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Found 4 results

  1. I was describing how crossovers work, in a general way, to a friend and decided a graphic portrayal would work best. I use LTSpice when I'm doing simple amplifier circuits and the like but I found an online tool which impresses me with its Java/JavaScript quality and suitability to the task of explaining multi-way speakers. The application site (a beauty of this is that it is a site, not an application you need to install on your PC or Mac) is http://www.falstad.com/circuit/circuitjs.html . If you click on this it will take you to the site with a simple RLC circuit already loaded. To take a look at the AR-90 crossover, you just need to load the parameters from a text file which I've attached. Here's the drill: * Once on the www.falstad.com site, click on <File>, then select <Import from Text...> to open a small dialog into which you'll paste the text file's contents. * Open the attached "4 Way Circuit - AR 90.txt" file using something like Notepad (the Windows app). Select the entirety of the file by using <Ctrl><A> and <Ctrl><C>, then paste the contents into the small dialog box opened in the first step above. Click <OK> and the model of the AR-90 crossover will appear. * Click the button labeled "Run / STOP" to see the frequency run from 20Hz to 20KHz while the simulation shows both the activity in the circuit and the resulting voltage delivered to each of the drivers (or in the case of the woofers, the pair of drivers). Note that I simplified things by only plugging 4 ohm resistors in rather than making any attempt to model the drivers ... remember this was just a simple teaching exercise. You may toggle the switches to see their effect on the voltages presented to the driver's surrogate resistors. Here's a picture of what you should see if you follow the directions above. Editing the circuit is very easy so, if this intrigues you, you may choose to model other crossovers by altering the topology/components. Thanks to RLowe for his contribution of the AR-90 crossover layout from which it was much easier to read component values than the other documents in the library. John 4 Way Circuit - AR 90.txt
  2. Well, I had been warned by many here that my beloved 38 year old AR-9's would eventually need to have their crossovers recapped. I was listening to a quadraphonic SACD on my system (The AR-90's are the front speakers and the AR-9's are the surrounds) when I noticed reduced output from the right rear AR-9. I immediately stopped playing the music and used a white noise test tone on the speaker. The tweeter not only had reduced output but was crackling away. Miraculously, I was pleased to discover upon re-capping that the tweeter DID NOT BLOW. Perhaps these tweeters are very robust, or perhaps the bass-free rear channels of the quadraphonic SACD saved it, or maybe I just dodged a bullet. Anyway, I replaced all of the upper range capacitors. The three smallest capacitors are Dayton PMPC (1%); the 30uF and 40uF caps are Dayton DMPC (5%); the 24uF cap is a Solen (5%) and the 80uF cap was replaced with a Jantzen 82uF (5%). I used Dayton or Janzen wherever possible as I understand that the Solens sound a bit brighter based on what I've read in these pages. I sent the old Callen capacitors, except for one of the 6uF units, to my cousin for measurement. The results are shown in the attached diagram: - One 6uF cap was off by 400%. This is the one that probably had failed and caused the immediate problem with the tweeter. - Both 30uF caps were way off by over 40%. - All the 4uF and 8uF caps still measured very close to their ratings. - The 24uF, 40uF and 80uF caps were in the range of 20% or less than nameplate. Given that both of the the 80uF caps were very close to each other at +15%, I suspect that they have always been that way. It is interesting to note that the AR-9's now sound somewhat clearer the the AR-90's but the 90's sound a tad sweeter. The AR-90's are a bit more forgiving and sound better with crappy source material while the AR-9's are more revealing and sound better with great sounding source material. Regardless, the upper range crossovers of the AR-90's will get redone next month as doing so is inevitable. Much thanks to all of you who provided input on this site regarding recapping these speakers. It was very helpful. AR Surround
  3. A quick question for those who know. Early today I got a lovely, consecutively numbered, pair of AR-90s, all grills intact, cabinets' finish in very fine condition, and six totally shot surrounds. I've taken care of the surrounds but was surprised by two things: 1) There is no stuffing in the enclosure holding the woofers. 2) The stuffing in the chamber for the lower midrange is VERY tightly packed, so much so that one has to push down on the driver (lightly) to mount it. They sound great, far superior to my AR-3as, AR-92s and AR-2axs, more articulate vocals, solid imaging, and, of course a bit more extended bass. From all appearances they were "factory fresh," I.e., I was the first one to remove the drivers. I remain curious about the absence of stuffing in the main enclosure since all my other ARs have had this. Any insight on the engineering/production decision(s) that led to this? Thanks, John
  4. Yesterday I got to replacing all the caps on the LMR, UMR, HF crossover board in my AR-90s. I did this with the crossover boards in place. I found it quite easy to get adequate access by removing both woofers and using a small flexible neck lamp to give me great illumination. I purchased the caps by mail from ERSE. They arrived promptly and all are 250V but in spite of this their sizes were suitable for replacement in the same locations occupied by the original caps. ERSE didn't have a 40 uF cap so I bought their 39 uF caps and parallelled with a couple of old GE nominal 1.2 uF caps I had already. The values in the attached screen clip include the 39+1.2 uF caps in parallel. You'll see that the original caps that measured significantly differently from their nominal values all did so on the high side. One of the black and red caps, an 8 uF one, had started leaking a white substance, otherwise all the original caps looked fine. I had planned to leave one speaker as it was and then measure for before and after comparison but decided to just get the project done and listen to music instead. I may get around to measuring the results eventually but have numerous other projects. Do they sound different? Maybe, but I'm suspicious of my being susceptible to wanting to hear an improvement ... the truth is I enjoyed them before and do now also. If anything, based on a few hours of listening, I sense a bit more stable positioning of soloists, either vocal or instrumental. Anyway, I'm pleased that the replacement was easy and that I don't have to worry about capacitor failure for the tops of these speakers. I'm driving them with a Sansui AU-D11 integrated amplifier I recently rescued (multiple issues but I really like the Sansui engineers' pushing of the envelope on this and the AU-D9 with their incorporation of output stage feed-forward and consider these two amps to be really lovely to listen to - I have one of each). Source material comes in directly from a Thorens+SME+Ortofon MC20 or via an Emotiva XDA-2 from CD, server, or MOG. Now to decide how to thin out my AR inventory - I've got two pairs of 3a, a pair of 2ax, a pair of 92, a pair of 4ax, and or course, the 90s.
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