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Koss Pro4AA Renovation - How far should I go?

post #1 of 27
Thread Starter 
Hi All.

I recently got hold of some vintage Koss Pro4AA Headphones that I plan to restore. From what I have read, this model is reasonably well rated by their owners.

I'm pretty sure that I have one of the earlier models, the origional pads are there, though in need of replacement. There are a few things needing tidied up on these headphones so I am looking to renovate them to a point that I can use them.

Soundwise they are pretty impressive, even in their less than sterling condition. They seem easy to drive and have a good solid sound to them. A little crackle when manipulated, but other than that a reasonable sound.

Tonight I began their renovation. I have recieved some modern replacement parts via Koss's most excellent service network...

Some images...



At first glance they look in very good condition, but a closer look will reveal some blemishes!



The pads are I think the original oil filled items, but there is no oil in them now, just half full of air and not very comfortable to wear. I have modern foam filled replacement items from Koss's UK distributer!



The foam inserts have long since perished, All that remains is the mesh and grotty dust which is everywhere. The distributer managed to get hold of replacements!



The badges are missing, yep you guessed it, I have replacements via the distributer!


Some damage to the headband end caps. This had been glued to fix it unfortunately gluing the adjustment of the headband on one side. I have managed to release the leg now...



I also found that the cables are showing a little bit of corrosion in the left hand cup. Stripping back a little and re-making the connections can sort this I am sure if I opt to keep the original cable.



Here you can see the drivers, they are annotated with the number 822.

I have taken the phones apart and have started cleaning up the casework. The headband is cleaning up quite nicely. The colour is a sort of greyish cream colour. The current version looks more of a cream than this sets colour, does that seem right?

Now here is my questions...

One, what age are these phones likely to be? Is there a way of determining Year of Manufacture?



Any hints on bringing the finish on the cups back to origional? I have tried scrubbing them with washing liquid and I can see some improvement (the one on the left of the above image has been tentatively cleaned)... It's slow going though and I not sure if its more sympathetic to leave a little age on them... Thoughts?

Should I bother with re-cabling?

Assuming their age, is there any work that should be done to the drivers. You can see in the above picture that they are melted in place, I am pretty confident that I can take them apart and put them back together (hot glue?) but I dont want to get into it if there is nothing to be done...

Would they benefit from re-magnetising at this age?

Any other tips are welcome...
post #2 of 27
These would have been produced in the early 70's. I don't know of a way to tell the exact year.
post #3 of 27
Check with Koss and see if they will repair with lifetime warranty. Also they sell that vintage model currently still for about 99 bucks.

PRO4AA - Full Size Headphones - Koss Headphones / Stereophones - Koss

Happy listening!
post #4 of 27
I'm assuming that he wants to have a DIY adventure with this pair.

However, if the OP is not, I'm sure that Koss will repair them free of charge.
post #5 of 27
Thread Starter 
Quote:
Originally Posted by logwed View Post
I'm assuming that he wants to have a DIY adventure with this pair.

However, if the OP is not, I'm sure that Koss will repair them free of charge.
Yep, I prefer to do it myself. KOSS though supplied the parts FOC which I think is pretty amazing service.

I would love to know year of manufacture, but whenever it was, apparently it was before it became practice to batch mark or date mark components. The only distinguishing mark is that number on the drivers.

Anyone care to venture an opinion on the other questions, namely:

"Any hints on bringing the finish on the cups back to origional? I have tried scrubbing them with washing liquid and I can see some improvement (the one on the left of the above image has been tentatively cleaned)... It's slow going though and I not sure if its more sympathetic to leave a little age on them... Thoughts?

Should I bother with re-cabling?

Assuming their age, is there any work that should be done to the drivers. You can see in the above picture that they are melted in place, I am pretty confident that I can take them apart and put them back together (hot glue?) but I dont want to get into it if there is nothing to be done...

Would they benefit from re-magnetising at this age? "
post #6 of 27
Thread Starter 
Well I completed a gentle restoration on these cans a few days ago.

Got round today to write it up...

Koss Restoration article with plenty of pictures

What do you think?
post #7 of 27


 

Quote:
Originally Posted by justblair View Post

Well I completed a gentle restoration on these cans a few days ago.

Got round today to write it up...

Koss Restoration article with plenty of pictures

What do you think?

 

Thanks to your article I managed to repair a Koss Pro4AA that I've bought on an online auction. (It gave no sound from the right shell.) I managed to keep my apartment clean too, because you warned about the horrible dust that used to be the foam. :-)

 

The headphone is now back in working condition (clean and with proper connections), but only need a new pair of pads and maybe some foam for the inside (between the shell and the speaker).

 

Does the foam have a huge influence on the sound from the speakers, or is it there for insulation to and from the outside world only?

post #8 of 27

Pardon my butting in, but are you speaking of the foam between the speaker and your ear or the foam pad that goes around your ears?

post #9 of 27


 

Quote:
Originally Posted by SoundGoon View Post

Pardon my butting in, but are you speaking of the foam between the speaker and your ear or the foam pad that goes around your ears?


Ok, after re-reading what you previously posted, I'm guessing you mean between the actual speaker and your ear.  If that is indeed the case I would say that you do not need it.  I actually removed some of it on my 4aat's because it was muffling up the sound a bit.  I would say unless the headphone pressed against your ear uncomfortably while you have it on, you should be good. 

post #10 of 27

Soundgoon, thanks for your reply.

I meant the foam behind the speaker, inside the plastic shell. The foam between speaker and my ear is not replaced by anything and for me it does not influence comfort much. It gives it a nice clean look too, so I'll keep it like this for now.

The foam between speaker and shell most likely is there to damp out sound entering or exiting the headphone, but I was wondering if it does also influence the sound quality of speakers (other than reducing interference with sound coming from outside the shell).

post #11 of 27

I got a pair second hand but one of the drivers don't work.


Koss states "Stereophones that were purchased after July of 1989 are covered by our Limited Lifetime warranty."

but this one must be from the 70's.

Should I ask Koss to cover it or can I just buy the PRO/4AA elements and how much would that cost?

post #12 of 27

Well you just bought them right? Try and see if they will fix them for you. After all they were just bought ;)

 

Perhaps a wire has become loose internally. I can take a look at them for you though if you want.

 

The drivers themselves are cheap if I remember correctly. I think they were right around $25 each. I would recommend getting new drivers for both channels though.
 

Quote:
Originally Posted by tmblack View Post

I got a pair second hand but one of the drivers don't work.


Koss states "Stereophones that were purchased after July of 1989 are covered by our Limited Lifetime warranty."

but this one must be from the 70's.

Should I ask Koss to cover it or can I just buy the PRO/4AA elements and how much would that cost?

post #13 of 27

The voice coil is bad, no simple cure. But I did indeed just  buy them!

post #14 of 27

Print a receipt and and send it along with them. They should cover that. If not I live near Koss and can ask for you.

post #15 of 27

Well they are second hand and from the 70's era.

Can you ask them if they can cover new drivers, I'll promise to do a nice writeup!

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