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Small Advent Crossover Variation and questions


redpackman

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I am in the process of restoring a pair of Small Advents. I opened them up today and found the crossover has a 12uf and an 8 uf cap along with a 1ohm 5w resistor.

As near as I can tell the diagram of the crossover is like the attached diagram EXCEPT that the cap between the 4 ohm (+) terminal and the place where the other 8 uf cap and resistor join is a 12 uf cap and not an 8 uf cap as diagrammed and the resistor is a 1 ohm and not a 3 ohm as listed. Put another way working from the 4 ohm terminal the first capacitor one would reach in the chain would be a 12 uf cap, [ then an 8 uf and 1 ohm 5 watt resistor in parallel.]

Some report 5 uf caps, others report 2 8uf caps. Then others say they have........ :wacko:

I have read elsewhere that the best cross over is the one that "sounds the best." I haven't the time or the sonic memory to try out all the variations. Is there one that Advent seemed to "settle on" or do they simply have about a dozen variations for the crossover for their Small Advent speaker and we're to just guess at which is "best" and hope it works out.

Suggestions from the experts?

Smaller_Advent_Crossover.pdf

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Which tweeters do your Smaller Advents have? The green ones or the orange ones?

The original green ones had a smaller magnet than the full sized Advents had to match the efficiency of the woofer. Later, Advent put tweeters in that had the large magnets in them and the cones are orange (although there may be some with green cones). The thing to do is actually look at the magnets. The smaller ones are 2.5 inches square and the larger ones are 3 inches square.

I believe Advent changed the crossover when they made the change sometime in 1975. It makes sense that the crossover you have would have been used in the smaller magnet units and the crossover with the 3 ohm resistor in the later, large magnet units.

Doug

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Thank you. That is a help. BTW the caps tested out at 8.1 uf for the 8 uf cap and 12.45 uf for the 12 uf cap. I assume they are therefore still serviceable?

I also checked the tweets. They had September 1973 stamped on them and they were the smaller 2.xx size. Thanks again for the info.

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I agree with Roy. These days, there seems to be almost a religion about automatically replacing capacitors in the belief they are automatically bad after x number of years.

Although there are perfectly valid reasons for that (the electrolyte drying out, etc.), I just think it's better to leave them alone if they still are in spec. Of course, ideally, you would want to check the series resistance also but every time I have, they seem to be OK in that regard too.

And, even more of a religion seems to be to replace the original style of capacitors with some other types, even exotic types, in the belief that these different types of capacitors will automatically improve the sound of the speakers. This all without considering the speakers were possibly voiced with the types originally included and using others may affect the sound of the speakers but maybe not in a positive way.

I say all the above in spite of my belief, through experimentation over the years, that there really isn't that much difference in sound between different capacitor types.

I just think it's better to leave them alone if they are working and the speakers sound good. All five pairs of my original Advents have their original capacitors and they all sound alike and all sound wonderful.

Doug

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  • 3 months later...

I agree with Roy. These days, there seems to be almost a religion about automatically replacing capacitors in the belief they are automatically bad after x number of years...

Doug

I agree wholeheartedly. Recap fever is epidemic. Like the tech at McIntosh told me when I asked if they recap older units that come in for repair, "We don't replace parts that aren't broken." I refoamed a pair of Smaller Advents this morning and the caps tested and sound perfect after 40 years.

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  • 4 years later...
On 8/18/2013 at 7:14 PM, RoyC said:

Red,

The last pair of Smaller Advents I opened up had original green tweeters and your crossover, which would be consistent with Doug's comments.

Roy

I finally have a pair with green tweeters and also have 12uF to 1 ohm/5W resistor with 8uF across it,

 a light blue dot type inductor to ground (across the tweeter) is  .36 mH/1.1ohm DCR.

The green 2.5" square (small) magnet tweeter is 3.2 ohms DCR.

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  • 4 months later...

Something odd, I finally opened the second Small Advent in this pair and the 

inductor has a yellow dot and measures .056 mH .30 R.  I'd guess that they dot

color is a code for value but not sure, so it was either fabricated incorrectly or

the coil overheated and has shorted windings.

I might just unwind both of these since I have no use for them.

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  • 1 year later...

Hi,


Just to add to the cap question.  I just picked up an original unmolested pair of 1975 Smaller Advents.  The crossovers have not been touched.  The caps had the original hot glue and were the same brand.  No work had been done on these crossovers.  The values were: 8uF, 5uF and 3 ohm.  I replaced with exact values in Solen.

Anyone else have 8uF and 5uF?

 

Thanks

 

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On 10/25/2019 at 2:30 PM, Eabos1 said:

The values were: 8uF, 5uF and 3 ohm...

Hi Eabos, and welcome to the Advent forum. I know I've never seen a 5uF cap used in a Smaller Advent crossover, but I think they were at least three known variations for this circuitry. Can you post a pic of the original crossover (or the removed caps)? And also, do your tweeters have red or green fronts, and what is dimension of tweeter magnet? Did your Solen re-cap result in any perceptible improvements?

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  • 1 month later...

After Advent started putting tweeters with the large magnet in the Smaller Advent, they may have been trying to zero in on the perfect values of capacitors and 1975 is when they made the magnet size change. It's kind of like when they were settling on the values for the original Advents. In any event, the 3 ohm resistor indicates the tweeters will have the large magnet. It was needed to tone down the tweeter a bit to match the woofer efficiency. The original Smaller Advent did that with the smaller magnet and only needed the 1 ohm resistor.

Doug

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  • 1 year later...

Found this old thread through Google -- trying to get some info on the Smaller Advents I just got.

The Smaller apparently weren't a matched set.

One (SN #214xxx) has the later yellow foam, an orange fried egg tweeter, and a crossover with 8uF and a 4uF caps - very standard

The other is earlier - (SN #184xxx - date stamp May 6 1975), and it has the same orange tweeter, but with pink fiberglass fill, and the crossover has 8uF and 5uF caps - which I have not seen referenced anywhere else. The crossover & caps are clearly original, so it isn't a matter of a mismatch by a PO.

I had only opened the first one before ordering the caps, so I have two sets of Dayton Precision 8.2uF and 4uF enroute -- rookie mistake!

Any thoughts on the 5uF cap? I guess replacing it with a 4uF to match the other speaker is not a sound move? Or would it actually make them blend better? The crossover design looks pretty similar. Should I just get a 5uF cap (a big PITA since the order is on the way...)

Open to suggestions!

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Using a 4uF capacitor instead of the original 5uF won't hurt anything. You probably won't really hear a difference. It had more to do with Advent's measurements to zero them in.

However, if you want to maintain the speaker with original values and can't find a 5uF capacitor, put a 4uF and 1uF in parallel.

Doug

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On 6/16/2021 at 9:52 PM, Doug G. said:

Using a 4uF capacitor instead of the original 5uF won't hurt anything. You probably won't really hear a difference. It had more to do with Advent's measurements to zero them in.

However, if you want to maintain the speaker with original values and can't find a 5uF capacitor, put a 4uF and 1uF in parallel.

Doug

Thanks for the reply -- I'm going to try it with the 4uF -- I expect my ears won't detect the difference, and I can alway redo it if so.

 

 

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I forgot to mention, too, that the drivers, assuming they both have large magnet tweeters, are the same and will be expected to perform the same with the same crossover components. It's not like they were matching the crossover components to individual drivers or anything like that.

Doug

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