the NE5532 at gains above 5x.
Does this op amp decrease battery life considerably?
-and do I also swap this op amp in all three slots if I want to try it?
You would have to look at the data sheets on current consumption, add them all up and then compare to the O2's standard spec. The TLE2062 is an updated version of the old TL062 and while it scores on low current consumption it probably isn't a great choice here. I doubt it would match the 4556 for drive ability.
O2 Audio Issue
Hi all,
I have recently built an O2+ODACrevB using all the BOM according to NwAvGuys, only exception being the LED Avago HLMP-1301, which turns on fine. I did order the PCB board via a company using the given Gerber files.
So the problem is when doing an audio test I noticed the left channel stays on even when sound is right channel only, so using stereo audio test; left channel is on only with left test, right channel and left channel on with right test.
I have done all the troubleshooting according to NwAvGuy's guides and didn't find an issue. I'm thinking the left channel isn't being grounded properly and I'm not sure how to test it.
Anyway, thanks in advance for any adivce.
Myles Nicholls
Hi all,
I have recently built an O2+ODACrevB using all the BOM according to NwAvGuys, only exception being the LED Avago HLMP-1301, which turns on fine. I did order the PCB board via a company using the given Gerber files.
So the problem is when doing an audio test I noticed the left channel stays on even when sound is right channel only, so using stereo audio test; left channel is on only with left test, right channel and left channel on with right test.
I have done all the troubleshooting according to NwAvGuy's guides and didn't find an issue. I'm thinking the left channel isn't being grounded properly and I'm not sure how to test it.
Anyway, thanks in advance for any adivce.
Myles Nicholls
Well shoot, I got the impression from NwAvGuy's blog that it was a pretty straightforward matter of just slotting in the op amps he recommended.
-OPA2277 for low power, NE5532 for best results with high gain.
There is nothing high gain about the O2 
its all low gain (front end opamp) and unity gain (the output stages) which places limits on what actually will work successfully. Essentially any device needs to be unity gain stable.
I haven't studied in detail what the designer has said about using other devices tbh but the method of looking at the current consumption of each and comparing to the original has to be your starting point.
I've also used the TLE2072 opamp (the latest uprated TL072) and found it poor when used on low voltage supplies, specifically -/+5 volts when compared to the NE5532 and NJM2068. The available output swing was noticeably lower before clipping and this was a line stage, not a headphone amp.
So by all means experiment but also test and measure to make sure whatever you use works as expected.
its all low gain (front end opamp) and unity gain (the output stages) which places limits on what actually will work successfully. Essentially any device needs to be unity gain stable.I haven't studied in detail what the designer has said about using other devices tbh but the method of looking at the current consumption of each and comparing to the original has to be your starting point.
I've also used the TLE2072 opamp (the latest uprated TL072) and found it poor when used on low voltage supplies, specifically -/+5 volts when compared to the NE5532 and NJM2068. The available output swing was noticeably lower before clipping and this was a line stage, not a headphone amp.
So by all means experiment but also test and measure to make sure whatever you use works as expected.
Finally completed my schematic.
DC supply will be +-11.625V, 100uF will create a slow rise voltage.
Implement choices for output feedback either from NE5532 or NJM4556 (R100 & R101).
Gain will be 1.5X and 3X using Alps push button switch.
No cap in audio signal, DC bias will be about 1mV using differential amp topology at 3X gain.
4 pole 3.5mm socket, using 2 ground pin for lower impedance. Will benefit the most if headphone jack was modified for 4-pole too. See picture.
DC supply will be +-11.625V, 100uF will create a slow rise voltage.
Implement choices for output feedback either from NE5532 or NJM4556 (R100 & R101).
Gain will be 1.5X and 3X using Alps push button switch.
No cap in audio signal, DC bias will be about 1mV using differential amp topology at 3X gain.
4 pole 3.5mm socket, using 2 ground pin for lower impedance. Will benefit the most if headphone jack was modified for 4-pole too. See picture.
Attachments
Have you been able to fix this ?
I would suggest you test your O2 in isolation and make sure that L and R behave independently. I would connect your input leads (the ones you have connected to the DAC) to another source and confirm the 02 is working normally.
You should also be able to connect headphones directly to the DAC outputs via say 1k resistors and confirm the DAC is (or isn't) giving correct L and R.
As I keep saying in this thread, I have never actually built or seen an 02 let alone the DAC and so any fault-finding is based entirely on the published circuit for the 02 in this thread.
Thanks for the response Mooly, it's impressive fault-finding considering you haven't built an O2.
I have tested the amp using the 3.5mm input jack (I have the amp wired: DAC line-out --> P1 with the ground traces cut out at J1). I had the same issue with using a different source.
So I am pretty convinced it's a fault in the amp.
I have tested the amp using the 3.5mm input jack (I have the amp wired: DAC line-out --> P1 with the ground traces cut out at J1). I had the same issue with using a different source.
So I am pretty convinced it's a fault in the amp.
My starting point would be use 3.5mm input option and measure and see if the grounds are intact from the source end of the lead back to the O2's main ground. Any kind of short between the inputs would work both ways around. Floating grounds usually give rise to weird out of phase kind of sounds.
You could try feeding a normal stereo source into the O2 and then shorting C11 and C12 in turn and checking that the output from one or the other channel is 100% silenced.
Removing U1 completely should give no audio at all. Worth trying. If you find you still have audio then you have some connectivity error somewhere.
You could try feeding a normal stereo source into the O2 and then shorting C11 and C12 in turn and checking that the output from one or the other channel is 100% silenced.
Removing U1 completely should give no audio at all. Worth trying. If you find you still have audio then you have some connectivity error somewhere.
Ok so I'm starting Objective 2 amp and have searched this lengthy thread but haven't found all the answerrs.
Aelfewulf's photos provided some support, thanks aelfewulf.
1. I want to remote mount the headphone output jack- so no problem there, it's well documented, but want to remote mount the input jack, hopefully change it to a 1/4" jack also for symmetry, but not necessary, what do I need to do viz-a-viz ground etc.
Also I will remote mount the volume pot, as this is going on a metal chassis, what grounding or isolation do I need to observe?
That's it for now, thanks in advance.
Aelfewulf's photos provided some support, thanks aelfewulf.
1. I want to remote mount the headphone output jack- so no problem there, it's well documented, but want to remote mount the input jack, hopefully change it to a 1/4" jack also for symmetry, but not necessary, what do I need to do viz-a-viz ground etc.
Also I will remote mount the volume pot, as this is going on a metal chassis, what grounding or isolation do I need to observe?
That's it for now, thanks in advance.
Its really just the fault finding aspects of the standard 02 that interest me in this thread but I would just say to follow good practice when doing modifications. As to what to do with a metal case, well I would still use isolated sockets and connect the case to the O2's main PSU ground at some point to gain the benefit of shielding. All other points on the O2 should be isolated from the chassis. The volume pot (if its metal) would then be grounded as well via the chassis. The pot frame itself should have no direct continuity to any of the pins (when measuring the pot in isolation).
Thanks for that rapid response mooly.
Being a bit of a novice, I appreciate the help. With regards to grounding the psu, I take it that still applies if I'm using an external (wall wart)?
Also, when I remote mount the input jack, so I still need to remove the ground as with output jack, or is that only because it is a switched jack?
By 'grounding' I just mean connecting the metal case to the O2 zero volt line, nothing more. That just ties the case to the O2's reference of ground and gives the benefit of preventing the case picking up interference and so on.
Perhaps grounds and grounding are the wrong words here. No other connections are involved.
Hard to visualise the input arrangement but essentially you just carry the ground from the existing socket (use that existing point on the PCB) to your new socket. Also keep the lead lengths as short as practicably possible.
Perhaps grounds and grounding are the wrong words here. No other connections are involved.
Hard to visualise the input arrangement but essentially you just carry the ground from the existing socket (use that existing point on the PCB) to your new socket. Also keep the lead lengths as short as practicably possible.