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!)

Click for a bigger picture.

Click for a bigger picture.

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