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mikepick

Smaller Advent Woofer Distortion

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I am working on a pair of Smaller Advents and one of the woofers has a sort of soft distortion, like a buzz, but not a harsh sort of sound. I'm going to try and add it to the thread as a recording but for the moment I'll just try to describe it.

I bought this woofer from the auction, it was sold with a new surround on it. It looks good, visually, the spider has no irregularities and the cone is intact. The tinsel wire seems solid, and there is no rub from the voice coil when I press it down.

The distortion is more noticeable at low volumes, and it gets masked as you raise the volume. As a background, I've been doing some speaker repair and have replaced surrounds, but am a relative novice.

I pulled the woofer from the cabinet and have done some feeling around with it playing on the workbench, and the one thing that solves the distortion is pressing my fingers lightly on the dust cap. pressing the surround in also stabilizes the sound, but the dust cap had a much more noticeable effect.

Does it seem plausible that the dust cap might need to be removed and re-glued? I don't know how the new surround was attached, I just put a new surround on one of these spit-cap woofer and did not need to remove the dust cap. I may just cut the dust cap out and clean it up to see if it makes a difference, as it seems I have little to lose.

Thanks, Mike

Edit: I am trying to add phots, but it gives me error 200. Visualize a nice looking spit-wad woofer. :)

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Hi, Your  pix should be no larger than 100k. Downsize them and try reloading. Your problem sounds like the "classic" voice coil rub from your description. Removing both the outer surround and the dust cover. Then shimming the voice coil then regluing may fix this. There are several threads with more info out there.

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You are probably right about rub. I just replaced the surround on another woofer, and I pulled it for comparison. In comparison to the problem woofer, the new surround looks more robust and stands a bit taller.

Attached are pictures showing the problem woofer from the top, the spider, and a comparison with the newly fitted surround on the left. (The newer one has a more brown-dish dust cap.)

I don't hear or feel any rub when I push down gently on the dustup on the "bad" woofer, but I do notice a kind of echo—a double tap—when I tap the dust cap gently, which is not present on the good one.

So I think you are right, I will replace the surround since I have a spare, and see if that solves the problem. I did not need to remove the dust cap on the good woofer, and so I'm going to leave it in place while doing the repair.

smaller-advent-spider.jpg

smaller-advent-top.jpg

smaller-advent-compare.jpg

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The glue work on those old woofers was not done very well back when they were made.  Check

them all by applying pressure to lift or move various parts.  The gasket, the dust cap, the spider 

to voice coil joint, everything.

Here is an example on an EPI-100 but the idea is the same:

 

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I had one SA woofer that had been powerfully overdriven, easy to do with 200+W/ch, with the VC former

hitting the back plate and bending.  Here is a thread where I repair it better than new, you might have to

join Audiokarma to see the pictures:

https://audiokarma.org/forums/index.php?threads/small-advent-woofer-repair-some-measurements.819443/

It was easy to remove the cone because the old glue cracks easily pressing down hard on the spider

at the joint.

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Thanks for the info Pete! I've read a bunch of older posts on AK and here about the Smaller Advents, there is not a whole lot of discussion about these and I've read what I can about them since I got hooked on them in the last year.

This will be my second set, I have a set with the green tweeters that I like very much. I'm in the process of cleaning this woofer up for a new surround, hoping it will do the trick. 

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Update: new surround seems to have done the trick, nice clear sound now with none of the prior distortion. The "double tap" effect is no longer present as well, tapping the dust cap lightly produces one hollow sounding thump.

So that worked out, and I'm into the next stage with this set, which is to cover in veneer and add a hardwood nose to the cabinets. It looks pretty good, though it was not without some mishaps, it's not easy to add veneer to an already old and somewhat beat-up cabinet. I stained the veneer with a reddish "gunstock" tone to warm it up and redressed the grill with new linen and a reproduction emblem from the auction site. While I was in there I recapped the crossover as well, figured I might as well.

The partner cabinet, unfortunately, is water damaged, and I was going to try to replace the bottom panel but the damage had cause the bottom sides to swell also. In this case, I'm going to construct my own replica cabinet and see how that works.

 

smaller-advent-cabinet.jpg

smaller-advent-grill.jpg

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Impressive cabinet work - - - looks so much better than new! ;)

Did you strip down to bare cabinets first, and could you describe veneer application? Also, just for posterity, maybe you can cite the cap values found in this pair.

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3 hours ago, ra.ra said:

Impressive cabinet work - - - looks so much better than new! ;)

Did you strip down to bare cabinets first, and could you describe veneer application? Also, just for posterity, maybe you can cite the cap values found in this pair.

Thanks! 🙂Not a super high bar, although I don't know what that vinyl looked like new. It's certainly pretty drab on my sets.

The cabinet work... well it looks good from a distance, though I made a number of unforced errors and so it doesn't quite stand up to a close look. Made a couple of gouges while planing the hardwood nose and sanded through on a corner. The stain color helps blend it all together. 

I used veneer that I got via the big online retailer, which came with a 3M backing adhesive. I did strip the vinyl completely, which wasn't hard, and then gave it a sand as the 3M adhesive likes a smooth surface. I trimmed it with a flush bearing bit and filled the smashed corners with epoxy. Then I miter cut the walnut hardwood nose pieces to size and glued and clamped them on.

You can see a major error here in the photo where the flush trim bit took out an entire edge, it must have curled outward slightly. I had some leftover veneer from the age where I had cut that piece, though, so I cut a new strip and patched it into place. I didn't have enough to use for an entirely new panel.

This set has the soft open-cell foam instead of the fiberglass fill, each cabinet has 5 pieces, 3 behind the tweeter and 2 behind the woofer. I add a little extra poly fill behind the woofer at the bottom to fill the space.

The crossovers in these have two capacitors, Unicon 50V/8mf and 50V/4mf, which I replaced with a pair of Dayton 250V/2uf and a single Dayton 250V/8.2uf. These cabinets came with the red tweeters.

 

smaller-advent-nude.jpg

smaller-advent-veneer.jpg

smaller-advent-edge.jpg

smaller-advent-strip.jpg

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That's a great description, thanks - - including the comments on caps and stuffing, too. Too bad about that one cross grain blow-out - - it's virtually impossible to create any appearance close to "seamless" in that instance with walnut veneer, but it looks pretty good. Looks like your woofer screw holes could use a little reinforcement, too. In any case, these things look so much better with real wood veneer - - maybe only the second time I've seen these speakers improved in this way. Nice work!

This thread may prompt me to post my modified Smaller Advents from last year, which is sort of a poor-man's version (lazy man?) of your project. 

Edit: I've never used that "gunstock" stain but have read about it before, and it really suits my tastes to bring a bit of red hue to the walnut - - - it looks really good on your project.

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On 7/16/2019 at 8:57 AM, ra.ra said:

That's a great description, thanks - - including the comments on caps and stuffing, too. Too bad about that one cross grain blow-out - - it's virtually impossible to create any appearance close to "seamless" in that instance with walnut veneer, but it looks pretty good. Looks like your woofer screw holes could use a little reinforcement, too. In any case, these things look so much better with real wood veneer - - maybe only the second time I've seen these speakers improved in this way. Nice work!

This thread may prompt me to post my modified Smaller Advents from last year, which is sort of a poor-man's version (lazy man?) of your project. 

Edit: I've never used that "gunstock" stain but have read about it before, and it really suits my tastes to bring a bit of red hue to the walnut - - - it looks really good on your project.

I'd be interested in seeing them for sure, I'm obsessed with them right now.

That stain is Varathane brand, to be more precise. The reddish hue was what I was looking for, I had put new veneer on a KLH Model 22 last year and ended up with a bit of a mismatch with its partner, after using a natural Danish Oil to finish. (On the left below).

The blow-out, I think I would avoid in future by being more conscious of where the bearing on the bit is tracing. I was being clever by tracing it lower on certain edges, to avoid smashed edges and corners, but on those edges where the grain meets I think you need to trace as close to the edge as possible. It's easy to sand more oof the corners, but impossible to put it back.

I did end up reinforcing the screw holes as well, I usually put wood glue in them to firm then up and in this case, used epoxy to build it back up again. 

Part two of this project is now ongoing, here is a dry fit of a (hopefully) replica cabinet to replace its partner. Excited to hear how this turns out!

klh-22-pair.jpg

smaller-advent-replica.jpg

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