[KeithEmo]

  I like and agree with your view. My approach is to keep the O2/ODAC and keep trying different headphones. It eliminates the need to worry about up-link / chain variables since I assume that the O2/ODAC is perfectly transparent (read the measurements by the designer and other enthusiasts).
 
Especially as a student, but one who really enjoys his music, I can't say how much money this approach has saved me.

 
That is an excellent modus operandi.....
 
The differences in sound between various headphones are going to be MUCH more obvious that the differences between headphone amps (at least if you're talking about neutral sounding solid state ones). And, while trying lots of headphones can be a bit expensive, find yourself a local headphone meet and you can try a good selection for free and see which ones you like before you buy them. 

 

[raoultrifan]

   
That's where ADGR's output booster board comes in.

You're definitely right about this, Jacob.
 
Anyway, 7-8V is enough to drive DT880/600ohms and this can be achieved with a gain of 3.5-4.5X on O2.
 
Note: When driving high impedance headphones with O2 the buffer/output stage opamps might get a bit warm (almost hot I'd say, something between 50-60C); same applies for the input stage opamp. Small heat-sinks (dedicated for opamps or DIY from regular aluminum staples) and double-side thermal conductive tape or Arctic Alumina Thermal Adhesive will resolve this.

 

[deaconblues]

  is your direct connection to the phone done with an otg cable/adapter? or did you try with a random usb cable?

 
 

  I'm curious. Can you post a picture? So this means you can use the ODAC as the lineout for the phone?

It works when I do Phone > OTG adapter > USB cable > USB hub > USB cable > ODAC
A direct connection from Phone > OTG adapter > USB cable > ODAC does not work for me.
This is not the case for all DACs.  I also have a y1 DAC, and it works perfectly well on my phone without having to hide behind a hub.
My phone (Oneplus One) supports DAC output without needing any additional apps.
 

 

[castleofargh]

  It works when I do Phone > OTG adapter > USB cable > USB hub > USB cable > ODAC
A direct connection from Phone > OTG adapter > USB cable > ODAC does not work for me.
This is not the case for all DACs.  I also have a y1 DAC, and it works perfectly well on my phone without having to hide behind a hub.
My phone (Oneplus One) supports DAC output without needing any additional apps.
 

that's so weird. the hub is powered only by the phone yet that changes something. maybe the phone messes up something when it identifies the peripheral?
 wow. mind blown, I have no idea why this happens(of course it makes me twice as curious to find the answer).

 

[deaconblues]

I think the phone refuses to power the DAC if it asks for more current than what the phone's software allows.  Using the hub tricks the phone into providing power.  There is an article offering a more detailed explanation at JDS Labs http://blog.jdslabs.com/?p=838

 

[sanakimpro]

From what I've read on JDS's website, the ODAC Rev B has fixed reliability issues and 16/88.2kHz compatibility. My unit from Epiphany Acoustics bought last December has no problems at this stage like the USB issue, etc.
 
Is there any audible difference between the O2/ODAC rev B with the original O2/ODAC?
 
Thank you!

 

[diamondears]

Is it normal for an O2/ODAC Combo to make a popping sound through the headphones when the power button is pressed?

wiggle the connectors gently (at input / output) and then try the headphone itself. If that don't work disconnect and re-connect. If that don't work, try other 3.5mm cables / headphones.

I find the 3.5mm connectors are a little cheap and I often have the L channel cut out and have to give mine a little wiggle every now and again.

My oldest O2 have this. I have to wiggle the connectors to resume sound. I found out that the problem is the thin wire (what's this for?) looped around the screw at the bottom of the O2. I suppose the screws loosened a little and the wire got unlooped on the screw. I just loosened the screws, re-looped the thin wire and made sure it got trapped by the screw.

If this is your problem, it might solve both your issues.

 

[WilliamLeonhart]

   
 

It works when I do Phone > OTG adapter > USB cable > USB hub > USB cable > ODAC
A direct connection from Phone > OTG adapter > USB cable > ODAC does not work for me.
This is not the case for all DACs.  I also have a y1 DAC, and it works perfectly well on my phone without having to hide behind a hub.
My phone (Oneplus One) supports DAC output without needing any additional apps.
 

Well at least it workds... But that's too cumbersome and (for me) defeats the purpose of connecting the DAC to the Phone

 

[xxxfbsxxx]

  Well at least it workds... But that's too cumbersome and (for me) defeats the purpose of connecting the DAC to the Phone

then use this http://www.ebay.com.au/itm/321540091516?_trksid=p2060353.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT 
or try ebay with keyword "OTG injection power adapter"

 

[MrMateoHead]

My oldest O2 have this. I have to wiggle the connectors to resume sound. I found out that the problem is the thin wire (what's this for?) looped around the screw at the bottom of the O2. I suppose the screws loosened a little and the wire got unlooped on the screw. I just loosened the screws, re-looped the thin wire and made sure it got trapped by the screw.

If this is your problem, it might solve both your issues.

Wow thank you for sharing this - I will pop open the case later on and see what I find. It would be great to get rid of my little "channel drop" issue as I adore this amp.

 

[MrMateoHead]

My oldest O2 have this. I have to wiggle the connectors to resume sound. I found out that the problem is the thin wire (what's this for?) looped around the screw at the bottom of the O2. I suppose the screws loosened a little and the wire got unlooped on the screw. I just loosened the screws, re-looped the thin wire and made sure it got trapped by the screw.

If this is your problem, it might solve both your issues.

#1 Here is the small thin wire (sry my camera sux - a lot)
 
 
 
Hard to make out, but this screw hole was obviously ground out - the small thin wire must be a chassis ground for the input connector.

 
And for those that have not taken apart an O2 before, here is the 1/16 allen key for putting the volume knob back on. Make sure you allow a smidge of space between it and the faceplate, when I didn't, they ground together a bit. Also, I found that keep ALL screws loose until you had each screw started was a good idea, otherwise, they were not going in easy / straight.

 
I didn't try THAT hard to place the wire onto the bare metal, bending it only slightly for better contact when the plate went back on. So far, it appears to have done the trick though - I've played with the input connector and, to my surprise, no channel cut outs. Unfortunately I noticed during this process that one of my batteries latches on to its connector well, and the other is quite loose. Seems a piece of foam or some sort of spacer might've been a good idea for these as the batteries may dislodge slightly when dropped. Later I'll probably shove some foam I have kicking around in there to provide a little support - unless someone tells me not to. Thanks Diamondears!

 

[deaconblues]

That little wire loop is just for connecting the amp's ground to the case in order to help reduce the chances of electrical noise.  I don't see how it could affect connectivity with the headphones and/or input jack.  The most likely scenario is that the cheapo jacks on the O2 are worn out.  This is especially likely if you are using a solid 1/4" to 3.5mm adapter.  That puts a lot of stress on the headphone jack.  I've ruined 3.5mm jacks with those things before.
 
I'm currently using a Sennheiser 1/4" to 3.5mm adapter, which has a short length of wire between the 1/4" input and the 3.5mm output.  Hopefully this will never stress the headphone jack enough to cause connection problems.  If my headphone jack ever starts acting up, I'm gonna do some surgery and replace it with a  1/4" jack.

 

[MrMateoHead]

  That little wire loop is just for connecting the amp's ground to the case in order to help reduce the chances of electrical noise.  I don't see how it could affect connectivity with the headphones and/or input jack.  The most likely scenario is that the cheapo jacks on the O2 are worn out.  This is especially likely if you are using a solid 1/4" to 3.5mm adapter.  That puts a lot of stress on the headphone jack.  I've ruined 3.5mm jacks with those things before.
 
I'm currently using a Sennheiser 1/4" to 3.5mm adapter, which has a short length of wire between the 1/4" input and the 3.5mm output.  Hopefully this will never stress the headphone jack enough to cause connection problems.  If my headphone jack ever starts acting up, I'm gonna do some surgery and replace it with a  1/4" jack.

No likely for me as I've only owned mine for about 2 years and rarely mess with the input or even switch out my headphones.

 

[WilliamLeonhart]

  then use this http://www.ebay.com.au/itm/321540091516?_trksid=p2060353.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT 
or try ebay with keyword "OTG injection power adapter"

THANKS! It's cheap too, seems great for my Nexus 7!
 
But I'm using an iPhone too...

 

[rick900]

Hi guys bit confused here I ordered the o2/odac rev b combo and there is no usb port at all on the unit for the cable it came with, am I right in saying I have been sent only the amplifier? 
 
 
 
http://imgur.com/sRmaCbV