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Old 7th January 2013, 08:27 PM   #3011
agdr is offline agdr  United States
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Quote:
Originally Posted by cruncynutcornflakes View Post
I can't be 100% sure but I am fairly certainly that music playing on the left channel on my headphones is louder than the right?
To track down the imbalance it would help if you could disconnect the left channel wire from the ODAC on the O2 end, then jumper over the right channel connection to the left channel connection with a short jumper wire. That way you are feeding the right channel from the ODAC to both the right and left channel on the O2. Both channels then should sound exactly the same if the problem is the ODAC, otherwise the problem is with the O2.

The volume pot on the O2 is only accurate to about 20% between the two channels. The pot imbalance will show up the most at low volume levels. A way to correct that is decrease the value of R21, or R23 (Whichever gain setting you are using), to bump the gain in the right channel up a bit.

For example, if your R21 is 1K right now, you have 1.5K/1K + 1 = 2.5x gain. If you drop R21 about 10% to the next standard resistor value, 910 ohms, that would bump the right channel gain up to 1.5K/0.91K + 1 = 2.65x.
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Old 7th January 2013, 08:28 PM   #3012
ericj is offline ericj  United States
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Granted. Maybe something like the guts from a slim profile cable mount jack.

But even then, you might have to solder the opamps to the board and use long leads on those two capacitors so they can be bent out of the way a bit.
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Old 7th January 2013, 09:33 PM   #3013
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Quick question: do both grounds on the ODAC need to be connected, or can I connect one only?
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Old 7th January 2013, 10:14 PM   #3014
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30 minute edit expire just passed, was going to add some photos into my previous post. I scrapped my CAT5 cable for connecting the ODAC to the O2. I just got some Van Damme Starquad Miniature microphone cable I'm going to use for a headphone recable so I cut a bit of that off and used it instead. A little bit overkill, perhaps, but it worked out well. Firmer cable, easier to solder.

As you can see, I made a bit of a dog's dinner of the ODAC soldering but I somehow got throughout without wrecking anything. I was able to coax enough solder out of the holes (but not 100%) and then force a long piece of unsheathed Van Damme through - I then bent it a little bit, soldered and then trimmed. My issue the last time was not having three pairs of hands to hold the CAT5 in place, the solder and the iron. The right channel's ground was an afterthought. I tried to get away with only using the L ground, but when I hooked everything back up I wasn't getting right channel. In my efforts to fix it, I hooked up the R ground but it turns out the issue was that the trace I cut on the O2 for the R channel had somehow got a little bit of solder in it. Fixed that up.

https://www.dropbox.com/sh/bf0c4uficuzn91u/GY1n0POL_-

Click the image to open in full size.

Click the image to open in full size.

Click the image to open in full size.
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Old 8th January 2013, 04:13 PM   #3015
ericj is offline ericj  United States
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Well I still haven't opened up my o2, but there were bits I was going to order from mouser anyway, so I ordered new regulators, fets, etc.

I'll let you all know what it turns out to be.

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Old 9th January 2013, 05:59 PM   #3016
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Quote:
Originally Posted by agdr View Post
To track down the imbalance it would help if you could disconnect the left channel wire from the ODAC on the O2 end, then jumper over the right channel connection to the left channel connection with a short jumper wire. That way you are feeding the right channel from the ODAC to both the right and left channel on the O2. Both channels then should sound exactly the same if the problem is the ODAC, otherwise the problem is with the O2.

The volume pot on the O2 is only accurate to about 20% between the two channels. The pot imbalance will show up the most at low volume levels. A way to correct that is decrease the value of R21, or R23 (Whichever gain setting you are using), to bump the gain in the right channel up a bit.

For example, if your R21 is 1K right now, you have 1.5K/1K + 1 = 2.5x gain. If you drop R21 about 10% to the next standard resistor value, 910 ohms, that would bump the right channel gain up to 1.5K/0.91K + 1 = 2.65x.
Thanks for such a helpful response. By "accurate to about 20%" do you mean there could be a 20% difference in the channels? That seems a lot. I'm not sure how the measurements work.

Could a "better" pot be hand to reduce this difference?

RE: my hearing a channel difference, it turns out that I have some sort of ear infection as a result of tooth pain. Got an appointment booked for next week, really hope it isn't permanent!

My luck to buy a fantastic amplifier and DAC and then something happens that means I can't enjoy them!
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Old 9th January 2013, 10:54 PM   #3017
agdr is offline agdr  United States
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Quote:
Originally Posted by cruncynutcornflakes View Post
By "accurate to about 20%" do you mean there could be a 20% difference in the channels?
Yep. And that is actually considered good for dual gang pots. Check out "total resistance tolerance" specification here:

RK097 Series - Basic information

Quote:
Originally Posted by cruncynutcornflakes View Post
Could a "better" pot be hand to reduce this difference?
About the only other thing is a stepped attenuator, a pricey panel-mounted gizmo about the size of a small pine cone:

High Quality Audio & Industrial Attenuators

Quote:
Originally Posted by cruncynutcornflakes View Post
it turns out that I have some sort of ear infection as a result of tooth pain.
Keep that O2 resistor modification in mind, if needed, to bump up the gain in one channel. Best of success with the ear exam!
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Old 10th January 2013, 11:24 AM   #3018
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Default recharging batteries

Do you need to power it up while it's plugged into the power adapter?
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Old 10th January 2013, 11:30 AM   #3019
swalter is offline swalter  Switzerland
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Quote:
Originally Posted by merlin2069er View Post
Do you need to power it up while it's plugged into the power adapter?
no, batteries will be charged as soon as the AC adapter is plugged in.

Stefan
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everything O2 and ODAC related can be found here: www.headnhifi.com - your DIY and audio resource
or have a peek in our vendor forum: http://www.diyaudio.com/forums/head-n-hifi-walter/
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Old 10th January 2013, 11:32 AM   #3020
swalter is offline swalter  Switzerland
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Quote:
Originally Posted by cruncynutcornflakes View Post
Quick question: do both grounds on the ODAC need to be connected, or can I connect one only?
Better late than never... If you connect only one of the ground pads from the ODAC to the O2 will be OK.

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