O2 headphone amplifier + ODAC

So, I've bought an O2 headphone amplifier diy kit from www.headnhifi.com 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.

Vinyl vs CD

CD version. Click for a bigger picture

Vinyl version. Click for a bigger picture

So, basically what you see here is the same songs. It's the movie soundtrack to Inception by Hans Zimmer. Very very good soundtrack and it's my favorite one. Very good audio quality and very good music, extremely well done all of it and I can strongly recommend it.

Back to the topic. The upper picture is a MasVis analysis of the CD version. As you can see it still has pretty good dynamic range but brickwall limiting exists at a couple of places, unfortunately. The lower picture is the same kind of analysis of the vinyl version. Here you see far better dynamic range and zero brickwall limiting. The only downside with the vinyl rip is the crackling and static noise that typically occurs on vinyl.

Another example of this is the album Scary Monsters And Nice Sprites (2010) by Skrillex. Unfortunately I don't have both versions available at the moment but I remember seeing lots of brickwall limiting on the CD version while the vinyl version had none of it and sounded clearly better, even though it had some static noise and crackling as per usual.

41Hz AMP15-PS XP UPDATE #3

So I've continued my work with the amplifier and soldered tha cables and jumpers to place. But I also got to know that I've mounted the diodes the wrong way around. The anodes should be towards the FET and I've mounted the cathode towards the FET. So this means I will have to remove two of the cables, all four diodes and one resistor and then turn the diodes with the very short legs and then put everything back in place again. I'm a bit disappointed at that, not very clear assembly instructions to be honest.

But after I've done that I should be ready to go, just clean the board with something (I heard denatured alcohol would be okay), put some heatsinks on the transistors for the pre-regulators. Also remove all the screws and bolts from the TO220 devices as apparently the heat slugs carry voltage. Will have to use some glue or something to hold the nylon washers in place.

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Diodes correctly mounted with the anode towards the FET. Click for a bigger picture.

41Hz AMP15-PS XP UPDATE #2

My first post about this amplifier can be found --here--

So I'm pretty much finished with this amplifier now. Both toroid inductors are done and soldered into place (this was a hell of a job!). Soldered the four remaining small capacitors and then the massive bulk capacitors. Damn they're heavy!

What remains now is to find out how to place the jumpers, put some wires on the back of the board (I don't know why but I've seen on pictures that there are a couple of wires on the back). And when all this is done I'll have to test it to make sure everything is OK and then I'll mount the IC and hook it up to some speakers and see what it can do.

Before the bulk capacitors. Click for a bigger picture.

Everything mounted (except the IC). Click for a bigger picture.

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41Hz AMP15-PS XP UPDATE #1

My first post about this amplifier can be found --here--.

So, I've found out how to properly solder the surface mounted resistors on the back and finished soldering them. I've also found out how to identify the different diodes. There were one 10V diode and one 13V and they looked exactly the same. I was told at diyaudio that there should be numbers written on them so I took a magnifying glass and managed to find the part numbers and googled it. Soldered them to place on the backside in parallell with some resistors. Very hard work getting it right and avoiding shorts.

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I've also soldered some more capacitors and a transistor.

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As you can see in the picture I've winded one of the ferrite core inductors but I am unsure if I have done it properly or not, so I'm waiting for somebody to judge my work before I solder it to the board.