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Numark Electret/Electrostatic ES-701 converter question

post #1 of 8
Thread Starter 

Hello all, 

   I purchased a set of Numark ES-701 headphones with a broken plug.  The cables have only 2 conductors per side making them electrets, the 6 pin plug is just for show and to ensure polarity.  My issue is I do not have the converter box to find out the rating on the transformers.  If anyone out there has a photo of the inside of one of these converters, they were also sold under the K-Mart brand and radio shack.  I would like to build the converter box.  Very little information out there.  

post #2 of 8

Hey there - I just purchased a set of the Numark headphones (with the ES-701 energizer) and I'll be glad to post photos of the inside of the unit when I get them.


I believe these were a OEM Stax headphone set made for Numark (Stax made quite a few variations of this set for other leading hifi brands).


This is my first post (though I've ended up here on Head-Fi quite a number of times) on this forum but hopefully the mods will allow me to upload some pics for you to see.


I've actually got a small collection of some very nice vintage headphones (1970's-1980's) and would be glad to share some other photos sometime in another thread too. Anyway, when the Numarks arrive, I'll be glad to take some photos (only if you're interested, please post to let me know you're still interested so I don't waste any time).

post #3 of 8
Thread Starter 

Hello, and thanks for the response, some pictures of the energizer unit's insides would be great.  I am still trying to find a set of the step up coils, and this will give me some clearer idea of what I am looking for, size wise.  

thanks again.

post #4 of 8

Hi and it would be my pleasure to help. I hope someone here on Head-Fi might be willing to do the same for me in some way sometime.



The small adaptor-amplifier dimensions are (not including rubber feet) approximately 5-inches long/deep, 3-inches wide, and 2-inches tall. The whole unit weighs exactly 3-lbs.



I took a series of photos for you to view and embedded them into the thread here. They are also viewable on Photobucket at the following link, but I know the pop-ups on Photobucket are highly annoying. I'll leave them live for a while so that they will remain viewable for a time. You should be able to download individual photos onto your PC/device for offline viewing later, in case you wish to save any of them for reference.



Let me say this for orientation reference:

When viewing the unit from the front (with the cover off) the RED WIRES run along the RIGHT SIDE and the BLUE WIRES run along the LEFT SIDE.



I took many many photos from numerous angles and just wanted to say that so as to clarify direction/orientation etc.



To me, it looks like the unit is comprised of 2 audio transformers & 2 ceramic disc capacitors (unknown values) and thankfully no electrolytic capacitors. Then just a switch & plug receptacle on the front & a terminal strip on the back. Neither of the transformers are marked in anyway that I could see. They both look to be of equal size etc.



Take a look - and hope this helps!











post #5 of 8

Oop, just editing this - the moderator(s) have since approved the above post with lots of photos  :beyersmile:



I do wonder (if anyone knows) exactly which Stax model was the equivalent?  From my other hobbies (stereo & radio communications) I know that most OEM manufactured items are often just either exact identical (just re-branded) equivalent models, or are special sub-models specifically altered to meet the desired specifications of the company ordering them.

Edited by Radar1 - 6/26/14 at 12:57pm
post #6 of 8
Thread Starter 

Thank you so much for the photos, this gives me much more to go on for my build.  I will post photos of the build when I get the step up transformers. 


post #7 of 8

You're quite welcome, glad to share. I wonder what the spec's are on the original xformers? It would've been nice if they'd been marked. I look forward to seeing what you come up with but don't forget there is most likely a Stax or other actual OEM equivalent for this energizer that you may find orphaned on eBay at a good deal

post #8 of 8
Originally Posted by sylr87 View Post

Thank you so much for the photos, this gives me much more to go on for my build.  I will post photos of the build when I get the step up transformers. 


Did you ever get anywhere with this project?? 


Not that it's dire - but I did check this thread a number of times on occasion,  in the hopes that you'd tried to get this project started or even accomplished.


It's a bit unusual that the transformers would go bad. What made you feel that they were no good?


I'd start any project like this by changing the capacitors first. There are only 2 ceramic disc caps, and though they have a much longer lifespan than electrolytic caps, they can degrade and need replacement after this many years.


As said above (in my large photo-laden post), my energizer had only 2 large orange ceramic caps and (unfortunately) their values weren't marked on them. Does anyone know their values?


If anyone on Head-Fi has a schematic for the ES-701 (OR it's equivalent - Stax was known for rebranding the same units for a number of other companies) I'd certainly appreciate it if they would (very kindly) scan & upload the schematic for myself & other Head-Fi members (I'd love to see the values of the ceramic caps, and I'm sure sylr87 would like to see the transformer numbers).


Hope all is well out there in Head-Fi Hi-FI land!

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