DIY Sennheiser HD650 cable build

I’ve read too many posts, here and on other forums, about the Sennheiser HD650 stock cable being less than it should be. So I decided to build my own. (Sorry, no pictures – maybe next time!)

I bought Cardas HPSC and GRQ SS connectors. The HPSC are the can connectors and the GRQ SS is the ¼” plug. I don’t normally plug the vendors I buy from unless they do something special but I bought these from Dedicated Audio LLC out of Arizona. No hassle, good communication. I ordered two of each of these and they were drop shipped from Cardas. There was some miscommunication and I only got one set of the HPSC’s. Within 30 minutes of emailing Dedicated Audio on a Friday evening I had a reply and shortly after an assurance that Cardas was drop shipping another set to me. I also bought 15 feet of ¼” tech flex. For wire I used 10 feet of Mogami Neglex 2534 which I’ve used for interconnects in the past. Some ¼” and 3/8” heat shrink from my stock to finish things off with. About $75 in parts. You will need an ohm meter if you use this wire – it’s only two colors for four wires.

My headphone amp is a Bottlehead Crack with the Speedball upgrade. I also upgraded many of the internal components as I built it. If you’re curious head over to Bottlehead and in the Gallery forum - a couple pages in now – you’ll find my Crack on Speed with Blueballs. I’m using an Amperex 7316 tube in the 12AU7 spot and a heavy duty Raytheon 6080WC in the other socket. I really didn’t have any issues with the sound of the HD650’s but I needed to hear for myself.

I started on the ¼ plug side and my first confusion was that the plug has no connection for the right side positive – it’s just a barrel! If you’ve not worked with the Cardas line you’ll also find that what they provide to solder the ground to can be tricky if you don’t keep things smooth. I usually dent the inner ring and solder into the dent. This time I got over zealous and broke the ring – it actually worked out better as I could pull the ground wires into the gap to solder. I used about ½ of the shield wire and the two blue wires for ground. Measure out the left and right positive so that the right will have insulation on it as it goes over the left. Solder in the left (center) first. For the right side I just spread the fine wires from the Mogami over the barrel and soldered it down. Because the Cardas and Mogami are good quality it took and was easy to do. You MUST insure this is not a cold joint. Tug on it a bit to see if it holds – I just hook a small screwdriver under the wire and pull up slightly. I then combined the shield wire and the two blue conductors and soldered them into the gap I made. I put two layers of 1/4” heat shrink up into the plug as far as I could – one at a time. Then I worked the tech flex slightly over the connector – then worked the barrel over this and screwed it down. The tech flex is now inside the barrel. I dinged the tech flex a bit working the outside of the barrel over that last inch or so where the heat shrink had built up over the Mogami so I pulled about 6” of 3/8” heat shrink right up to the barrel and heated it down. Once you have all this done there is no going back into the barrel without messing up a great deal of heat shrink and tech flex – so make sure all is well before you begin to pull and heat.

Notice I didn’t keep track of which signal wire went where – I’ll ohm that out when I get to the other ends.

I cut the tech flex back about 12 inches from the end of where the Mogami ended. My stock cables have about 9” of “hang”. I heated a small piece of heat shrink over this end of tech flex to keep it in place. I removed the outside insulation and all of the shield up to this point in the wire and untwisted the two pairs. Mogami wire has a center piece of plastic that you’ll need to cut off as well. Get out the ohm meter. The tip of the plug is the left channel, the center is right and the base is ground. Because both blue wires are ground it won’t matter which of these you mate to the white wires. Once I determined which wire went where I used a small piece of heat shrink to “mark” each side – red to right, black to left. I kept the twists intact for each pair and put enough heat shrink on these pairs to leave about 1” at the connector end. Red on right, black on left. I put tech flex on these two pairs next (the red heat shrink is now just barely visible). In order to pull ¼ inch heat shrink over this (to secure the base) tape the ends at the connector down tightly and the heat shrink will go right over without messing up the tech flex. I finished the junction with some 3/8” heat shrink – a couple of layers to pull it all together. I would not strip less than 12” of wire back – by the time you’ve got this split looking good you’ll have lost an inch or two due to heat shrink. Now I carefully pulled the tape off of the other end and put some heat shrink here to hold down the tech flex. I used my red/black combo again but it’s not necessary because you can see the red heat shrink through the tech flex.
The HPSC connectors do NOT have any cover over the connectors, the plastic is decent but not something you can stand your soldering iron on for a long time. You’ve got to measure carefully. The small pin is the signal pin (white wire), the large pin is ground (blue wire). I had to take one of my ends apart after the work was done because I had a cold joint that broke free – that’s no fun - so take your time and insure those pins are done correctly. I used two layers of 3/8” heat shrink to cover the open area after my soldering was done. You can slip this over the connectors if you forget to put it over the wire before soldering. There is a ridge on the HPSC connectors – you can heat shrink just slightly over this but not too far as it will not connect to the headphones correctly – another learning experience!

Issues – Mogami wire is very flexible but the tech flex stiffens it up – and I’m not loving it. The tech flex can also be “heard” if you move around. Hard to describe – but if you run your fingers up something with ridges you’ll hear it – if it’s smooth you probably won’t. I won’t put tech flex on the next version. It does look nice and clean but…
The ¼ Cardas is nice but I don’t like how it finished. You can’t get 1” heat shrink over it so I’ll get something larger in a 3:1 shrink and see if I can get more of a strain relief on it.

The sound (why this was done in the first place)… OMG!! These aren’t broken in by any means and the bass is over the top. Separation of voice/instruments seems much better. It’s a cleaner sound by far over stock. I’m not going to rave on until they’ve got more time on them but I doubt that the stock cables will ever be used again!

Was it worth $75 and a couple of hours? Absolutely.