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ra.ra

Prototype or DIY?

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Am just posting this mostly as a curiosity, but of course, seeking comments, questions, and suggestions as well. This pair of mini-speakers (6.25" x 9.25" x 6") was found at a weekend flea market - - the seller was a guy who is very knowledgeable and lives just down the road from where Roy Allison had his company in Natick, MA; also, seller was involved somehow in the liquidation of the estate of Victor Campos in Framingham, MA. Some months ago I posted in the Allison forum about an Allison equalizer (The Electronic Subwoofer) which was being sold by the same seller, and that piece of gear also involved Roy and Victor.

This pair of speakers is some kind of one-off experiment - - perhaps even a prototype? - - and appears to fit somewhere within the typology of a Realistic Minimus 7 or 11 or 12; or perhaps an ADS 200c or 300c. These were packed nicely in a box-to-fit with address label (postmark date is October 2003), and were wrapped in several bands of clear packing tape (?). No rear wiring terminals - - just separate pairs of tweeter and woofer wires extending thru rear panel. The speakers are heavy - - cabinets are fabricated from nominal 1/2" high quality MDF with neat miter and dado joints. Upon initial test, one speaker is working; the other is mute.

That's all I know so far. More info once I poke around inside.

box closed.jpg

box open.jpg

address label.jpg

rear wires.jpg

tape.jpg

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Taking these apart revealed the components - - nothing particularly unusual here, but the first glance at the backside of this woofer made me think there was some mad scientist at work here - - what's this double magnet thingy? It was soon determined this speaker was not functioning because: a) the coil wire had become detached from woofer terminal; and b) the tweeter magnet had completely separated from VC, dome, and face plate.

The drivers each look familiar but have no ID marks except the woofer, which has a date sticker from August 2002. The tweeter has a 3 ohm resistor in series with a 4.7uF cap, and the woofer has a 0.90mH coil (one is .040 + 0.50 and the other is 0.70 + 0.20).

Other pics show cabs patched and sanded, and comparison with similar speaker models for reference. Shown L to R: Realistic Minimus-11, topic speaker, ADS 300, Minimus-7.    

magnets.jpg

tweeter rear.jpg

woofer rear.jpg

cabs sanded.jpg

speaker line-up.jpg

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Here's where I need some help. The tweeter VC has continuity and DCR measures at 6.2 ohms (similar to the other) but I'm not sure how best to re-assemble the parts. How to ensure proper alignment? What is the sequence of steps? Any special tools required? What type of adhesives?

tweeter innards.jpg

tweeter VC.jpg

tweeter magnet.jpg

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If it's Roy Allison wouldn't DIY and prototype be pretty much the same thing...?

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45 minutes ago, genek said:

If it's Roy Allison....

I can only go so far in vouching for their provenance, but thanks for your help.

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The magnet of the unmounted tweeter was probably glued to the back of the woofer magnet at one time . I have seen this arrangement to cause less interference  to the old tv or computer screen. The so-called bucking magnet also increase the magnetic strength of the woofer lowering the Qe.  But I am only guessing. 

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6 hours ago, ra.ra said:

I can only go so far in vouching for their provenance...

.....oops, I was running out the door earlier and didn't mean to sound so curt.

Many members here aren't much interested in small speakers, and these don't necessarily even belong in this forum, but I have great respect for the cumulative knowledge and opinions of the CSP membership. Re: these speakers, you can see clearly what I've found, what I've learned, and what I've uncovered - - - and now... where I need advice. There is quite possibly an interesting backstory behind these, but I have no absolute confirmation that these ever had much involvement with Roy Allison. Still, the possibility that two giants from the 'golden era' of NE speakerdom had involvement with these one-offs provides sufficient intrigue for me to share this tale, and now I need some detailed assistance.

3 hours ago, ligs said:

The magnet of the unmounted tweeter was probably glued to the back of the woofer magnet at one time

Hi ligs.... and thx for your post, but I haven't got a clue what you are trying to describe here. The pic of the two attached magnets indeed baffled me at first, but I soon realized what had happened to the 'damaged' tweeter (the glue joint failed). How it happened?- - - - we'll never know. The attraction between these two magnets was very strong, and it took some effort to separate them.

Now...who knows how to re-assemble this tweeter? 

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10 hours ago, ra.ra said:

Here's where I need some help. The tweeter VC has continuity and DCR measures at 6.2 ohms (similar to the other) but I'm not sure how best to re-assemble the parts. How to ensure proper alignment? What is the sequence of steps? Any special tools required? What type of adhesives?

My WAG is: pull the cone (of course, that needs to be possible); center and glue the magnet; replace the cone.

My one experience with this was an early AR-3a woofer. The magnet and pole piece try mightily to pull
themselves off center. So you'll need shims and/or a jig to hold them in place.

Epoxy is probably the best option in my mind.

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15 hours ago, ligs said:

see the picture.

Ahh....OK, now I see what you mean - - - yeah, I can understand how that first pic in the second post might suggest a similar double magnet arrangement, but no, this is clearly the tweeter magnet that has wiggled loose.  

15 hours ago, dxho said:

My WAG is: pull the cone ...; center and glue the magnet; replace the cone..... Epoxy is probably the best option in my mind.

This tweeter does not have a cone - - it is a 1-inch dome type - - - and I am just not familiar with what needs to be done for proper re-assembly. Re: epoxy, yeah, I have an easy-to-use two-part epoxy that would probably work well when that time comes. Thx. 

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Still flummoxed about how to re-assemble the tweeter, but a few random thoughts here. First pic is not particularly germane - - rather just for general interest - - but it shows an ADS tweeter of similar construction but with the large added donut magnet like ligs showed in his post.

Pics 2 and 3 (poor quality, I know.....apologies) depict and describe construction of early ADS tweeters, and it occurred to me while reading this that my tweeter most likely contained ferrofluid, as I am guessing with the final image.

Can this tweeter be repaired? Between the two mating surfaces that require re-adhesion, there are no foolproof lugs or physical clues to ensure proper alignment when re-gluing. On top of that, my experience with installing new fluid is nonexistent. Further, the magnetic attraction between these two pieces that need re-attachment is so strong that there is no way to delicately position these two components together allowing facility for minor adjustment. :wacko:

ads L310B tweeter.jpg

ads tweet 1.jpg

ads tweet 2.jpg

tweet VC 1.1.jpg

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On 9/21/2018 at 9:40 PM, dxho said:

So you'll need shims and/or a jig to hold them in place......Epoxy is probably the best option in my mind.

"Sound" advice from dxho, I think. 

Am trying to revive this project to see if I can overcome my inexperience in this area and find a solution to repair this tweeter that had become dis-assembled. Apparently, I couldn't see the full problem clearly before, but now I understand that the challenge is to re-attach the gold-color top plate of the motor structure, where the original adhesive has failed and become detached from the dark grey magnet. The magnetic attraction between these pieces is so strong that, working freehand, it's near impossible to situate the ring properly atop the magnet, even in a dry run without any adhesive present. 

Pic 1 shows good tweet on left and problem tweet on right, with evidence of ferrofluid confirmation shown on scrap of white cardstock. Foreground of Pic 2 shows the ring plate that requires re-attach to the magnet; "good" magnet is shown at upper right. Pic 3 shows cylindrical shim, or "jig" as dxho correctly suggests, fitted in the gap of the good tweeter. It is made from a few layers of continuous flexible acetate, which were allowed to "relax" to fill the circumference of the inner hole of the gold plate, and then fixed into shape with cellophane tape. Pic 4 shows this "tube" fitted into the problem tweeter's gap, and then shimmed tight to the pole piece for centering with strips of acetate.

Pics 5 and 6 show the loosened top plate friction-fit over the shimmed cylinder and being lowered towards its magnet mate. Pic 7 shows the results of the magnetic placement after the shims and cylinder have been removed. I'm reasonably pleased with the visual consistency of the resultant gap, but have not yet applied any epoxy adhesive. Am still in "dry" mode, until I procure new fluid.

Anybody see any problems here that should delay me from gluing this up? 

 

tweets open 1.jpg

P1120533.jpg

P1120540.jpg

P1120557.jpg

P1120560.jpg

P1120566.jpg

P1120537.jpg

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looks good to me

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looks good, remove the old glue, use slow drying two part epoxy and clamp it evenly to dry.

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Any update?

Do any of the members who knew Victor Campos and Roy know what they might 

have been working on around 2003? 

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1 hour ago, Pete B said:

Any update?

Nothing since my last post. I work slowly, and I'm involved with too many projects all at once. Have just prepared several parts orders so am now waiting on new ferrofluid to move this along. I'm very pleased with the magnet re-assembly, but it certainly did not require clamps - - the magnetic attraction is so strong that no additional mechanical assistance is necessary. This is the first time I've dissected a tweeter to this level, but I'm looking forward to giving them some fresh juice (fluid), and then some fresh juice (electricity). 

Regarding the provenance of these one-offs, I am unable to vouch for any level of authenticity beyond what I've already stated here. Nonetheless, the guy I purchased these from was extremely knowledgeable, and seemed to get himself in the right place at the right time to pick up these bits of audio history flotsam. I really hope to run into him again at local flea market/swap events once spring arrives so that I can maybe learn a bit more. 

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