Koss PortaPro4AAA - DIY KOSS high-end dynamic headphone :)
May 26, 2012 at 8:52 PM Thread Starter Post #1 of 14

jupitreas

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Hello all,
 
I've always been a fan of the famous KOSS 60Ohm driver used in the classic Porta Pro, KSC75, UR-40 and other headphones. This 60Ohm driver is perhaps the best example of an economic driver that delivers performance that is way above its price range. There are many mods of this incredible driver. Here is mine :)
 
I always wondered what a proper high-end Koss headphone would sound like. Obviously, Koss has the electrostatic ESP950; however, I really wonder what a high-end KOSS attempt at a dynamic-driver headphone would sound like. I decided I'd build something that would embody this idea based on KOSS' arguably best dynamic driver - the famous 60 Ohm driver.
 
Here is how I went about building this vision. I got a used, broken PRO4AAAT, which is the current high-end KOSS open dynamic model. I fixed it up (turns out it was just a cable issue) and realized that it sounds terrible. I decided to take it apart and realized that it would be fairly easy to transplant KOSS 60Ohm drivers into this enclosure. I ended up cutting up my UR40 and experimenting with all kinds of damping to get the best sound. In the end, I realized that it was best to leave this can as open as possible. I replaced KOSS' ridiculous vinyl pads with velour pads that I bought off of eBay (Beyerdynamic DT700 series would also fit). I also added a bigger, real-leather covering for the headband. Finally, my vision was complete: this is what a KOSS high-end dynamic driver, open-back, circumaural headphone should sound like :) I sure hope that KOSS takes some advice from this and makes a proper dynamic-driver behemoth, since this is definitely a company that deserves some success. All hail KOSS:)
 
Lets move onto the sound for a little while. These bad boys basically sound very similar to the PortaPros and the KOSS UR40. Compared to the PortaPro, they have a signifcantly better sound-stage. The bass is a little deeper but not quite as well defined (it is still relatively clear though). The mids and treble are unchanged from the PortaPro but there is more high frequency extension available and this is sometimes (but rarely) noticeable in some very well-recorded albums or games that use wide dynamic-range special effects (Mass Effect 3, Dark Souls). Generally speaking, I'd classify this as a relatively flat can that adds a lot of fun/bombast to whatever scene it is used for. It is a fun can but not extremely so.
 
Here are some pictures, I'll post some more detailed pics of the innards soon. Please go ahead and ask me any questions you might have :)
 

 

 

 
May 26, 2012 at 8:58 PM Post #2 of 14
Nice driver transplant. I've been wondering about doing something similar with a Audio Technica headphone and the PortaPro drivers.

Does the UR series of headphones have the same drivers as the PortaPro? If so, I was unaware, as I disliked the UR model on display at B-Buy when I compared it to my PortaPro.
 
May 26, 2012 at 9:19 PM Post #3 of 14
Does the UR series of headphones have the same drivers as the PortaPro? If so, I was unaware, as I disliked the UR model on display at B-Buy when I compared it to my PortaPro.

It is the same driver but the diagrphgm is coated with titanium. This titanium covering gives the UR40 (and KSC75, which has the same driver) some more resolution in the high frequencies, while also adding a slightly metallic sound. The non-titanium version still has great clarity while also not sounding metallic, like the titanium versions
 
May 27, 2012 at 8:00 AM Post #5 of 14
I hated the original vinyl earpads of the PRO4AAAT as well. They were very uncomfortable, got sticky very quickly and didn't really offer any isolation either. This is why I went for these velours instead and I am very happy.
Quote:
Very cool!! I have the older PRO4AAA, and have considered doing a driver transplant myself. The stock earpads (like this one) seem to really mess the sound up..

 
May 29, 2012 at 1:47 AM Post #8 of 14
I think these are it! just bought a pair.

http://www.ebay.com/itm/Replacement-Cushion-Fit-Superlux-HMC660-HMD660-HMC-HMD-660-Headphones-headset-/251068575271?pt=US_Headphones&hash=item3a74da6e27#ht_1323wt_1114
 
Jun 5, 2012 at 10:42 PM Post #10 of 14
How can you?
The pro4aaat shell is so badly designed with a lot of resonance and work properly only with the 250Ohm closed back driver.
Koss made better 60 Ohm drivers for the the ESP Enclosure. 
 
Jun 6, 2012 at 3:37 AM Post #11 of 14
The Pro4AAAT shell works pretty well with the smaller 60 Ohm driver. The driver is about the same size as the hole in the back of the enclosure, making this design a fairly open one, without a lot of resonance.
 
Jun 17, 2012 at 12:38 PM Post #14 of 14
I am using some microcell foam from an inkjet printer cartridge + some blu tak on the rear baffle. The SFI drivers I used need dampening to sound decent, IMO.
 
Wonder if the portapro drivers you used would work in closed back..
 

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