Pete B Posted April 7, 2006 Report Share Posted April 7, 2006 I'm rebuilding a pair of early - 1972, Masonite woofer and tweeter, 16/16 uF Rev1 crossover, Large Advents. These both had a fairly easy life, no tweeters ever failed, one woofer failed as a result of a solid state amp putting out full rail DC when it failed. I won't get into that woofer now as I didn't use it for this test. just let me say that the repair job done about 10 years ago by one of the big names was not very good - wrong spider, wrong dust cap, cone looks good, voice coil probably OK.Here's what I've done:1. Refoamed the good woofer and reported the T&S parameters in another thread. Note that RSSOUND foam gave very low and correct Fs and in system Fc.2. Remounted loose woofer XO inductor, used hot glue around the base for extra stick and to minimize vibration. Keep this inductor as far away from the tweeter inductors as possible to minimize coupling.3. Replaced internal wiring with 16 ga, Carol wire, eliminated wire nuts, and soldered directly to speaker terminals.4. Checked all connections, switch, and resistor with an ohmmeter, all was fine.5. Checked that the inductors passed a DC resistance check -fine.6. Removed both original Advent electrolytic caps.Wired up the tweeter normally, putting the original inductor across the tweeter, caps are still out of circuit. I used the original inductor since it is an odd high resistance unit and I wanted these to be completely original.Ran a bead of carpenters glue around all the internal box joints, and around the rear input plate.Replaced the fiber glass and closed them up using fresh mortite on the woofer. Tweeter screws were fine, woofer screw holes needed some repair.Outboarded the tweeter crossover, with an Eagle 3 ohm resistor and a 15 uF new Axon poly (two 7.5 uF in parallel) to one terminal post, and the original 16 uF electrolytic to another post also from the resistor. The other end of the resistor was wired to the front positive terminal on the tweeter.Power amp (100W high current) out went straight to the Large Advent to drive the woofer, and also to an A/B speaker switch. The A output went to one cap, and the B output to the other cap.The only replaced component is the Eagle resistor and it is shared, it measured 3.0 ohms.Note that the Axon was 15 uF and the original 16 uF, I did this simply because that was the available value, if this test showed a difference I would have paralleled a 1 uF.Playing music and switching, it was often as if the switch was not connected, almost nothing.During clapping (similar to broadband noise) in live music, and certain forward sounding recordings one sounded just a bit more forward. Very difficult to tell.Next, I tried pink noise from Track 15 Stereophile test CD #2. Obvious that one speaker was very slightly more forward.I expected it to be the higher 16 uF electrolytic, but it was the Axon probably due to lower ESR.I added resistance to the Axon and adjusted by ear, 1 ohm high, .5 ohm - high, .33 ohm - low, .4 ohm made them so close I'm certain it would be impossible to tell the difference.I'm not trying to prove anything about 15 uF vs. 16, I just chose the closest value and prefer to round down most of the time.I'd say that the difference without the .4 ohm resistor would be inaudible without the A/B switch and probably well within production variations for the original design. It was most often inaudible even with the A/B switch.I should probably point out that I tested a few of these original Advent electrolytic caps, after some use that might have reformed them, and they were within tolerance and had reasonable ESR. We also do not know if the ESR has gone up over time, it usually does and I might try some fresh Bennic electrolytics as another comparison just out of curiousity. Still, we are splitting hairs here, they might have had .2 ohms ESR when new in 1972 compared to about .4 now, not much of a difference and this is of course speculation.I'll probably include the .4 ohm resistor because I plan to use these speakers as a reference pair for the original stock Large Advent sound. I probably would not bother for speakers that end up for use in a workshop or background music system, the difference is so small.I did most of these tests without BSC:http://www.classicspeakerpages.net/dc/dcbo...sg_id=377&page=and without the "Increase" bypass cap thus in the "Normal" position. I did have both increase caps available, fresh Axon (15 uF) and the original electrolytic. I listened again with BSC and with both bypass caps coming to the same conclusion about the .4 ohm resistor. I didn't notice as much of a difference for the original electrolytic vs. Axon "increase" cap, but did not use A/B testing. Again, the system sounds much better with BSC.I would normally do a capacitor test with much better speakers, however, I did this quickly because there seems to be so much interest in, and controversy toward the Advents. I would normally do more measurements but these are not my primary interest.The results here are my observations and opinions, some will not take this as a conclusive test, it was good enough for my purposes.Constructive comments are welcome.Pete B. Link to comment Share on other sites More sharing options...
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