Ask about buying a used Koss and someone will tell you not to worry, because Koss fixes everything forever. The warranty is real and generous, but the written terms are narrower than that story. If you're buying secondhand, it's worth knowing exactly what Koss promises before you count on it.
What the warranty says
Koss publishes its terms on its warranty and repair page. In short, a Koss product with a Limited Lifetime Warranty is warranted to be free of defects in materials and workmanship for the life of the product. The promise is made only to the initial user or purchaser, and the page says it doesn't apply to an initial owner who lets the product be used by multiple people.
If something fails, Koss decides the remedy. It may refund the purchase price, repair the headphone or replace it. To claim, you send the headphone in secure packaging to the Koss factory in Milwaukee with a note describing the fault, your contact details and a small per-headphone fee for return shipping and handling. Koss asks owners to register their headphones too. Buyers outside the US go through the local Koss dealer instead.
Three more lines matter for vintage buyers.
- Discontinued models. Koss reserves the right to replace a discontinued product with one of equal value. Send in a 1970s pair and you may get a current model back, not your original repaired.
- Misuse. If a claim falls outside the guidelines, Koss will repair the product and charge for its time and materials.
- Not every product. The same page lists 90-day and one-year warranties for some products, and tells you to check the documents that came with yours. Koss's product pages say all its wired headphones carry the Limited Lifetime Warranty. Wikipedia dates the lifetime warranty to 1989 for headphones made in North America.
Does it cover a pair you bought used?
On paper, no. The terms name the initial user or purchaser, and nothing Koss publishes extends that to later owners. Some owners report Koss being lenient in practice, and you'll read stories of old headphones coming back fixed with no questions asked. Those stories aren't a promise, and the one we could trace came from an original owner.
So treat a used Koss as uncovered. If the seller is the original owner and still has the paperwork, that's a better position, but it's still their warranty, not yours. Price the pair as if any repair is your problem, and anything Koss does for you later is a bonus.
The swap clause matters even more for collectors. If you want a 1970s Pro/4AA or an old HV/X because it's the original, a warranty claim that sends back a current model defeats the point. Koss brought the Pro/4AA back after retiring it in the late 1980s, so a current one isn't a bad headphone. It just isn't the one you bought.
The electrostatic is different
The ESP/950, Koss's electrostatic from 1990, runs with its own E/90 energizer, and its current successor, the ESP/95X, has a separate Limited Lifetime Warranty page. That one also covers only the initial user, carries a higher fee and asks you to send back the entire product with all included parts and accessories. It also says any disassembly, modification or tampering may void it. The original ESP/950 manual called its cover a no-questions-asked lifetime limited warranty, but the current written terms are the ones Koss applies today. If you're buying a used ESP/950, assume no warranty and check that the headphone, the E/90 energizer and its power supply all work together before you pay.
What to check on a used Koss instead
With the warranty out of the picture, judge a used Koss the way you'd judge any headphone. Our guide on how to check used headphones covers the general checks. For Koss in particular:
- The cord. Most Koss models have a cable that's wired in. The Pro/4AA has a long coiled cord with a single entry, and one Koss reviewer whose 1970s pair stopped working traced it to a short in the cord. Ask the seller to play music while flexing the cord near the cup and the plug. Sound should stay on in both ears.
- Both sides. Ask whether both sides play at the same volume. One quiet side can be a failing driver or a broken wire, and on a pair with no warranty you'll be paying to find out which.
- Pads. Koss still sells genuine ear cushions for several current models, including the Pro4AA, the Porta Pro and the ESP/950. That makes worn pads on those models an easy fix. Older or discontinued models may have no Koss pads, so check them carefully in the photos.
- The ESP/950 kit. The headphone ends in a custom 5-pin plug that goes into the E/90's phones socket. The E/90 runs from an AC adapter or a battery box that takes six C cells, and its LED flashes red as the batteries run down. Ask for a photo of everything together and confirm the energizer powers up.
- The model. Koss has reused names and made many variants, from the Pro/4AAA with its D-shaped cushions to the many Porta Pro editions. Ask for a photo of the label so you know which version you're getting.
If you're the original owner
If you bought your Koss new, register it and keep the paperwork. A claim goes to the Milwaukee factory with a note describing the fault, your name, return address, phone number and email, and the handling fee. Koss says it ships warranty replacements within 72 hours of processing a claim.
The short version
The Koss Limited Lifetime Warranty is one of the most generous in headphones, but it belongs to the first owner. A used Koss is a good buy on its own merits, since genuine parts are easy to get for the popular models. Buy one for what it is in the photos, not for a repair you may not be entitled to. You can see every Koss we cover on the Koss page, or compare them with other closed headphones on the closed-back page.