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AA Crossover refresh?


alzinski

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On 7/3/2017 at 4:56 PM, djk said:

" I thought the whole reason you changed them was due to age. "

 

The Russian caps are hermetically sealed, the oil caps used by Klipsch after the early '70s were not. Lead failure due to ESR on non-hermetic caps is the issue, age, per se, is not.

Thanks.

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On 7/4/2017 at 3:14 AM, Deang said:

People. Don't forget - if you're strapped for cash - please pursue battery biased (charge coupled) crossovers. You can use Daytons or Bennics and they sound great. 

 

I have asked folks about this in the past and not one can give me a half decent explanation. I can maybe see doing this with bipolar electrolytic caps (why anyone would use them to begin with is beyond me) but why would you do this with a film cap? I will try and dig an old email out for when I asked a chemist that I believe that worked in the capacitor industry, from memory I believe he laughed at the notion.

 

 

 

I still plan to set something up to measure the ESR of the original caps. I will post the results for anyone interested.

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I ordered some of the Russian MBGO paper in oil caps from the seller on e b a y.  I ordered (6) that are "matched" at 2.06uf each and (2) 10uf that are a matched pair at 10.9uf. The 10's with a pair of 2's will give he the 13uf rating for the mid.  For $37 shipped, it's no sweat off my brow to give them a listen and see what they do.  

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why should one choose type A vs type AA crossovers? I've only heard the latter and my understanding is that it was built to help protect tweeters from melting at high volumes. What sonic differences exist? Is the type A suitable for La Scalas which are used for both music and HT? Especially in the context of using CT-120 and A55-G drivers.

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My "Belle clones" will be using CT120's and K-55's and I've read the tweeter protection is less needed, too.  Not that I'm playing at crazy levels but also not using K-77's.  Might go to A-55's later.

 

The A and AA look identical except for a steeper slope crossover for the tweeter and the protection circuit.  But there's more to it of course.

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1 hour ago, Thaddeus Smith said:

I've only heard the latter and my understanding is that it was built to help protect tweeters from melting at high volumes.

There has to be more difference than that.  I'd wager that the AA is more than an A with a zener diode.

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1 hour ago, avguytx said:

My "Belle clones" will be using CT120's and K-55's and I've read the tweeter protection is less needed, too.  Not that I'm playing at crazy levels but also not using K-77's.  Might go to A-55's later.

 

The A and AA look identical except for a steeper slope crossover for the tweeter and the protection circuit.  But there's more to it of course.

I've got k-77's and k-55-m's if you need something to get started with...

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I appreciate that. I've already got new K-33's, k501/K55's (not new), CT120's, and the Type AA's (need rebuilt). Also have the complete top grill section with cloth where the mid amd tweeter go. Just got to start the build. 

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On 7/5/2017 at 11:43 AM, alzinski said:

 

I have asked folks about this in the past and not one can give me a half decent explanation. I can maybe see doing this with bipolar electrolytic caps (why anyone would use them to begin with is beyond me) but why would you do this with a film cap? I will try and dig an old email out for when I asked a chemist that I believe that worked in the capacitor industry, from memory I believe he laughed at the notion.

 

I still plan to set something up to measure the ESR of the original caps. I will post the results for anyone interested.

 

ESR of original capacitors have been posted here many times - all measure horrible. 

 

I'm sure your chemist is a genius who has never listened to a charge coupled network. 

 

http://www.audioheritage.org/vbulletin/showthread.php?18909-Charge-Coupled-Crossover&s=69332e152dcfe68ae9187065f5498d26

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On 7/5/2017 at 8:45 PM, avguytx said:

I appreciate that. I've already got new K-33's, k501/K55's (not new), CT120's, and the Type AA's (need rebuilt). Also have the complete top grill section with cloth where the mid amd tweeter go. Just got to start the build. 

 

I use the Type A. It sounds better at the volumes I listen at (not "loud"). I rarely hit peaks of 90dB. I sit pretty close, which also needs to be factored in. Movies get more volume, and I have no complaints on that front either - it sounds great. 

 

The AA doesn't deliver as much power to the tweeter, so it doesn't sound as crisp at the top, which makes it a bit more forgiving when you push the loudspeaker.

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Is that because of the protection circuit that limits it or from the added parts and how they're set up?  I'm not a crazy loud listener these days but I do have my moments when my wife and kids are gone that I may hit 100db+ peaks.  Kind of overrides my tinnitus for awhile.  ha  

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On 7/5/2017 at 11:43 AM, alzinski said:

 

I have asked folks about this in the past and not one can give me a half decent explanation. I can maybe see doing this with bipolar electrolytic caps (why anyone would use them to begin with is beyond me) but why would you do this with a film cap? I will try and dig an old email out for when I asked a chemist that I believe that worked in the capacitor industry, from memory I believe he laughed at the notion.

 

 

 

I still plan to set something up to measure the ESR of the original caps. I will post the results for anyone interested.

If you (or anyone else) is interested in acquiring original caps from 2uf up to 30uf, let me know, I've got a box full of them.

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5 hours ago, avguytx said:

Is that because of the protection circuit that limits it or from the added parts and how they're set up?  I'm not a crazy loud listener these days but I do have my moments when my wife and kids are gone that I may hit 100db+ peaks.  Kind of overrides my tinnitus for awhile.  ha  

 

The zener diodes don't do much unless you're listening at absurd levels. I've built over 300 pairs of AAs without the tweeter protection, and I've never had one person lose a tweeter - ever. Tweeters were mostly being lost to turn on transients, which had more to do with issues related to early solid state design, than excessive power.

 

The ALK Universal also doesn't provide tweeter protection -- where are the failures (non-existent).

 

If you have tinnitus, use the Type A and watch your volume levels. Get used to listening at reasonable volume levels, because listening loud is robbing you of your hearing.  

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It wouldn't surprise that the ESR has increased which is why I want to change the caps out.

 

 

As for the "charge coupled network", IF people are actually hearing a difference could it not be attributed to the two caps being put in series effectively increasing the ESR? From what I have read the battery bias is supposedly for getting rid of "crossover distortion". Stuart Yaniger couldn't measure any crossover distortion and so far in all my searching is the only person that has actually done any sort of testing. Here is the link: http://www.diyaudio.com/forums/multi-way/124824-electrolytics-sound-fine-post1543205.html#post1543205

 

If the battery bias trick actually does anything it should be measurable, and if anyone has any links they can share to actual measurements then I am going to assume it's a placebo effect, same as people saying they can hear differences with exotic speaker cables, interconnects, and power cables. Especially if you guys are doing this to film caps its a bit ridiculous.

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10 hours ago, alzinski said:

If the battery bias trick actually does anything it should be measurable, and if anyone has any links they can share to actual measurements then I am going to assume it's a placebo effect, same as people saying they can hear differences with exotic speaker cables, interconnects, and power cables. Especially if you guys are doing this to film caps its a bit ridiculous.

 

I've not measured but I think the physics is based on keeping the dielectric films in the capacitors charged to avoid soak back.  I'm sure a SPICE geek could demonstrate that a bias voltage across the reactive elements of the standard capacitor model mitigates DA effects.

 

 

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1 hour ago, John Warren said:

 

 

I've not measured but I think the physics is based on keeping the dielectric films in the capacitors charged to avoid soak back.  I'm sure a SPICE geek could demonstrate that a bias voltage across the reactive elements of the standard capacitor model mitigates DA effects.

 

 

 

 

This pill I can swallow much more than the crossover distortion argument, I originally said I can sort of see doing it with certain dielectrics like aluminum electrolytics (these do have high DA). Teflon and PP caps have an extremely low DA and I would think being in a low Q circuit would dampen any artifacts, basically there is a low impedance path to earth through the voice coils of the squawker and tweeter. 12uF isn't a large value and most of us can spring for a decent cap at this value, when large value caps are needed >40uF I can see the use of certain dielectrics with poor DA and then battery bias could be worth it. For now I feel comfortable using a good film cap (possibly a motor run) for doing my cap refresh in my AA networks without any batteries. I am also toying with surplus military caps from Russia.

 

Does anyone know the ESR range of the original caps that were used when they were new?

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The DIY thread was interesting, though I sure can't claim to have understood all of it!

 

My point is simply this: If you compare a metalized type to a true film type, they don't sound the same. If you apply DC bias to the metalized caps, they begin to sound more like true film types -- why is that?

 

Are we to believe that adding a 9v battery into the circuit does nothing? Really? Since when does circuit modification ever result in a null response? I mean, it's doing SOMETHING.

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