O2 headphone amplifier + ODAC update #5 (cables switched and gain resistors removed)

As the title says, I have switched the cables between the ODAC and O2 and removed the gain resistors R17 and R21.

Switching the cables may sound very easy, and I had expected it to take no more than a couple of minutes to do. I was wrong. Very wrong... It took me about 40 minutes in total because removing the wires was hard and then getting them back on was even harder. The holes had been messed up so I had to surface mount the cables on the back of the ODAC with a lot of solder to keep them in place...

Removing the gain resistors was easier though. It was pretty narrow but I could fit a tweezer between the resistor and the board. Then I heated up the joints on the back while pulling with the tweezer and eventually the joints let go of the resistor and it flew away through my room :P Now the gain is on a better level, no noise at all, even with the volume knob turned all the way up and there should be less distortion, especially in the higher frequencies.

Now when I have proper stereo sound everything sounds incredibly good and even if this amplifier costed 4000SEK (that's about $600/€480) it's still a very good buy.

I'm planning to sell this one though. Make some profit to buy myself a proper DMM and some soldering equipment. Remember I have only borrowed the soldering stuff from a friend, for a couple of months now. Should buy him some gift too for the profit I make. Then I'll build two-three more and keep one for myself and sell the rest. I'll be selling an Asus Xonar STX soundcard soon too, because as far as I can hear the O2+ODAC beats the STX.

Do I sound happy and satisfied? Yes, of course I am!

O2 headphone amplifier + ODAC update #4 (mono signal)

So, now I have found out why it sounds so much different and "boring" with the O2. It's because it's mono!
I've had my suspicions when soldering the cables between ODAC and O2 but I thought I'd better follow the guide... It turns out that in the guide the author had reversed the white and black cables which means that I have done it totally wrong and will have to open it up and reverse my cables. I have of course told Stefan Walter and Headnhifi about this and hopefully he will correct it.

I will fix this tomorrow and take some pictures of the process. Hopefully I'll end up with a kickass DAC+amplifier when I'm done :)

O2 headphone amplifier + ODAC update #3 (Up and running!)

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So, today I finished this project. To find some M3 nuts and bolts I first went to a local store selling such things. They did have M3 bolts but they were 25mm long and I needed 10mm. Also they had no nuts but they told me I could go to a car workshop not too far away. There they provided me with three M3 nuts, bolts and washers (only needed one bolt, one washer and two nuts though). These bolts were also too long, about 35mm or so I think. Dry-mounted the ODAC on the board as it was suppposed to be. Took a red marker pen and marked the bolt and then cut it to the right length.

I knew I had some CAT5 wire somewhere, I had tried it for speaker cables a year ago or so. Started searching and found them pretty quickly. They're perfectly suitable for this application. I cut them into proper length and when I was searching for the cables I also found another cable suitable for the ground wire, more about that later.

So here's a picture of the ODAC mounted to the board with all wires soldered.

ODAC mounted to the O2 board. All wires soldered and tucked in between the boards. Do NOT use a thick stiff cable for this. Click for a bigger picture.

 I did the switched version, more about that can be found in this PDF. It was pretty simple and straight forward, a very good guide I must say.

How the board is put into the case. Click for a bigger picture.

I have read on the internet that it's a good idea to scrape some paint off the inside of the case somewhere and then put a cable from the front center pin of the 3.5mm input to the case. This for some kind of ground making the amp slightly quieter. This was easily done by using the wire I found, a 1.5sqcm cable I think. Soldered one end to the pin. I then peeled off the insulation of the other end, realising that I had to take away some of the strands to be able to do as I had planned. I cut off maybe 2/3 of the strands, then spread them out a little like a fan. I scraped some paint off just by using a flat screwdriver. The paint goes off easily. Then put the strands at the surface where the paint is scraped off, then put the back plate on, hold it tight while screwing it to place clamping the strands between the back of the case and then back panel.

This is how the scraped surface looks like.

I seem to be unable to rotate this picture, so I'll leave it like this... Well here you can see the green ground wire running under the board to the back of the case where it's clamped between the backplate and the case.

O2 headphone amplifier + ODAC update #2

I borrowed a better DMM today (Thanks to Pelle Nilsson) and measured the voltages with that and everything was fine and as it should be. Mounted the remaining chips in their sockets and right now the board is mounted in the case (sorry, no picture yet). Tomorrow I will try to figure out a good way to connect the ground wire to the chassis and then try the amp for the first time. I wont be using my Denon headphones though, because if there's something wrong I don't want to damage my expensive gear. Instead I will use a pair of old Steelseries Siberia V1 headphones, I don't care if they blow up since they'll never be used again anyways. Hopefully everything will be all right.

I will also continue my search of two M3 bolts and nuts so I can mount the ODAC to the board. And before finishing it all I will need to put some kind of spacer between the board and either the back or the front of case. There is maybe 1mm clearance so the board is going back and forth which is a bit annoying.

O2 headphone amplifier + ODAC update #1

I have now mounted C6 and C7 to the board. After that I read the initial testing guide over at http://nwavguy.blogspot.se/2011/08/o2-details.html#initialdiytesting

Checked the power supply voltages with success (I think). According to the article the DMM should read 23-24V while mine showed 25V. Nothing got warm or hot as far as I could feel. Turned the power off and installed U2 and repeated the test above with the same results as should be. Then I moved on to the second test and this is where I hit some problems. I measured from the negative battery terminal of BT1 to pin #4 of the empty U4 socket and it should be close to -11.8V but my DMM showed -0.00V. Switching the probes gave me 25V reading. I then measured from the same negative BT1 to pin #8 of the same socket and this should give 11.8V but I got 25V again.

So right now I'm waiting for help, hoping that somebody will answer me in the O2 thread at diyaudio.com

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.