Sennheiser Headphone renovation for next to nothing...

I've just finished renovating a vintage pair of Sennheiser HD420 headphones that I've owned for over forty years. The renovation was cheap; it was simple and took no more than half an hour to complete.
But why waste time on a forty year old piece of electronics? Surely modern headphones are much better and only a click of a mouse away? Well, maybe, but I love the sound of these old phones and they are so light on my head I can wear them for hours - even with glasses.
I bought my Sennheiser HD420's when they first came out in the late seventies. Since then, they've been my choice in headphones over any newer headphones I have bought or listened to. They are one of the most openly transparent, detailed headphones I have ever listened to - if perhaps a touch light at the bottom end. They do benefit from being driven from a higher voltage source such as a hi-fi amp rather than straight from an iPod or MP3 player but they still sound good on portable devices.
So what was wrong with them? The foam earpads had perished and had literally gone to pieces inside the cloth covers and the headphones were becoming uncomfortable to wear. I tried looking on Sennheiser's web site - and their support site - for replacement pads, but it appears that you cannot get hold of them any more. Such a pity.

There are other HD420 owners on the Internet also seeking replacement earpads so I thought I'd see what else I could do - and hope that my findings are of use to others.

The Sennheiser HD420 earpieces come in three parts. There's the transducer in its plastic housing, an acoustic foam insert and a cloth cover that holds the foam to the transducer. As long as the cloth cover is intact and the headphones work, then all you have to do is replace the pads.
  1. First measure the earpiece diameter (they are 80mm)
  2. Next search Amazon for "80mm replacement earpads"
  3. Buy one of the items that come up in the results
That's the easy bit.

When they arrive you have to replace them. This needs patience, fingers, kitchen paper and an old toothbrush. No other tools or you risk damaging the cloth cover or the headphones.
First you must tease off the cloth covers. Use your thumbnail and carefully ease the plastic surround all round before gently sliding the surround off the transducer.
When the cloth cover is off, clean as much of the old ear pad from the cloth as you can (in the picture all that orange crud is the old earpad).
Now, with a toothbrush (and nothing else!) gently brush all the compressed and rotten old earpad from the transducer. Be careful - the white in the transducer is material and this can easily be damaged if you use too much force. Remember it is forty years old!!

Here you see the new earpad with one of the cloth covers
Here you see the new earpad in position over the transducer
To re-fit the new pad and the cloth cover, first tuck the pad into the cover as seen here.
You now need to gently get the cover back on the transducer. I did this by holding the plastic surround in place with one finger while I gently eased the surround back into place around the transducer. The hardest part is the last inch so make sure that the last inch is away from the wire and the headband so you have the most control. Don't use tools or too much force or you'll tear the cover. Of course you can take the transducer off the headband (it just pulls off, but remember it is old so it could be brittle) and you can also pull out the wire, if this makes it easier. I decide not to do this and did not have any real issues, but the choice is yours.

Finally the restored Sennheisers, all padded out and once again, fit and ready to listen to.

Total cost?  less than £3.00 and under thirty minutes. Satisfaction?  Priceless.  :)