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DavidR

AR9 and 90 xover question

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Ever since re-capping my AR91s with PP caps I've wanted to do my AR90s.

I have a question on the tweeter crossover difference. The 91 has only a 4uF cap in series with a .2mH coil in parallel and the AR9 and 90 have a 0.105mH coil with a 4uF and 6uF caps in series.

I'm wondering what the 4uF and 6uF in series does. Is the difference only because of the coil difference?

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No, it's not just the coil difference. The 4 and 6 uF caps and .105 mH coil (to ground between them) form a 3rd order electrical slope. The AR 91 xo 4 uF cap and coil forms a 2nd order electrical slope.

Steeper slopes (i.e. higher order) can offer better tweeter protection and reduced harmonic distortion but are more costly and complicated to build.

Edited by Carlspeak
clarificaton of order terms

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Thank you Carl.

Putting caps in series does what to the capacitance (nothing?) and voltage rating(add the two?)?

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Putting caps in series does what to the capacitance (nothing?) and voltage rating(add the two?)?

No! Not nothing. Putting caps in series does a lot and it's not a simple calculation. You can google it, as I did. This page http://www.engineeringtoolbox.com/capacitors-parallel-series-d_1388.html gives the example of a 10uF cap and a 20uF cap. In parallel they equal 30uF as we all know--just add 'em up. But in series they equal 6.7uF.

-Kent

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Thanks for the link Kent.

Very interesting how that works out but it helps me with my decision on what caps to use for caps in that circuit.

Now if I can decide what to do in the bass section. Poly caps will run approx $200 for the pair of speakers and thats just the 350uF.

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I wouldn't bother with film caps for any of the shunt caps that are parallel to the driver in a low pass circuit. NPE's are fine.

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Erse makes a 350uF NPE but its out of stock and they will tell you it is no longer available. However, their parent company, Gabriel Corp, says its a standard item. I'd rather go the single cap route vs paralleling 2 caps. Gabriel also has a 200uF PulseX cap listed as standard but its no longer on the Erse website. No Customer Service tele number for Erse either.

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There is nothing wrong with paralleling caps to the get the value you need. Peter Snell made himself famous doing this on most, if not all of his early designs before his unexpected passing. Here's but one example from a portion of his model A mid and HP section....

post-100237-0-54961600-1428243963_thumb.

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I know there is nothing wrong about it. However, it does lower ESR.

As to NPEs Pete B states that there aren't any NPEs available in the U.S. that are any good (maybe not is exact words); and Roy says many of the ones he's encountered have been running on the high side, some above the given tolerance.

I guess I have to decide if I want to spend the money for PP in the woofer section. I'd like to go that route but that's a good chunk of cash.

Roy talked me into using poly caps in the woofer section of my 91 recap. I'm glad he did. :)

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Actually, paralleling increases ESR. At least that's what I've found wihen testing an ERSE 50 uF NPE vs paralleling two 25 uF ERSE NPE caps. At the same frequency, about 0.2 to 0.3 ohms is added to the two cap arrangement vs one. See WT2 tests below. In the tabular data, ESR is the 3rd column from the right side which is uF.

While I'm not sure how concerned you are about ESR, I concur with Michiganpat's recommendation.

Suggest you look at Madisound's Bennic NPE offerings if you haven't already. Depending on the uF value D.F. can range from 5% max to 10% max. The Bennic 330 uF NPE is $5 and change.

The ERSE caps I have all are printed with 5% tolerance. I did find one that was 10% from the 25 uF target. However, that level of variation was typical in the past and, IMO not nearly as critical in a BASS circuit than in a mid or HP circuit.

post-100237-0-31735900-1428251781_thumb.

post-100237-0-84150600-1428251810_thumb.

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I know there is nothing wrong about it. However, it does lower ESR.

As to NPEs Pete B states that there aren't any NPEs available in the U.S. that are any good (maybe not is exact words); and Roy says many of the ones he's encountered have been running on the high side, some above the given tolerance.

I guess I have to decide if I want to spend the money for PP in the woofer section. I'd like to go that route but that's a good chunk of cash.

David,

What makes you think a single modern 350uf cap will have the same esr as the original? I have found larger value "modern"/inexpensive npe caps to stray further from stated capacitance value than smaller caps. In fact, it is possible your original cap will measure closer to stated value than a new npe. Do you have a cap meter with which to do some basic measurements?

Getting capacitance right is more important than speculating about esr.

Roy

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Actually, paralleling increases ESR. At least that's what I've found wihen testing an ERSE 50 uF NPE vs paralleling two 25 uF ERSE NPE caps. At the same frequency, about 0.2 to 0.3 ohms is added to the two cap arrangement vs one. See WT2 tests below. In the tabular data, ESR is the 3rd column from the right side which is uF.

While I'm not sure how concerned you are about ESR, I concur with Michiganpat's recommendation.

Suggest you look at Madisound's Bennic NPE offerings if you haven't already. Depending on the uF value D.F. can range from 5% max to 10% max. The Bennic 330 uF NPE is $5 and change.

The ERSE caps I have all are printed with 5% tolerance. I did find one that was 10% from the 25 uF target. However, that level of variation was typical in the past and, IMO not nearly as critical in a BASS circuit than in a mid or HP circuit.

Carl,

That's an interesting finding regarding esr. Paralled resistance should decrease. Could it be the leads? Most cheap, modern npe's don't use copper leads. Whatever the case may be I don't think it is a significant consideration when replacing caps, and agree with you regarding the use of paralleled caps to achieve desired values.

I have not found significant differences between Bennic, Parts Express, or Erse npe's. I know resident cap guru John O'Hanlon has a rather low opinion of all of these inexpensive npe's. Given the initial high quality of the original caps found in AR speakers, he believes AR would have used all film caps if they were manufactured today.

Roy

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Carl,

That's an interesting finding regarding esr. Paralled resistance should decrease. Could it be the leads? Most cheap, modern npe's don't use copper leads. Whatever the case may be I don't think it is a significant consideration when replacing caps, and agree with you regarding the use of paralleled caps to achieve desired values.

I have not found significant differences between Bennic, Parts Express, or Erse npe's. I know resident cap guru John O'Hanlon has a rather low opinion of all of these inexpensive npe's. Given the initial high quality of the original caps found in AR speakers, he believes AR would have used all film caps if they were manufactured today.

Roy

my plan for the AR58's I picked up was to re-cap, polys for the high pass series caps, bennic NPE's for the large paralleled caps in the low pass sections....not sure if I can find a capacitance meter to test the old ones...would you not replace the larger caps?

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David,

What makes you think a single modern 350uf cap will have the same esr as the original? I have found larger value "modern"/inexpensive npe caps to stray further from stated capacitance value than smaller caps. In fact, it is possible your original cap will measure closer to stated value than a new npe. Do you have a cap meter with which to do some basic measurements?

Getting capacitance right is more important than speculating about esr.

Roy

Roy,

I do not think or make believe I know about modern NPEs and their ESR. That's why I ask these silly questions of people like you and read threads by all of you knowledgeable members.

I do have a capacitance meter. (one of the 24uF Callins caps in the 91s measured 40.4uF)

I will be opening up the 90s in the near future and will know more then.

Carl, very interesting info on ESR. I've read lots of your posts on caps and find the measurements you post to be very helpful in understanding this stuff.

I've looked at the Bennics on Madisound and the Parts Express NPEs (the P.E. brand may be made by Solen as they own Dayton).

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my plan for the AR58's I picked up was to re-cap, polys for the high pass series caps, bennic NPE's for the large paralleled caps in the low pass sections....not sure if I can find a capacitance meter to test the old ones...would you not replace the larger caps?

I personally would not replace the larger caps unless I was sure there was something wrong with them. I recently measured the caps on several "parted out" AR-9 crossover boards and found the larger caps to measure quite well...better than any combination of modern npe's I had on hand with regard to capacitance. Several of the lower value caps, however, did not measure as well, with a couple of them being significantly out of spec.

Roy

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Roy,

I do not think or make believe I know about modern NPEs and their ESR. That's why I ask these silly questions of people like you.

David,

Your statements such as "I know there is nothing wrong about it. However, it does lower ESR" and that you would "rather" go with a single cap vs paralleled caps suggested otherwise. I've seen you post the same type of questions in the AK forum, which is a recipe for confusion if there ever was one. :) To be fair, I'm not convinced there are valid answers to some of the concerns I've seen you post about.

Two professionals whose opinions I respect a great deal actually have different opinions on this topic. John O'Hanlon, who has done extensive work with capacitors recommends using all film caps as replacements (with, perhaps, some added series resistance) due to the low quality of typical modern npe's, and Ken Kantor, design expert of NHT fame, says to just use modern npe's in the old beasts and be done with it...but only if you can prove there is something wrong with the original caps. Some hobbyists will use mylar (polyester) caps to retain some esr, and still have the reliability and consistency of film caps (I'm in this camp...but again I'm only speculating as to the actual advantages of doing so).

Btw, since you have a meter, you can measure two caps in series to demonstrate the answer to the question you had on that subject.

Roy

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I personally would not replace the larger caps unless I was sure there was something wrong with them. I recently measured the caps on several "parted out" AR-9 crossover boards and found the larger caps to measure quite well...better than any combination of modern npe's I had on hand with regard to capacitance. Several of the lower value caps, however, did not measure as well, with a couple of them being significantly out of spec.

Roy

Roy,

I completely understand "if it ain't broke don't fix it" especially if the modern NPEs are not up to the quality of older ones. BUT I thought the whole reason for replacing old caps is that NPEs have a finite life expectancy. One would expect a 50-year-old cap to be off (like David's Callins example) but if it's not, can one reasonably expect it to last another 50 years? My assumption has been that an old electrolytic, even if it's within spec, is on borrowed time. Is that incorrect?

-Kent

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Roy,

I completely understand "if it ain't broke don't fix it" especially if the modern NPEs are not up to the quality of older ones. BUT I thought the whole reason for replacing old caps is that NPEs have a finite life expectancy. One would expect a 50-year-old cap to be off (like David's Callins example) but if it's not, can one reasonably expect it to last another 50 years? My assumption has been that an old electrolytic, even if it's within spec, is on borrowed time. Is that incorrect?

-Kent

Hi Kent,

That has been the general opinion in audio forums, but John O'Hanlon's evaluation of AR's better caps and Ken Kantor's comments suggest otherwise. Some npe caps are simply better than others, and typical modern npe's (including Bennic) do not always measure as well as some of the old ones. So the question becomes, is it better to use new questionable npe caps, or leave in those that at least measure acceptably with a basic meter? The alternatives are to use all film caps or a parallel mix of npe's and film caps.

....on a lighter note...Who among us is expecting to be listening to these things 50 years from now? :)

I don't know the answer, which is why I (like you) use inexpensive film caps whenever possible...and I measure everything!

As an aside, Larry/Vintage AR (who is an electrical engineer, and is not a person to "overspend" on anything) will only use film caps as replacements, and leaves the larger original npe's in place if they measure well.

Roy

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Roy,

You may be reading into something that isn't there. I'm not trying to pick a fight or be confusing. I've done so much reading on the subject and have found statements from knowledgeable people that are totally opposite or certainly different. It is confusing. I've even read opposite responses from a knowledgeable person saying one thing here and something else over there. So if I'm sounding or coming across as confusing its probably because I am. Would I rather not parallel caps? I would rather not. I have no electrical reason or logical reason for it other than invalid things like: 2 caps cost more, its more work, room to install is more difficult.

I can tell you that I value each and every members comments and knowledge and have used that info and it yielded results I like. Both you and Carl have offered me some much of your knowledge and I am totally appreciative of that.

I have paralleled caps in some small 3-way Yamaha speakers I use in the garage and basement. I used the polys and mylars Kent told me about from Madisound. The speakers sound very good for what they are but I'm unable to compare them to the original design as I replaced the mids and tweeters and the xover is totally different now.

As to testing 2 caps in series: I hadn't even thought of doing that. Duh. The math to calculate it is not difficult.

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One should also note that you can get better tolerance caps quite easily by paralleling caps. If you aim to make two 150UF caps.... buy 2 pc 70UF caps and 2pc 80UF caps. Measure caps and bundle lowest reading 70UF and highest reading 80UF cap to make the first cap, highest reading 70UF and lowest reading 80UF will make the second cap... basically this way you will end to less than 3% tolerance when caps do have 5% factory tolerance.

Best Regards

Kimmo

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One should also note that you can get better tolerance caps quite easily by paralleling caps. If you aim to make two 150UF caps.... buy 2 pc 70UF caps and 2pc 80UF caps. Measure caps and bundle lowest reading 70UF and highest reading 80UF cap to make the first cap, highest reading 70UF and lowest reading 80UF will make the second cap... basically this way you will end to less than 3% tolerance when caps do have 5% factory tolerance.

Best Regards

Kimmo

That’s exactly what I did with the surplus caps from Madisound. I bought 10 each of the 10uF poly and 2uF mylar. I mixed and matched to get pairs that were the same.

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I do have a capacitance meter. (one of the 24uF Callins caps in the 91s measured 40.4uF)

Those black Callin's caps with the red ends are some of the worse caps I've measured. They are a fine example of my 'bad and the ugly' ones.

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Carl, The 24uF has a metal case. But yes, the black ones with red ends are the pits. I attached a chart of the before/after values.

I really liked that thread, BTW.

What are those black/red ones made of? I think I read they were some type of pvc. Also, what's a safe disposal method for the caps from the 91s?

AR91 cap values.pdf

post-149980-0-82603200-1428366519_thumb.

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I personally would not replace the larger caps unless I was sure there was something wrong with them. I recently measured the caps on several "parted out" AR-9 crossover boards and found the larger caps to measure quite well...better than any combination of modern npe's I had on hand with regard to capacitance. Several of the lower value caps, however, did not measure as well, with a couple of them being significantly out of spec.

Roy

thanks for the feedback....I'll see if we have a capacitance meter here at work. I have to remove at least 1 leg from the circuit to measure, correct?

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I'll see if we have a capacitance meter here at work.

FWIW, a capacitance meter is a very useful tool to have on hand. I have a cheap Chinese LCR (inductance, capacitance, resistance) meter I got on ebay for under 20 bucks, including test leads and shipping, and it's my understanding they are just as accurate as the high-priced ones.

If you only want to check capacitance, there are some capacitance meters on the bay for 13 bucks.

-Kent

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