Polk Cobra De-enamelling and termination

Polk Cobra de-enameling and termination

Here is a short write-up on experience de-enameling and termination Polk Cobra cables. Please note again that the enamel is TOXIC. Mr Arthur Salvatore published an earlier version on his website.

Working with Polk Audio Cobra Cables: A novice’s journey

My experiences with these cables: what works and what did not.

Remember: The individual strands of these cables look thick with their insulation on. Once you remove insulation, you will be surprised to note that the copper strands are really thin (like fine wire). If you have not done so, please read Mr Arthur Salvatore’s column before you go on.

Method 1:  Mechanical scraping of the insulation.

Yes it works but it is very time consuming. I found that the best method was to pull a few strands at a time between two sheets of fine-grain sand paper. You have to keep turning the cables around so that all the enamel is scraped off by the sand paper. Very time consuming because of the large number of strands.

Mechanical methods that are not that effective are listed below.

·         Scraping with metal file. The fine strands tend to break off.

·         Using a sander/grinder. Even careful application of pressure and selection of soft grinding surfaces causes some cables to break off.

·         Metal scraping tool. No good. Too many strands break off.

After removal of enamel, it is important to solder the exposed copper immediately. Please do remember that we are working with 30 year old copper wire. It is still usable due to the purity of the copper and the excellent protection of the enamel. Avoid exposure, as much as you can.

Method 2: Burning off the enamel with fire (lighter)

Not workable in real life.

·         The intense heat of the enamel burning burns off the copper wire. Please note that the enamel thickness is much higher than the cable diameter. You end up with different lengths of burned up cable ends.

·         To make it worse, the copper gets oxidized by the fire/heat.

Method 3: Chemical stripping

Theoretically this is a good technique, but quite difficult in real life.

·         The tight Litz braiding and the close fitting plastic sleeve has a tendency to absorb the solvent from the stripping chemical by capillary action. I found that even holding the cable vertically and dipping it into the stripping solution from above does not prevent capillary action. I destroyed 1 m of my cable trying this method.

·         The copper quality (purity) may be compromised by the stripping solution.

Method 4: High Temperature Solder pot

Best of the four methods I have tried.

1.    Use a high temperature solder pot (temperature about 400^oC)

2.    Melt enough solder to be able to dip (about 1.5 cm deep) the required length of cable.

3.    Wait till temperature reaches 380^oC-420^oC.

4.    Dip the cut end of the cable in the melted solder and wait till the enamel burns off. You can see the white fumes (and nasty smell if you do not wear PPE), indicating the enamel is burned off. Takes only a 10-20 seconds if the solder is hot enough. Slowly move the cable back and forth so that all strands are de-enamelled.

·         Separate the strands by color twist them together lightly. This will make dipping them in solder easier. Ensure no mixed strands (a single mixed strand out of 144 will short your cable)

·         This white gas is toxic. Wear a chemical grade mask (dust mask such as N95 is not good enough). Do this is a well-ventilated area

·         Use a long plier or similar to hold the cable. Does not hold the wire with bare hands as you burn off the enamel. It can become very hot.

·         Protect the rest of the wire from the extreme heat by wrapping the cable (just above the section to be dipped) with a thick layer of aluminium foil to conduct away the heat. Or use holders with heat sink.

·         If it takes too long, the solder pot is not hot enough. If the solder is too hot, the copper wire will melt. If you are doing this the first time, cut off a couple of strands and test.

5.    If necessary, apply solder paste and dip in solder momentarily.

6.    If you plan to terminate using connectors, prepare them ahead and assemble them straight out of the solder pot.

Good luck and happy listening.

To all the brave souls who would to attempt this: these cables are really worth investment in money and time.

Note: Arthur Salvatore noted that the enamel can also be burned off using a high-temperature soldering iron. The results are not pretty due to large number of strands but it works too. I have not tried this method but others have done this successfully. After you burned off the enamel, bunch the cables together and solder the ends.

Note: I will add more photos later.

Preparation for Polk Cobra termination

Chemical grade mask and goggles are COMPULSORY!