r_laski Posted January 23, 2020 Report Share Posted January 23, 2020 It’s been a long time since I posted on this forum. After several years without an audio system my better half urged me to replace whatever needed replacing and get back to enjoying my music collection again. I have two pairs of AR-9 speakers. I am using one pair of these in my “new” audio system. I knew part of my system rebuild would be recapping a pair of AR-9s. I spent a several days on this forum reading every thread I could find on what you all have done with your AR-9s. Thank you all for the wealth of information. I found it helped me develop a plan for recapping my AR-9s. Years ago I downloaded and saved all the AR-9 engineering drawings that were posted at the time. Glad I did as I couldn’t find them again on this web site. I also spent considerable time researching various types (electrolytic/film), brands, and sources of capacitors. I also found some valuable information on a few crossover component sellers’ websites / links. Below is a rundown of my project. Scope/Considerations: Some things I considered for the AR-9s: 1. Internal or External crossover. I decided to keep the crossover internal. There is only a minor change to how it is configured. Each Crossover section remains as originally laid out but is built on a separate pegboard. 2. What crossover parts to replace / retain. I decided to reuse all inductors and left the switch board as is. I replaced all capacitors, 6 Ohm resistor in the upper mid-range (UMR) crossover, binding posts, and all internal wiring. 3. Capacitor selection. Due to size and cost, woofer crossover capacitors are electrolytic with film bypass capacitor. All other capacitors are film capacitors (details below). I replaced the original wires with color coded 16 gauge tinned copper wire. 4. Cabinet changes. The cabinets are in such great shape I left them as is. The only “modification” was removal of plastic Velcro dots on tweeters and upper mid-range drivers and cabinet. I did not remove the original crossover backboard. 5. Drivers. Years ago I re-foamed all the 12” and 8”drivers in both pairs of AR-9s. The foam surrounds are still in new condition. Thanks to the speakers being boxed up or covered up while stored during a long period of non-use . I attached adhesive backed gasket tape to all drivers prior to reinstalling them in the cabinets during final reassembly. Crossover tear down: I removed nuts securing woofer/Lower mid-range (LMR) crossover boards removed them intact. This one had the small axial 470uF capacitor. The other AR9 had the large 470uF radial can capacitor. Before removal of any component from a board I took many pictures and labeled what each wire inductor lead and capacitor lead was connected to. I removed everything on the UMR/High Range crossover board without removing the board from the cabinet. Then the worst task of the entire project – removing hot glue from all inductors. Original capacitors measurements: I used the same basic capacitance meter I used when I recapped my AR-11s years ago. It tests at a single frequency, but for me that is enough to indicate whether a capacitor is in or out of specs. Below is a chart of capacitor measurements from both AR-9s in this project. Capacitor AR9K013212 Dif % AR9K013494 Dif % 2500 2250 -250 -10 2330 -170 -6.8 470 576 +106 22.6 510 +40 8.5 80 106.4 +26.4 33 151 +71 88.75 40 48.1 +8.1 20.25 40.7 +.7 1.75 30 50.5 +20.5 68.3 65.4 +35.4 118.0 24 33.0* +9.0 37.5 27.1 +3.1 12.9 8 9.31 +1.31 16.375 8.79 +.79 9.875 6 5.94 -.6 10 5.57 -.43 7.17 4 4.07 +.07 1.75 9.25 +5.25 131.25 * Capacitor reading was unstable, continuous changing. No doubt in my mind new capacitors would improve these AR-9s. Only one capacitor in each speaker measured within my threshold of within +/- 5% or rated capacitance. I spend a considerable amount of time deciding what capacitors to use for this rebuild. I considered capacitors I used for AR-LST, AR-11 and AR-90 recaps in the past, what others in this forum used, and what capacitors are being used and recommended by professional crossover builders/re-builders. I made several cost comparison spreadsheets of capacitor brands from various sources. I benefited from a 25% off seasonal sale on all the film capacitors I chose. It took purchases from 4 different sources to get all these capacitors. I decided on the following combination of capacitors: 2500uF - M.D.L. (Jantzen) (2) 1000uF and (1) 500uF electrolytic bypassed with 0.1 uF Clarity Cap CSA 630VDC film. 470uF - Mundorf E-Cap AC Raw electrolytic (matched pair) bypassed with 0.1 uF Clarity Cap CSA 630VDC film. 80uF - (2) 40uF Clarity Cap PX 250VDC. 40uF - 40uF Clarity Cap PX 250VDC 30uF - 30uF Clarity Cap PX 250VDC 24uF - (2) 12uF Clarity Cap CSA 250VDC 8uF - 4.7uF + 3.3uF Clarity Cap PX 250VDC 6uF - (2) 3.0uF Clarity Cap CSA 250 VDC 4uF - (2) 2.0uF Clarity Cap CSA 250VDC Note: Woofer capacitors are electrolytic bypassed with 0.1uF film. All other parallel capacitors are Clarity Cap PX film to save cost. All other series capacitors are Clarity Cap CSA except for 80uF LMR series capacitor. PX was selected to save cost. At the sale prices, the Clarity Cap film caps ended up costing about the same as a regularly priced set of Solen film capacitors would have. Prototype: As I stated above, I built each driver’s crossover on a separate pegboard. Preliminary layout Final layout - Holes in 4 corners of woofer pegboard match up perfectly with mounting studs in bottom of cabinet. Homemade bus bar of 14 AWG tinned copper. On the second AR-9 crossover I stacked the 500uF cap on top of the two 1000uF caps to reduce space and moved the bus bar over. This enabled me to move the entire layout down one row of holes and still have the corner holes open for the mounting stud in the cabinet. This also gave me more space between this board and the LMR board mounted behind it on the back of the cabinet. Crossover from second AR-9 (big can 470uF) and new woofer crossover - I tried to orient inductors in different planes as much as possible on each board and across boards. Original AR-9 LMR section (lower left quadrant) and new LMR crossover. The new board is mounted to the back of the cabinet below the UMR (original backboard). Woofer and LMR boards mounted in cabinet. Best effort to orient inductors in different planes between the two boards. UMR and High Range (tweeter) capacitor pegboards. UMR is built around original binding post holes. One side of pegboard holes had to be enlarged for all binding post holes to line up. UMR and tweeter boards in cabinet. Close-up of tweeter and top of UMR pegboards. One blue wire on tweeter board goes to tweeter. Second blue wire goes to black (-) binding post. Originally inductor and blue wire were connected directly to black (-) binding post. Wires: With few exceptions I kept all new internal wires the same length as the original wire lengths. However I changed some of the wire colors for convenience/ standardization. All woofer section wires were red (+) / black (-). I changed the wire from the upper red binding post to the switch board from white to gray. I kept the purple wire color from the switch board to the 80uF cap on LMR crossover. All other LMR wires were white (+) green (-). All UMR wires Orange (+) brown (-) All tweeter wires yellow (+) blue (-). Final assemble and testing - While I was working on the project AR-9s, I hooked up my other pair of AR-9s to my new audio system to “break-in” the new components and establish a subjective baseline of what an original pair of AR-9s sound like. I have to say, not knowing the actual condition of the capacitors in this pair the sound was very good. However, “s”, “t”, “st” harshness was very evident. I also had to switch the UMRs to -3db to tame its overpowering the other drivers. After reassembly I replace the left original AR-9 with recap project AR-9. All switches on the recapped AR-9 set to 0db. No burn-in. Just put some music on and subjectively listen. Immediately there was a noticeable difference between the left and right speakers. The left was a little louder, MUCH cleaner. The original AR-9s sounded pretty good by themselves. Compared to the recapped AR-9 however, my impression was the original AR-9 was now somewhat “fuzzy”. They sound between the two speakers was unbalanced. Putting the UMR switch on the original AR-9 to 0db balanced the output somewhat. But, it did not improve the difference in clarity (no pun intended). I rebuilt the second AR-9 crossovers making minor changes in the layout. One significant change I made was to glue machine screws to the spacer boards. I put spacers under the crossover pegboards to provide space under the pegboards for the cable ties that secured the capacitors and inductors. Now all crossover boards are secured with screws, washers, and nuts and can be removed. Only the spacers are glued to the cabinet in this AR-9. Listening with both recapped AR-9s hooked up: I’m not a GESR (golden-eared stereo reviewer). All I can say is I’ve never owned an audio system that sounded this amazing! I remember when we were recapping AR-11s, AR-90s and LSTs. We would describe the improvement as being as if a veil had been removed from in front of the speakers. This is more like a heavy curtain has been removed. Female and male singers sound like they are standing in front of me in the room. Background vocals are distinct from the lead singer. There is air and space between instruments and around each instrument. As familiar as I thought I was of my music collection, and I can’t believe I’m saying this, I heard things I never heard before in the music. Quote Link to comment Share on other sites More sharing options...
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