BEC Posted September 21, 2005 Share Posted September 21, 2005 This is an AL-3 crossover from a set of 1990 Lascalas Bob Crites Quote Link to comment Share on other sites More sharing options...
BEC Posted September 21, 2005 Author Share Posted September 21, 2005 This is an AL-3 crossover from another set of 1990 Lascalas. Bob Crites Quote Link to comment Share on other sites More sharing options...
IndyKlipschFan Posted September 21, 2005 Share Posted September 21, 2005 Kinda strange it is different isn't it? Maybe this proves that even in the same class, as parts became available (better we all hope?) Klipsch also used them as well. For some reason this number is in my head, the Klipsch KHorn was upgraded / modified over 63 times too. Anything is possible. Quote Link to comment Share on other sites More sharing options...
BEC Posted September 21, 2005 Author Share Posted September 21, 2005 The only real difference is that in the second one shown above, the tweeter protection includes the very expensive zener diodes like were used in the Type AA crossovers in the 70s. The one on top uses a much less expensive polyswitch for tweeter protection. The cost is really significantly different. Todays cost of the 4 zeners would be around $40.00 for the pair of crossovers compared to perhaps $2.00 for the polyswitch and resistor. The official schematic shows the polyswitch. Bob Quote Link to comment Share on other sites More sharing options...
Duke Spinner Posted September 21, 2005 Share Posted September 21, 2005 Well .... that sure Blows .... ifn' ya got tha wrong version........[] Quote Link to comment Share on other sites More sharing options...
Deang Posted September 21, 2005 Share Posted September 21, 2005 The polyswitch adds resistance -- the zeners don't. Quote Link to comment Share on other sites More sharing options...
mark1101 Posted September 21, 2005 Share Posted September 21, 2005 For the general discussion here, I might as well just say that the zener networks belong to me. The pair of LaScalas that they came from was exported to Rotterdam from Hope when new in 1990, and I purchased the speakers from the original owner. He was a soldier who brought them back to the states when he finished his duty. I had to drive a 16 hour round trip Georgia to Virginia to get them. They came to me in the original boxes, and the labels indicate this original shipping info. Maybe Klipsch used those zener mods for a reason on exported product. Quote Link to comment Share on other sites More sharing options...
colterphoto1 Posted September 21, 2005 Share Posted September 21, 2005 Klipsch has been using Zeners for quite a while. My LS Industrial splits have AL networks with the Zener's in them. Quote Link to comment Share on other sites More sharing options...
BEC Posted September 21, 2005 Author Share Posted September 21, 2005 I like the zeners. Just was surprised to see them in an AL-3. I wonder how many of the AL-3s may have been shipped with them. I think they are better in every way than the polyswitch. Every way except expense, that is. Bob Crites Quote Link to comment Share on other sites More sharing options...
colterphoto1 Posted September 21, 2005 Share Posted September 21, 2005 If the Zeners are so costly, should they be stripped from my AL's prior to trashing? Any other parts that should be salvaged from them? I noticed that you used Zeners in the AA/A's you sent me to replace the AL's in my LS's. Thanks for caring enough to use the best! Michael Quote Link to comment Share on other sites More sharing options...
BEC Posted September 21, 2005 Author Share Posted September 21, 2005 Michael, I have never seen any of the old zeners go bad. They are hefty 10 watt units. I would keep them. Of course, I never throw anything away as you would see if you tried to get into my shop. Bob Quote Link to comment Share on other sites More sharing options...
Q-Man Posted September 22, 2005 Share Posted September 22, 2005 I've had a lot of AL-3's, and I never had one with the zenders. Quote Link to comment Share on other sites More sharing options...
mark1101 Posted September 27, 2005 Share Posted September 27, 2005 Well, Today I got my AL-3s and Es back from Bob. He did his usual one day turn around. Now Bob has rebuilt all 4 pairs of my Heritage pairs. The Heresys had a marked improvement as I expected they would from their age. Same overall but mainly top end improvement I noticed on previous Es Bob did, and on my corns Bs. My son will be really happy when he turns them on. But....my 1990 LaScalas which are in my main system with the Peach and VRDs have improved in a much more noticeable fashion. I didn't really expect this since they are only 15 years old. I thought they sounded great already. They were certainly way better than my corns and the heresys are just not in the ballpark anyway. Right now I'm listening to them and they are simply cleaner and clearer than before. A superb improvement. I have also noticed an unexpected bass improvement (subtle but definitely an increase in output) which leads me to think I had a minor issue that I wasn't noticing. The first thing I did when I got things warmed up was turn down the subs. Go figure. Anyhow, thanks again Bob. An excellent job on everything but especially the AL-3s. By the way, here is an "after" picture. Quote Link to comment Share on other sites More sharing options...
mark1101 Posted September 27, 2005 Share Posted September 27, 2005 Whoa, sorry about the picture. Quote Link to comment Share on other sites More sharing options...
BEC Posted September 27, 2005 Author Share Posted September 27, 2005 I happen to have a picture also. Bob Crites Quote Link to comment Share on other sites More sharing options...
WMcD Posted September 28, 2005 Share Posted September 28, 2005 The Zener's were mentioned in the Edgar interview of PWK (and others). It might have been Jim Hunter who described it. The Zeners are in series back to back across the tweeter. The diodes don't conduct when back biased until they reach the "Zener voltage." The other one is naturally, forward biased, so the pair conduct to clip off (or "clamp") high level a.c. Arguable this is a scheme to put a short across the amp (and perhaps blow it) in an effort to protect the tweeter. My recall is that Jim said this was not a very nice thing to do to an amp, and the design was changed. I wonder if there were irate letters from people with burned out amps; or maybe some amps were lost during Klipsch back yard parties? Smile. There is a complaint that fuses do not act fast enough to protect tweeters; again the tweeter blows out to protect the fuse. My idea is that putting a fuse between the Zener clamp and the amp would work better. The clamp would blow the fuse quicker than the tweeter would and everyone wins. Gil Quote Link to comment Share on other sites More sharing options...
BEC Posted September 28, 2005 Author Share Posted September 28, 2005 Gil, The zeners do not short. They conduct once the voltage across them reaches 10.2 volts peak to peak. No matter how much more power is applied to them, they stilll maintain this voltage across them at 10.2 volts (up to their maximum rating which is 20 watts). A device maintaining 10.2 volts across it is certainly not a short. Even if they failed and did completely short, that would still not be a complete short to the amp. The signal would still be through 2 2uF caps and that would still not be a short. Bob Crites Quote Link to comment Share on other sites More sharing options...
WMcD Posted September 28, 2005 Share Posted September 28, 2005 I agree Bob. My use of the term "short" lacked precision. My visualization is that the amp may be trying to out 100 volts peak. If there is a, say, 10 volt Zener clamp across it with out series resistor, we have a bad situation. There is 90 volts across the internal impedance of the amp. If there was a load of zero ohms (a short), there would be 100 volts across the internal impedance. So there is a difference. The little popping noise, the white smoke, and silence, are delayed. Smile, Gil Quote Link to comment Share on other sites More sharing options...
BEC Posted September 28, 2005 Author Share Posted September 28, 2005 Gil, We have argued this one into the ground before, so I bumped that thread back to the top in this section. Title: Replacement 1n3996 in AA Xovers? Bob Crites Quote Link to comment Share on other sites More sharing options...
mark1101 Posted September 28, 2005 Share Posted September 28, 2005 All I can say about this is that I have never lost a tweeter or other driver, nor sustained any amplifier damage in 29 years. If I lose one anytime soon, I'll let you guys know. It is an interesting subject, however. Knowing less about the theory, my guess is that the zeners were discontinued due to cost. A $40.00 cost reduction per pair of speakers is a no brainer. Quote Link to comment Share on other sites More sharing options...
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