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Type AA crossover rectangular capacitor replacement


Tizman
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Tizman- if you do end up replacing the capacitors please message me as I would like your old ones as spares for my original crossovers. I like the Aerovox caps. The 13uF is an odd value to find today so I wouldn't mind some spares if mine go south. At the very least I will spend the time to see if they are worth keeping as backups instead of just blindly throwing them in the trash.

 

 

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Thanks for all the replies.  I’m going to replace all the caps, check for the brass screw and keep the rest for now.  I have a bunch of Solen caps in the correct values, including 13uF, taken from a stack of three way crossovers I bought from a theatre redo.  I also have a bunch of inductors including 16 gauge 2.4mH ones.  Would these be close enough to replace the 2.5mH ones in the AA?  

C63666D3-DA53-4DE7-BF8C-0107AA3ACA04.jpeg

661F3036-588F-41A8-8917-F6642F670C32.jpeg

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9 minutes ago, captainbeefheart said:

Tizman- if you do end up replacing the capacitors please message me as I would like your old ones as spares for my original crossovers. I like the Aerovox caps. The 13uF is an odd value to find today so I wouldn't mind some spares if mine go south. At the very least I will spend the time to see if they are worth keeping as backups instead of just blindly throwing them in the trash.

 

 

I’m going to keep the original caps so I can return the crossover to original for any future sale.  I will let you know if I change my mind though.

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Check the DCR of that air core inductor and compare it to the stock inductor, I highly doubt you are bringing the stock one into core saturation which is the only benefit of having an air core inductor, no core interaction. The air core will add resistance into the woofer circuit lowering your damping factor and increasing the loss across it. They make super core inductors with extremely low DC resistance that won't saturate the core, I would choose those over an air core any day of the week.

 

 

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5 hours ago, Dave A said:

I use a B&K 885 set to 1000hz. I bought this one because it was the same one Bob Crites used for cap measurements. Of course he also could measure the output of the whole crossover with other equipment which I do not have. I figure I am not guessing with poor equipment at what is going on. If I want I can also measure inductance accurately and resistance also. While I may not be able to judge  the aggregate of a whole crossover at once I can assess each component and if the values are correct I make the assumption the crossover is correct or at least according to OEM schematic specs correct.

 

 In any case back to the idea of recapping there is no doubt in my mind and practical experience there is a real benefit for the OP to recqp.

 

1000Hz is much better for testing the 13uF capacitor, at least that is in the region of useful frequencies to test at. For the 2uF you want to test ESR between 5kHz and 20kHz.

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5 minutes ago, Tizman said:

Thanks for all the replies.  I’m going to replace all the caps, check for the brass screw and keep the rest for now.  I have a bunch of Solen caps in the correct values, including 13uF, taken from a stack of three way crossovers I bought from a theatre redo.  I also have a bunch of inductors including 16 gauge 2.4mH ones.  Would these be close enough to replace the 2.5mH ones in the AA?  

C63666D3-DA53-4DE7-BF8C-0107AA3ACA04.jpeg

661F3036-588F-41A8-8917-F6642F670C32.jpeg

why even bother messing  with the old board , it may have a Collector Value on the Garage Sale , you can build a new crossover on a wood  board using the parts you have -

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11 minutes ago, captainbeefheart said:

Check the DCR of that air core inductor and compare it to the stock inductor, I highly doubt you are bringing the stock one into core saturation which is the only benefit of having an air core inductor, no core interaction. The air core will add resistance into the woofer circuit lowering your damping factor and increasing the loss across it. They make super core inductors with extremely low DC resistance that won't saturate the core, I would choose those over an air core any day of the week.

 

 

I checked the resistance across the 2.4mH inductor with a DMM set to resistance, and it is 1 Ohm.  It is reasonably beefy. 

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5 minutes ago, Tizman said:

I checked the resistance across the 2.4mH inductor with a DMM set to resistance, and it is 1 Ohm.  It is reasonable beefy. 

 

That is double what my 2.5mH inductor measures in my LaScala AA network, I just measured .5 ohms. So the air core you have will add some resistance and reduce your damping factor for less speaker control. I don't think it is worth it personally but try both and see what you like.

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7 minutes ago, RandyH said:

why even bother messing  with the old board , it may have a Collector Value on the Garage Sale , you can build a new crossover on a wood  board using the parts you have -

 

I agree about keeping the old boards original an build some new boards. Someone like myself would prefer the old crossover network if purchasing the Khorns from you.

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12 minutes ago, Tizman said:

I also have several .51mH air come inductors that I could parallel to get a .255mH value.  Is that close enough for replacing the .245mH value in the schematic?

 

You would have to place them in series to get the inductance you want, they are the reciprocal of a capacitor remember. You would have to measure/calculate the DCR of them all in series to get an idea if it's worth it.

 

Here is my XO, my meter reads .4 ohms and that is with the cheapo long test probe cables which most likely add .1 to the total, so in actuality the stock core inductor is more like .3 ohms.

 

 

xo.jpg

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1 hour ago, jimjimbo said:

Dave, isn't it great how posts can be edited/manipulated to fit the level of misinformation that is so prevalent here?  Yea, WOW is right.

Yeah I am not certain what is gained by doing that. Debating ideas is fine but rewrites changing what was actually said is not.

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For anyone curious what the filters should look like at each output here you go.

 

I used the drivers DCR as a resistive load, when I take them out of the speaker this is how I test them with a load.

 

There are free signal analyzers for your computer, all you need is a decent sound card and make sure you do not input too much signal into the sound card. You can easily sweep these crossovers with just a 2v input and all the outputs will be safe for your sound card. During testing take screenshots of the tests then compare against the simulation. The order of pictures follows the schematic; 1) woofer 2) mid 3) tweeter

 

 

schem.png

woof.png

mid.png

tweet.png

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1 hour ago, captainbeefheart said:

 

You would have to place them in series to get the inductance you want, they are the reciprocal of a capacitor remember. You would have to measure/calculate the DCR of them all in series to get an idea if it's worth it.

 

Here is my XO, my meter reads .4 ohms and that is with the cheapo long test probe cables which most likely add .1 to the total, so in actuality the stock core inductor is more like .3 ohms.

 

 

xo.jpg

I am using extra long probes that add .2 Ohms or so, so I’m probably actually at .8 Ohms.  That is .5 Ohm above the stock inductor.  The other associated issue with the extra .5 Ohms is that I use mostly single ended triode connected tube amps, which have a high output impedance.  Perhaps not a great idea.  I’m not too concerned about the losses created by the additional .5 Ohms, as the Klipschorns in my room are a bit bass heavy, but the decreased damping might be an issue.  I’ll try both and see.

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2 hours ago, Tizman said:

 I also have a bunch of inductors including 16 gauge 2.4mH ones.  Would these be close enough to replace the 2.5mH ones in the AA?  

 

 

Would be close enough in my world. AA's are 1st order crossovers where values are not that critical. I noticed that CBHeart wants your old square caps. Technicians know film caps in crossover networks, and for that matter old electronic gear, rarely just fail and hold their values pretty good. Not a hard working electronic piece in a crossover network. Unless they are leaking probably still good. That being said they are sure ugly and I would probably replace just because. I restore old equipment and just replace the electrolytics and leave the films alone unless they are known to fail such as really old tube electronics. The theory being destroying the old sound many enjoy. I really do not know any restorer of old equipment either in person or online sources that replace film caps in old equipment. I cannot see why crossover networks would be any different except from those trying to sell such. It is a crap shoot if replacing caps will be an improvement. Many claim too bright after doing so. 

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24 minutes ago, Tizman said:

John A has posted that including a .35 to .4mH inductor between the T2A and the squawker helps to take out a hump in the K-77 squawker’s response at 9K Hertz.  Is this something I should include?  

 

Take a look at the third picture down of the tweeter frequency response I posted 4 posts ago, you can easily see this bump at 9kHz. I can simulate whatever you want to try so you can see what will happen. I will add an inductor into the simulation where you suggest to see what happens.

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