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Youthman

Possibly Have a Bad AA Crossover in One LaScala - Need Help

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Looking for some help / advice as you guys are much more technical than I am.
 

Short version...


1) I ran Dirac Live on the Monolith HTP-1 processor and after the calibration, I discovered the left speaker measured quite different than the center and right original LaScalas (1980 model).

 

2) Using REW and UMIK-1, I measured the Left, Center and Right speaker. The center and right had similar frequency responses but the left speaker measured quite different.


3) I swapped the left and right tweeter

 

4) Took new measurements. The center and right speaker had a similar frequency response, the left speaker measured quite different

 

So this tells me the tweeter is not the issue.

 

5) I took three nearfield measurements to try and take as much of the room out of the equation as possible and pretty much had the same results.

 

Below is a video showing measurements from #2-4 above.


I'm editing a video now of #5 above and will share it in this thread once I get it edited and will post it here as well.

I'm thinking the crossover in the left speaker is faulty and will need to be repaired / replaced. Let me know if there is any other testing I should do before purchasing another AA crossover.
 

 

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Disconnect one of the KLiP diodes in the network giving trouble and retest.  If that's not it, isolate the tweeter inductor and measure its resistance and inductance (disturb it as little possible so you don't change any defect it might have).  Retest.  If that isn't it, test the ESR of each tweeter cap.  If you can't measure ESR, replace the caps one at a time with high quality film and foil caps. 

 

I predict it is the diodes.  If you are not running AlNiCo K-77 tweeters, disable them in all of your La Scalas. 

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29 minutes ago, JohnA said:

 

 

I predict it is the diodes.  If you are not running AlNiCo K-77 tweeters, disable them in all of your La Scalas. 

you are right about the possible zener diode going bad    ,  but  you are saying the Square magnet   ferrite K77-EVT35  does not need that  protection  but the Alnicos do -----can you elaborate -please Tx --

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Sorry fellas, that's way over my head. Any chance of getting that in layman's terms?

The crossovers are all AA and the tweeters are all K77M.

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You could swap crossovers to be sure that is the problem then send it to Bob.

What caps are in them now? 

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9 hours ago, Youthman said:
Sorry fellas, that's way over my head. Any chance of getting that in layman's terms?

The crossovers are all AA and the tweeters are all K77M.


8c1e9a3ad778f75f004bccb41b495da3.jpg

I will attempt layman’s terms...

The zener diodes are the two things on the metal bracket in the center of the photo above. Each of them has a wire that goes to the tweeter part of the terminal block. Disconnect at least one of those wires.

Those devices clamp the signal going to the tweeter should there be an overvoltage transient, thereby protecting the tweeter from damage. That’s the idea, anyway. The can go defective and that could affect the frequency response. Some people don’t like them in the circuit at all.

I’m not certain what parasitic effects these might have during normal, correct operation.... you might not get exactly the same response when you’re done between the center / right and this one once you take the diodes out of circuit. If it fixes the gross curve error, you probably found your culprit.

Please post results

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BTW, If Dirac is named after Paul Dirac,then I’m pretty certain you’re pronouncing it wrong.

It isn’t DIE rack, it is DIR ack or perhaps DEER ack

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You can jumper across them with some jumper wires and see if they are the problem. Will not hurt anything as long as you do not play overly loud. The original AL-3 crossovers in my speakers that were from all accounts supposed to have them did not. Perhaps they were just out of them when my LaScala's were built. I doubt they are the problem though. Bad solder connection or just bad connection from amp to crossovers might be. Swapping crossovers with speakers would be an excellent test. Check all connections first. 

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I would just build new type As with caps from BOB. Take them diodes OUT ........More simple more better...lolTypeA.jpg

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55 minutes ago, henry4841 said:

You can jumper across them with some jumper wires and see if they are the problem. Will not hurt anything as long as you do not play overly loud. The original AL-3 crossovers in my speakers that were from all accounts supposed to have them did not. Perhaps they were just out of them when my LaScala's were built. I doubt they are the problem though. Bad solder connection or just bad connection from amp to crossovers might be. Swapping crossovers with speakers would be an excellent test. Check all connections first. 

Sorry, but jumpering across them will not tell you anything except that you have good jumper wires.  They are paralleled across the tweeter.  Jumpering across them would cause the signal to at the tweeter to disappear completely.

 

 

typeaa.jpeg

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Youthman, your in Kissimmee ?
If you can’t get it worked out. I could lend you a hand. I’m about 1.5 hour drive


Sent from my iPhone using Tapatalk

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Thanks Carl. I'm in Plant City. You can see it listed under my profile photo.

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11 hours ago, Youthman said:

Sorry fellas, that's way over my head. Any chance of getting that in layman's terms?

The crossovers are all AA and the tweeters are all K77M.

you should buy 2 of these diodes and swap them out on your  AA crossover as 1 or 2  onboard may be defective  - 

 

-currently what you can do is bypass the Zener diodes by removing one of the red wires or both ,that are connected to the diodes via the terminal strip  

 

-  this will deactivate the diodes that protect the K77 Tweeter -but as 1 or 2 may be bad  ,  by doing so ,  the sound quality should be back to normal IF  the diodes are the culprit  -

 

https://www.ebay.com/itm/Genuine-Microsemi-1N3996A-5-1V-10W-5-Zener-Diode-DO-4-Package-Hardware-Included/192753974618?hash=item2ce1083d5a:g:PnIAAOSw4VpcDnSh

 

 

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Thanks Carl. I'm in Plant City. You can see it listed under my profile photo.

I mist that.

I use Tapatalk on my phone. This is what it shows. 1ea6c0b86d9ac603bfccc686a87347d5.jpg

Lol

 

 

Sent from my iPhone using Tapatalk

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If you have never updated those x-overs, now is the time. You can send all three to Bob and have them done for about $200. He will replace the caps and test the entire network and let you know if they check out. This way all three will remain the same. I have had Bob do several pair of AA and they all work flawlessly now. I have also done it myself as well to save a few bucks and it is not that difficult but with your other issue, you may want them tested after the update.

You will be glad you did.

There, two cents worth!

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Just now, MookieStl said:

If you have never updated those x-overs, now is the time. You can send all three to Bob and have them done for about $200. He will replace the caps and test the entire network and let you know if they check out. This way all three will remain the same. I have had Bob do several pair of AA and they all work flawlessly now. I have also done it myself as well to save a few bucks and it is not that difficult but with your other issue, you may want them tested after the update.

You will be glad you did.

There, two cents worth!

@MookieStl is one of my mentors and once again has good advice.

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1 minute ago, codewritinfool said:

@MookieStl is one of my mentors and once again has good advice.

Mentor??!!

Thanks Jeffrey  Code!

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13 hours ago, RandyH000 said:

you are right about the possible zener diode going bad    ,  but  you are saying the Square magnet   ferrite K77-EVT35  does not need that  protection  but the Alnicos do -----can you elaborate -please Tx --

 

Mostly.  The K-77/T-35 has a hair-sized lead to the terminal and a power rating of 2W continuous, 20W program and 40W instantaneous.  The K-77-M/T-35A has the same diaphragm as a T-350, with a ribbon lead and a 5/50/100W rating.  *FOR HOME USE* the KLiP diodes may be removed or disabled (unbolt one and let it hang).  For pro or outdoor use, you need them. 

 

When they operate, the tweeter produces a square wave and that sounds hashy, irritating. 

 

Doesn't look like i have the T-350 Cut Sheet on this PC. 

T-35 CS Page 1 of 2.gif

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