2014 headphones Koss Pro/4X Plus - specifications and tips

[Kiriakos GR]

This topic is dedicated to the owners of Koss Pro/4X Plus and similar headphones.

KOSS Pro/4X Plus is one of the most amazing sounding headphones, I got my as used at 13/5/1993, and actually I buy them as used from a relative of my, who owns a business selling professional sound equipment.
At that time I did review in his shop all the best available at high pricing, and all failed in my test, then he told me.. wait... I will give you to test the ones that I use in my recording studio, but they are used.
I said I do not care, and he gave these KOSS Pro/4X Plus, they sounded as true magic in my ears.
Back then I was having a small studio broadcasting in FM radio, and a pair of robust and clear sounded headphones it was a must have.

At that time three pairs of cheap headphones failed in my hands due burned speakers or a failed cable plug, with out apparent reason.
Therefore I walked in that shop so to get something really expensive.
The money that I spent for them back in 1993 were by estimation an equivalent of one week income due labor.
But I never regret it. 


Intro 
Koss Pro/4X (Not Plus) is the first and older product of this series with an release year 1981 and is not actually comparable in performance with the latest 'Plus" model.

Koss Pro/4X Plus released at about April 1986 in USA with a retail price of $85.   

Koss Pro 4X Plus - product specifications:
Frequency response:  5 Hz - 40 kHz
Impedance: 108 Ohm
Digital ready .. translates as capable to cooperate with CD Players = modern design     


The Koss Pro/4X headphone combines a dynamic driver (rare earth magnet) with a piezoelectric tweeter.
Specially designed air cushions seal out external noise, cushions are air-filled and made by vinyl.
Pro/4XPLUS is housed in a high-impact packaging.

Repair Tips:

a) Air-cushions
These cushions are made by vinyl and their design has close example the air bag design.
As long vinyl is not punched by sharp object or sliced, all air pushed in from the factory stays trapped and does it job.
Therefore in case of small damage you may gently inflate by mouth the cushion and add over the hole few  drops of super-glue (15 seconds glue) which will take care the problem.

Air – cushions replacements are not offered by Koss, the company erased from it memory all old models (anything older than more than 10 years from today).
Therefore there is no life time warranty plan.

b) Air-cushions removal
These cushions are attached to the housing by the use of dual side sticky tape, which is very high quality.
Even so by just pulling the cushion with force, it would come off with out permanent damage to it.
By pulling out the cushion most or all sticky tape will stay intact, and all of it will stay glued over the cushion, instead of staying over the plastic housing.
The original glue does not lose it ability to stick back by one single removal, therefore you may reattach the cushion and it will stay in place, glue will hold about 80% of it.

c) Internal foam board replacement.
There is a slice of grey or black foam that it is possible to deteriorate due the years, or faster than that if headphones stay stored in a cabinet that is also stored in it acids as for example polish nail remover.
In my headphones the foam looks still good but not perfect.
To replace this foam is rather easy, after removing those cushions there is four screws in the corners, unfortunately they are polygon type and need a 3mm polygon tool socket type which I do not have either, my polygon keys set stops at 4mm, and therefore you need to use a pair of flat pliers and demonstrate additional patience.

This foam serves as air filter and also aloud more speaker movement regarding bass frequencies’ (sub woofer concept).
New foam is possible to come up for free as it is widely used in the packaging of new computer components.
Or it can be replaced by sponge, but common sponge has very short life cycle.


d) Air-cushions replacement
As long the original cushions are not available, you may replace them easily with any cushion with size of 95x80 mm, by having search eBay for two days, found only a close replacement at 95x77 mm which is almost the right one, and regarding pricing they are at about $9 for a pair (shipped).

To attach back the new cushion I will suggest 8 drops of super glue at key points or for a more professional job to use SEKISUI #5760 Double-sided Thermal Conductive Adhesive Tape.
By selecting the SEKISUI product you may easily replace the cushion as many times is needed.

Modern made cushions have a short life of 2-3 years and therefore you may continue keeping your headphones in good shape even with these cheap substitutes which are better than nothing.

e) PU Leather vs True leather.
By researching this and the all story about large headphone ear pads, there is two main concerns a) durability b) hygiene.
Regarding hygiene the original Koss Air-cushions (Vinyl) are second to none even today.
Their durability for 20 years is also astonishing compared to modern headphones which most of them comes by the idea that they are disposable.

Currently I have two alternative paths to follow, economy soft cushions & SEKISUI 5760 tape OR to locate cheap industrial earmuff (Noise Reduction / headphones style housing), which come with vinyl or similar ear cushions.
 
 
In summary, there is a second life available for the magnificent KOSS Pro 4X Plus, and the spare parts are not costly at all.
You will need to take a small personal risk about improvising a bit, but in the end, very few things can go wrong and the chances are 90% to restore back your headphones in their original condition.
Despite the current philosophy of disposable products, KOSS Pro 4X Plus was made in a time that repairing products was an option.
And so I am encouraging you to try to repair them by your self, or by asking one of your friends with technical background so to assist you.




The only problem of this pair after all these years is the vinyl used for the cushions gets stiff from age.
Second problem is that vinyl traps body heat and causes sweat.
In the positive side of things is that vinyl is waterproof.

[giorgos]

I can see in the second picture that your amplifier is a Κenwood KA7020.
I own a Kenwood KA3020 since 1993, which is probably same generation with yours.

[Kiriakos GR]

I can see in the second picture that your amplifier is a Κenwood KA7020.
I own a Kenwood KA3020 since 1993, which is probably same generation with yours.

I do not remember your model but you may compare my receipt (August 1993) so to evaluate the similarities. 

2x115 RMS with separate transformer per channel, plus active protections against shorted speaker, or full volume accidental start up.
Therefore it protects him self and the speakers by him self.
 
Hey my amp had it birthday four days back, 20 years old, and still has Low ESR inside it.