Monday, 20 August 2012

O2 headphone amplifier + ODAC

So, I've bought an O2 headphone amplifier diy kit from and also a pre-assembled ODAC board (don't want to DIY that one!). Everything was packaged very well, credits to Stefan at headnhifi for that.
After opening the box...  Click for a bigger picture.

All stuff that was in the package.  Click for a bigger picture.

I started with measuring all the resistors and organizing them in a good way as to not mix them up. The bottom row of resistors are the extra gain resistors supplied with this kit.
Resistors measured and organized.  Click for a bigger picture.

Then I started by mounting the resistors on the board, starting with the smallest ones and ending with the biggest ones. I've heard it's a good idea to not mount the big ones in the bottom right corner directly on to the board. It's good to keep a couple of millimeters between them and the board, probably because they will become hot during operation, I guess. I simply put a little spacer between the resistor and the board when I was soldering and then removed it when I was done.
Resistors mounted on the board.  Click for a bigger picture.
After the resistors came the small capacitors. I was a bit confused by C6 and C7 (just me being a bit dumb) so therefore they aren't mounted in this picture or the coming pictures. But they are supposed to be there and I will mount them them before finishing. I also mounted the diodes, remember to mount them in the right direction! It might be a bit easier to mount the diodes before the big ass resistors at the edge of the board. Remember "lowest components first on the board".
Diodes and small capacitors mounted, except C6 and C7.  Click for a bigger picture.
After that it was time to mount the DIP-sockets and film capacitors. Said and done...
Film capacitors and DIP-sockets mounted.  Click for a bigger picture.
After that it was time for the... I honestly have no idea what they are called but they are three-legged things and you'll see them in the picture (although slightly out of focus). Think they might be called rectifiers or transistors, not sure.
Three-legged thingys mounted on the board. One very small, two bigger ones and one really big one.  Click for a bigger picture.
Then it was time to mount some more capacitors. Started with the smaller round ones and the two tower-shaped ones. When mounting capacitors to the board like this it's very difficult to make them sit nicely to the board so I only solder one leg. Then I reheat that joint and push the capacitor flat to the board and adjust it so it's not leaning in any direction or so. This is also a good opportunity to double check that the polarity is right. Do NOT mount these the wrong way, then shit will happen :P Then I solder the second leg.
Some more capacitors mounted. Click for a bigger picture.
Time to mount the four biggest capacitors. Said and done using the technique described above.
Big capacitors mounted. Click for a bigger picture.
Now when everything (except the C6 and C7) are mounted it's time to put on the connections, switches and all that. The holes for the volume pot confused me a bit so I had to try mounting it in the case and putting on the volume knob. I found that the back set of holes worked best. Remember to get these items as straight as possible, otherwise it can be difficult to fit the front panel or the volume knob. I manage to get the LED and the volume pot pointing to the side a bit so I had to heat up all the solder joints and try to bend them straight. It worked but you should do it right from the beginning! Also, for the battery connections (only two are needed since I'll put the ODAC there) it's a good idea to use the same technique as with the capacitors, to get them as straight and flush as possible.
Connectors, volume pot and switches mounted. Click for a bigger picture.
Now when everything is kind of done I thought it would be a good idea to clean the board, I've heard that's very important to get rid of flux residues. I've been told that denatured alcohol is ok to use, we have something in Sweden called t-sprit which I've used before to clean off old thermal paste from CPU-coolers and such. I thought I had some of that at home but apparently I didn't. I found some k-sprit which is used for cleaning carburetors but it is denatured alcohol too so I soaked a bit of paper in that and wiped the board "clean". It didn't end up much cleaner than before so I think it didn't help much really, see the picture below.
The not so very clean board after using k-sprit. Click for a bigger picture.
To finish this I need several things. First I need something to clean the board with. Then after that I need two m3 bolts and nuts and some cables to mount the ODAC to the board. Then I need to mount the chips in the sockets (I thought it best to leave those in the ESD-bag for the moment).

I have also cut the ground traces as described on NwAvGuy's blog for mounting the ODAC to the board. I just took a sharp kitchen knife and careful cut the traces. Measured before with a multimeter and had close to 0 ohms and after cutting the traces it was not the same result so apparently I've succeeded in cutting them.


  1. I bought the same kit as you and me to I am comfused about C6,C7. The capacitors included are ceramic instead of film and they measure 1.05uF instead of 2.2 as the diagram calls for. What did you do?

    1. If you look at this picture

      You can see the I've mounted the C6 and C7. I don't remember exactly since it was a while ago I built this but I think they were the same values actually and they work well as it is now.

      If you still aren't sure you could ask in this thread

  2. Thanks for the blog post, I too was confused about C6 and C7.