Saturday, 20 July 2013

Objective2 headphone amplifier construction guide

Buy your own O2-kit here

Start with measuring all the resistors and labeling them.
Smallest parts first, so solder all the small resistors like this.
Add the diodes, make sure to solder them in the right direction!!! Solder the medium size resistors now too.
The IC-sockets have such short legs to it's a good idea to add them early.
Add the two big resistors at the bottom of the board. Keep 2-3mm distance between the resistors and the board since they can get warm during operation.
Add some of the small capacitors.
Add the slightly bigger capacitors on the bottom right of the board.
Add the blue capacitors.
Solder the LED first, it's important that you get it close to the board and pointing straight forward. Next att the 3.5mm sockets, they snap in to place so they are easy to solder.
Add the power socket. Solder one leg first, reheat the joint and push it in place and then solder the remaining legs.
Add the switches. This can be a bit tricky. Solder only one leg first. Reheat the joint and push the switch into place and make sure it is close to the board and pointing straight forward. If not you will get trouble with the front panel. Solder the rest of the joints when you feel satisfied with the positioning. Add the white square capacitors.
Add the volume potentiometer, try it in the case with front panel on to make sure you put it in the right position.
Volume control soldered to the board. For this kit I had to use the two row in the front.
Now add the two round brown capacitors.
As you can see in the picture there is a bridge between them. Solder the outer legs first, push them in place and then solder the bridge between them. You will need quite a bit of solder here. If you look closely you can see that the on/off switch has only been soldered as one place so far.
Add the four big capacitors. Solder one leg first, push them in place and solder the rest.
Solder the battery connectors. If you are going to mount an ODAC on the board you should only solder the two connectors to the left. If you're not planning on using an ODAC, solder both pairs. Make sure they stand straight! Solder one leg first, push to place and solder the rest.
With battery connectors on board. I will be mounting an ODAC to the board so I only soldered the left pair.
Add the ESD-sensitive parts. Be careful with these and try to avoid touching the legs. Solder smallest first and finish with the biggest. The two big ones to the left must be close to the board, otherwise they will hit the roof of the case.
Reheat ALL joints on the board. This is because when you cut the legs off components the joints may crack and provide bad connection. Reheat all joints and the solder will flow out nice and smooth. Measure all resistances and voltages according to NwAvGuy's guide on his blog. If everything measures as it should, try with a pair of scrappy headphones. Don't forget to add the opamps, and make sure you put them in the right places and in the right directions! This is very very important and triple check this before starting it up for the first time.
Don't use your expensive headphones the first time you are playing it. If something is wrong, you don't want to kill your $300 headphones. 


  1. Hi Niklas,

    Thanks for the post, helped me build my O2. I am now looking to build my second, this time with an ODAC built-in. My question is whether the battery powered O2 would have space for the ODAC board? If I read your post correctly that seems possible, anyway please let me know.Cheers.

    1. Hello there!

      It is not possible to have both batteries AND and ODAC board. The ODAC board is located where the batteries normally are. So you have to chose between batteries or ODAC.

  2. Thank you, thought the same..somehow I got the impression from your post that it was possible.