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Acoustic Research AR-2ax MKP vs MKS vs Electrolytic


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Hello all
This is my first post on this forum. I am a  audiophile passionate about vintage and I bought two pairs of Acoustic Research AR-2ax speakers, in the two variants, the one with textile suspension and the other with foam suspension.
I would like to start by changing the capacitors, both pairs still having the original capacitors.
But here, what I read on the forum is somewhat contrary to my practical experience. I noticed that most of those who did this operation recommend changing the capacitors with MKP, polypropylene. I tried this with other pairs of vintage speakers and the sound was metallic, synthetic, similar to the sound of modern speakers. After multiple tests with MKP, MKS and Electrolytic Capacitors, I came to the conclusion that it sounds best with the same type of capacitors they were built with.
The AR-2ax speakers, from what I read, have two bipolar capacitors, 6 uf on medium and 4 uf on highs. Has anyone tried to change them with Electrolytic Capacitors, but of good quality, for example these?

Thanks and excuse my English, I'm from Romania.


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Hello Banga and Welcome

Have you downloaded the AR3a restoration guide?  Much of it is relevant to your speakers, which appear to be very nice examples.  Regarding caps: The cap arguments flare here once in a while but you can't go wrong replacing like with like, in this case NPE.


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Hi Banga

Let me add my welcome. And by the way, your English seems excellent.

Audio genius Ken Kantor (of AR, NHT) agrees with you. Replace electrolytic with electrolytic. But the Vishay-Sprague cap you linked does not seem to be bipolar. 

Several members here have reported good results with Mundorf e-caps. https://www.mundorf.com/audio/en/shop/Capacitors/Audio_Caps_ECap/ Unfortunately, finding 4uf and 6uF NPEs may be hard. I see Mouser has 2.7 and 3.3 radial NPEs that you could use in parallel for your 6uF.  The 4uF will be tricky. Maybe two 2.2uF? Personally, for those low capacitance values I'd use film caps.

Nice speakers!


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Aadams and JKent, thanks for the advice. I downloaded the restoration guide for AR3a and I also discovered on the forum valuable information for restoring these speakers in parameters. Initially, I bought two pairs thinking that I could get two good ones out of 4 partially functional speakers. I knew that the speakers with textile suspension had problems with the Aetna potentiometers from the person who sold them to me. But listening to these speakers, both versions, it was love at the first listening and I decided not to take parts from one pair to repair the other pair but to restore them all 4.
Regarding the capacitors, I kind of avoid the so-called Boutique Capacitors and everything that contains the phrase Audiofil - all these having artificially inflated prices, in my opinion. For example, in terms of cables, after I bought professional cables from Sommer, Cordial and Procab, I sold all the expensive audiophile cables from Neotech and Unison Research. Professional cables sounded better. Regarding the capacitors, I successfully used Epcos / TDK, Wima and sometimes Monacor. I understand that Vishay would be very good too.
The values being small (4 and 6 uf) and implicitly quite cheap capacitors, I will try all kinds of capacitors on these speakers. Of course I will keep you posted on my experiments.

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Great speakers Banga 

I picked up a pair late last year and started what you are about to, like you I was immediately impressed even in the rough state mine were in. I'm not the most tech savvy and trusted someone else with the cap selection - Russian paper in oil. I was very happy with the results but can't comment on change in signature as I only tested the originals for a few songs as the speakers had other issues that needed addressing before proper listening could happen. They are in no way metallic, even found them a little dull until I upgraded the tweeters which really brought them to life and deepened the soundstage.

Positioning also played a big part in the best results, try a number of positions, I'm sure every room will be different. It took me a while to get these dialed in but now the have been holding center court in my system for a few months. 

Looking forward to your findings and welcome to classic speaker

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Before my capacitors arrived, I ran into the Aetna rheostat problem at the pair with the textile suspension . I read that people recommend vinegar with salt and  mechanical cleaning of the  rheostats with a Dremel. Question: Has anyone tried to clean these rheostats with a special contact spray? It's like trying this option first. For example :
http://www.kontaktchemie.com/KOC/KOCproductdetail.csp?product=KONTAKT 60

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