Sunday, 17 March 2013

Prolonging life [Currys by Koss HP7022 headphones]

Back in the Dark Ages (1970s) I was looking for a set of hi-fi headphones and was shown these, badged from Currys but made by Koss - I was a bit sceptical because I had never seen open-backed over-the-ear phones with only a sponge ring as a cushion, but they delivered good solid bass and were really comfortable. I don't recall the price but at the time it was quite a bit for my limited budget. In fact since then I've come to realise that maybe the bass is a bit heavy, but it isn't boomy and resonant like some, so I like the sound.



They have a 1/4" stereo jack plug on a self-coiled cable which gradually lost its spring. It still just about self-coils but can't support its own weight any more, so it dribbles down from the hi-fi onto the floor and back up to my ear. There is a simple barely-padded headband and the transducers are circular and very plain. The cushions were simple rings of foam plastic and didn't do any acoustic sealing (as befits an open transducer), and when one transducer failed many years ago the replacement from Koss had no padding and I had to transfer the foam over, which was annoying as it was glued on. There is no overall shell, just the sealed transducer with a foam ring stuck to the front and a plastic cover on the back to mount it and cover the wire terminals. The headband adjustment is done by the transducers being gimballed on a serrated aluminium strip which slides through a gap in a plastic block. Somewhere in the block there is a detent of some sort, metal or plastic, which rubs the serrations and jams the strip wherever you leave it. Actually, they aren't much different in style than ex-GPO telephone receivers from WW2. Over the years the play between the strip and the detent grew until I could put the headband over my skull and the transducers would each drop with a clunk down to their lowest position. And then, eventually, the foam started to decompose and turn to dust until I had to simply strip it off. But they still sounded so good that I wore them anyway, which is pretty uncomfortable because the transducers have a domed front which pokes your lughole painfully.

Recently I finally decided to chuck them out, having lots of others, but still.....they sounded so nice....and they were very familiar....you know the story, of course I kept them. I looked around eBay and found some ear cushions which were intended for an AKG K81DJ set - simply circular (toroidal). Although not meant to be glued on, these have a flat back face and can be glued successfully with Copydex latex adhesive. And they were the right size, 75mm diameter. They look fine and work very well in the lug protection role. The loose adjustment was awkward as the little housings are riveted and to get into them I would have had to destroy the outside face. Instead I found a couple of very strong tension springs about 10mm long, with looped ends, and stretched them across the face of the strip on each side and wired them behind the headband. This has the effect of holding the strip against the detent inside its housing regardless of the other clearances and is almost invisible (apart from the white ties, which I will change when I have something brown).
 

I can't do much about the cable without replacing it completely so I shall live with the existing one, at least giving me the advantage of being able to walk across the room without it unplugging itself.  Not much work involved but it means that my favourite headphones can continue to give me pleasure for a few more years. And that's probably all I've got myself anyway!

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