Wednesday, 3 February 2016

Update on the new Porta Pro cable

A while ago I changed the cable on my Koss Porta Pro to a new one bought off ebay. You can read about this in my previous blog post. It seemed like a reasonable cable although not the sturdiest. However, considering the original cable lasted me around two-three years I was hoping to get at least a year of use out of this new one. That turned out to be wrong. Today I was going to go for a walk and as the great music fan I am I wanted some music in my ears while walking. To my disappointment I heard only music from the right speaker. The left side was completely dead. I tried replugging the cable to my phone, no difference. I thought maybe there is something wrong with the phone so I tried connecting them to my O2+ODAC combo, but the problem remained. I examined the cable for any visible damage and I couldn't see any. I tried jiggling around the cable along its whole length to see if I can get a connection somehow. No success. I took of the speaker from the frame and opened it up to see if the solder joints were still intact and they were. Apparently the cable must have broken somewhere and I can't find it.

Right now I don't know what to do. A new cable would cost me around 40SEK and a month of waiting and may only last another month or two. A new pair of headphones would cost me 300SEK and would hopefully last at least a year or two. I could try with another, sturdier, cable, such as a normal 3.5mm to 2xRCA but that would probably cost ~80SEK and would require some modifications to the headphones which might not turn out very well. I really like the Porta Pro headphones because in my opinion they are the simply the most portable non-in-ear headphones and they do actually have a decent sound for its price level.

Friday, 11 December 2015

Koss Porta Pro cable replacement guide

My second pair of headphones, the Koss Porta Pro, has served me well the last couple of years and I am surprised at how well they have withstood all the abuse they have been put through. I used them when I was sanding the Oy cabinets. I had them with me on my trip around the world, carelessly packed in my backpack or pockets. They have been with me on over a hundred workout in the gym and then afterwards just tucked in my gym bag along with other items. The frame is still perfectly straight. The foam earpads are looking pretty ok, just a few holes on the edges. The cable has been the part that has handled the abuse the worst. About half a year ago it turned really stiff so it wasn't a very good idea to fold the headphones and then wrap the cable around them. I did that anyways though and eventually the outer insulation snapped in half and it was only being held together by the really thin wires. I solved this temporarily by using some electrical tape. It didn't last very well though and I had to change the tape every two weeks or so. I ordered a 3.5mm -> 2xRCA cable that I was planning to use as a replacement. However, that cable got put in use elsewhere (between the O2+ODAC and my stereo amplifier) so I kept on using the electrical tape. Last week when I was about to go for a walk the sound just died in one side. One of the wires had broken. I managed to fix this with some soldering and lots of electrical tape, a really ugly short term solution. Meanwhile I had ordered a replacement cable from Ebay.

Short term electrical tape solution.
The replacement cable arrived today and I just couldn't wait with replacing the old cable. I found this guide over at iFixit which shows how to disassemble the headphones but also how to do if you have a non-standard replacement cable, similar to what I was planning to do in the beginning.

I decided to write my own guide for you, based on if you have the same cable as I have. I bought this cable from tuttoit on ebay. It is cheap, shipping included and it looks ok. I have no idea about the durability yet but I will come back later to comment on that. As usual it took quite a while for it to arrive but that can be expected when ordering things from Asia with free shipping.

As the iFixit guide mentioned above says you need to start by removing the speakers from the frame. You do this by gently pulling them apart. With a bit of force they will snap off from the frame.

Then you should remove the black foam. It just hangs onto small plastic pins running around the edge on the backside. Gently lift it off the pins and remove it.

Now is also a good time to make sure there is no dirt or hair behind the black cover. That could potentially degrade the sound. If you have had the headphones for a while there will probably be some stuff there. Gently remove it and be careful not to touch the speaker drivers.

The next step is to remove the plastic cover covering the wire. For this you need something pointy, like a flat head screwdriver, knife or similar. Bend gently and it will start coming off.

Take note of how the cables are soldered. Take a picture with your phone or write it down on a piece of paper.

Begin with desoldering the wires to one speaker. Don't do both at the same time. I would recommend trying to be as quick as possible when heating up the joint and removing the cable. The plastic can deform or even melt if you keep the heat on for too long.

New cable soldered to the connector.
As you can see in the picture above I kept the heat for a little too long so the plastic deformed a bit around the hole where the pin on the cover goes. This turned out to be a little problematic since the cover didn't want to come back on again. I had to scrape some plastic out from the hole to make it a little bit bigger.

The last step is to wrap the cable around the pins. This way it is protected in case you would pull on the cable. Put the cover back on and then put the foam pads back on. By this time you have probably forgotten which is right and which is left, but don't worry. It doesn't really matter, just run some stereo channel test track and you can easily figure it out. I used this track on YouTube. Then just push the speakers back in place on the frame you are done.

Hopefully this will allow me to use these fantastic headphones for another year or two. Sure, they are no hifi headphones but considering how cheap and portable they are amazing. Perfect for when you are out taking a walk, running, or training in the gym. Heck, I actually think they sound better than most other headphones that I have listened to it the same price range.

Estimated time: 10 minutes
Estimated cost: ~40SEK / ~$4.5 / ~€4 / ~£3
Difficulty: Basic
Tools needed: Soldering iron, flat head screwdriver or other pointy object

Thursday, 22 October 2015

Experimenting with a quieter power source for the MiniDSP

As exams are approaching I find myself spending more and more time by my desk with faint background music on as I study. As I lean forward over my books my head comes within 40-50cm from the speaker drivers so any noise will be very audible.

I have been running the MiniDSP hooked up to my system even though I am not using any subwoofers at the moment. This is because the mid bass becomes a bit overpowering in my room as soon as I turn up the volume a bit. I have been using a small wall wart as a power supply for my MiniDSP 2x4 for years now but the noise haven't bothered me at all since I haven't been listening near-field. If I sit a couple of meters away from the speakers I can't hear any noise at all.

I did some googling on the problem and found a thread where some guy suggested powering it with a 9v battery to see if it was the wall wart that was introducing the noise, because apparently batteries are supposed to be a quiet (but not very convenient) power source.

By chance, I happen to have some 9v batteries lying around from my previous O2+ODAC builds.

The sacrifical cable to the left, a 2.5mm male to 2x2.5mm female cable.
I also had a spare cable which I ordered just a couple of weeks ago. The plan was to use it as a replacement cable for my Koss Porta Pro headphones, but I realised I should get something sturdier (which I have, just waiting for my heat shrink to arrive from China).

I started by cutting off the useless 2.5mm female connectors. I mean, have you ever used one of those? Well, I haven't.
Shielding/ground and signal wire.
Apparently the cable had a shielding/ground wire and a signal wire, which makes sense after all. I decided to use the outer ground wire since it was thicker and I didn't have to peel an extra piece of insulation.

The next problem was how to connect the wire to the battery, without holding it in place with my hands. One of the connectors on the battery allows for winding the cable around it but the other one does not. But as it happens to be, batteries are not the only things I get left after building an O2+ODAC combo. I get spare battery connectors as well. Might as well sacrifice two of them for this experiment.
Wire soldered to a battery connector.
This way I can attatch the cables to the battery without holding them in place. However, another problem appeared. These connectors are meant to be soldered in place on a circuit board, fixing them in place so they can't rotate and touch eachother which creates a short circuit. My solution to this was electrical insulation tape.
Tape-wrapped and insulated battery connectors.
I used my trusty soldering iron to melt the tape in a few places to fuse it together so it wouldn't fall apart as easily.
Finished "product".
After finishing the battery connectors I simply connected the other ends of the cables to the MiniDSP. No fire, no smoke, no weird sounds. All good. Next step - connecting it to the amplifier. No fire, no smoke, no weird sounds. All good so far. Turn on the amplifier and wait for the "click" that turns on the sound. Dead silent, no background noise. Wow, did this really work? I turn on some music but the speakers are still dead silent. I unplug the battery and plug in the USB cable. Background noise appears again along with the music.

My first thought was regarding the age of the battery. I think the battery I tried was from my own O2+ODAC build several years ago. I take it these batteries are not high-end and maybe they lose charge by time? I fetched my DMM to check the voltage.
3.91 volts, the MiniDSP 2x4 requires at least 4.5 VDC.
Turns out I was right, the battery had lost too much charge. But as it happens to be, I had seen some other batteries in my box full of newer O2+ODAC supplies while I was getting all my tools which where in the same box. I fetch the newer batteries and measure them. The first one measured around 7.5 VDC and the other measured 8.83 VDC as you can see in the picture below.
8.83 VDC, the MiniDSP 2x4 can handle up to 24 VDC.
I connect the new battery to the MiniDSP, I connect the DSP to the amplifier again and as I turn on the amplifier and hear the "click" I can instantly hear the background noise again. I put on some music to see if it actually works with a battery and it did work, however not any better than the wall wart.

I am a bit disappointed with the results, I was really hoping to get rid of the noise with a quieter power supply. I guess it must be the MiniDSP itself making the noise and I will have to delve deeper to try to find a solution to this, because otherwise I wont be able to use the MiniDSP in my current setup.

Friday, 17 April 2015

The components for ten O2+ODAC combos have arrived

Earlier this week I went to pick up the package containing everything I need for the ten O2+ODAC headphone amplifier combos that I am going to build. It was heavier than I thought it would be but then I remember that the power adapters and the cases do have a bit of weight to them after all.

I have been incredibly busy this whole so I haven't had time to do anything else but open the package making sure everything was there, which it of course was.

Cases, panels and knobs in the bottom right. Power adapters in the bottom left. Component bags in the top. PCBs in the middle and USB-cables to the left and ODAC boards to the right.
Today I had a bit of spare time so I decided to start marking the resistors. Previously I have only been building the amplifiers one by one and so I have had to measure the resistors every single time which of course takes a lot of time. I estimate that it takes maybe 15 minutes to properly mark all the resistors in one bag of components. I have ten now. So I figured that if I mark one bag properly I can use it for reference when doing the other nine bags and so I should be able to save a lot of time. This way each bag took about four minutes so I guess I saved over one and a half hours of work.

Since there were no bits of paper on the two single resistors I had to make custom "flags" for them. A bit of tape and a small piece of paper worked just fine for labelling them. 

I am not sure when I will start building these because so far I haven't had time to do any advertising and I haven't gotten any requests yet either. This was thought to be a summer job but the earlier I can start advertising and selling the better it is. Selling ten of these in Sweden is likely going to take a while.

If you are interested in buying, send me a message at

Monday, 23 March 2015

Will be ready to sell O2+ODAC combos in Sweden within a week or two

I have good news for my Swedish readers. I just placed an order on ten O2+ODAC kits and I'm hoping I will get them by the beginning of next week and I'm hoping to build at least one or two before going on holiday over easter. If you want to buy just an O2 and not the ODAC, let me know and I'll make special arrangements for that.

My plan is to sell a finished O2+ODAC for ~2000SEK+shipping. I will offer custom gain settings for no extra cost. Unfortunately I will not offer any other extras such as 6.3mm output, back panel power or other colors than black (which seems to be the most popular).

Finished black O2+ODAC
So, what do you get when ordering an O2+ODAC combo from me? You get a fully assembled, fully functional amplifier and DAC. You get a 90cm gold plated (looks fancy) USB-cable. Underneath the case there will be small rubber feet to prevent scratches and stop the case from sliding around on your desk. The volume knob will be black brushed aluminium for a nice quality feel. The power adapter is a very compact one with a cord that is long enough for most people. I estimate it is around 1.5m. On request I will add gain resistors which can be useful if you want to switch gain settings in the future. I will make it so that no soldering will be required to change gain resistors, just pluck them out of the socket with a tweezers and put in the new ones. Standard gain will be 2.5x/6.5x. I haven't actually had any headphones that have needed more than 1x but for an example the Sennheiser HD600 needs a high gain. My Denon AH-D2000 and my Koss Porta Pro are just fine with 1x. 

If you are interested in buying one from me, contact me at

If you are not in Sweden but you still think that this looks like a kickass amplifier combo, then check out this site and buy your own DIY-kit.