AL-III ribbon rattle

[RobertR 847]

 Srinath,

 

As to your capabilities in re-engineering Bob’s flawed, lousy designs, I did not and will not comment.  I didn’t think such nonsense worthy of mention.

 

What I did do was to ask two questions. I got an evasive response to the first and no response to the second.  Well then...

 

I have to assume that the answer to both of my questions is NO.  One has to wonder why anyone would continue in trivializing the complexities of ribbon repair, as if it were just as easy as changing a flat tire. This strikes me like somebody with a toothache who decides to extract the tooth himself and plans to then perform his own dental implant, all the while saying, "I can do this!" No, you can't.  You aren't impressing many here, though I fear you might tempt one or two into nasty mistakes; otherwise I'd just ignore the whole thing... 

 

More often than not, faulty ribbons need to be opened up and have the Kapton replaced.  But sometimes ribbons have a problem that doesn't require rebuilding, and the rebuilders will let the customer know when they find that to be the case.   If the owner tries to open it up, rebuilding becomes the only option, other than $hit-canning. This is why it's unwise to open one’s own ribbon.  

 

Fortunately, except for broken magnets, DIY fix attempts on torn up Kapton are not usually an irretrievable disaster, even though the known failure rate to date is exactly 100%.  The driver can generally still be repaired - by the same guys to whom it should have been sent in the first place.  It might take somewhat longer and cost a bit more, as more magnet breakage can result from opening the assembly.  Replacement magnets aren't free and it's a bit messier to get the surviving magnets cleaned up and glued back into their correct places.  

 

 

So there is nothing to gain from pulling your own ribbon apart. Even if you could somehow remove the aging Kapton without tearing it (very unlikely), it is cut shorter now than when it was installed, and there are holes punched all along the edges. There is no place to get hold of it. You will not be able to put it together again successfully. It might just play, at least for a while, but It Won't Sound Right!  Getting an old ribbon reassembled and tensioned correctly would be nearly impossible even for a seasoned pro. But you could be the first.  Good luck. 

 

RobertR

[Daddyjt 9,585]

I am reminded of an all-time great quote by Dirty Harry -

 

"A man's gotta know his limitations..."

[fill35U 1,846]

Srinath-

Like RobertR, I would be *very* interested in your progress if you achieved a working upgrade/redesign for these ribbons. 

 

FWIW, I've spent a few months now researching DIY ribbon drivers. IMO it would be false economy to replace/upgrade magnets in an existing ribbon driver instead of starting from scratch. And you'd be saddled with multiple serious unknowns that driver/speaker manufacturers have the experience and tools to identify and deal with. I think DIY drivers, or even speakers from existing drivers, can be fun and highly educational. I don't think that generally they'll save you money or produce better results than finished commercial designs, unless you're really good or lucky. Subwoofers or limited-range surrounds excepted... full-range speakers are a nightmare! 

 

There's also the issue of originality. Replacing speakers, drivers (or critical parts like magnets or ribbons) with different types is going to have more sonic consequences than just about anything else you could do to your system. Better or worse, the sound will almost certainly be significantly *different*. If that's the goal or is merely acceptable, fine. But I for one would require an awful lot of test data from a reputable third party before I believed that a serious design/construction change improved reliability *and* was at least neutral to the sound. I'm not saying it's impossible, but hats off to you, sir, if you can pull it off! 

[srinath 34]

RobertR: Sorry I dont mean to say I can improve on Carver's work.

But remember these were built in 1980's. In 2014 Neodymium is cheaper than ceramic magnets per unit of magnetic force.

I'd like to think if he was building these today, he would use neodymium.

 

Ribbon re engineering - well beyond where I can improve it at this point. These have vapor deposited aluminum. I cant get anywhere near that for how light it would be and anything I can imagine making will be far too thick and heavy.

 

I pulled my ribbon apart to fix a open in 1 spot. It was right on the end and I fixed it with circuit writer and taped that spot. In fact that spot is a weak spot. The part were ribbon goes into open from the MDF ends. Anyway that part I fixed and have electrical continuity. Not run it after that, cos this guy's pair has a magnet that has moved. These magnets move very easy, even just bringing it from where ever you bought it, if you hit a few bumps on the way, it will drift out.   

 

Cool.

Srinath.

[srinath 34]

Srinath,

A couple of questions on your ribbon work, as I can't help being curious:

Did you ever really take that ribbon all the way apart, somehow without totally destroying the Kapton, or did you stop at the point where the picture shows it?

 

I pulled the other side off, found the break and used circuit writer and got continuity and put a bit of scotch-tape and hope it will prevent it from "flex" shredding itself.

 

Did you ever get that (or any other) malfunctioning Carver ribbon successfully back together again, repaired and working correctly?

RobertR

 

1 Electrical break was fixed. I have a good many more flaws in the 2 ribbons. None are full on breaks - for now.

I am probably going to run the thing a few 100 hours before I go nutzo on fabbing the magnets etc etc. This guy's pair also has issues with magnets getitng knocked out.

 

This is a mechanical operation. I've been doing these since I was a baby. In India I was my dad's lookout when he was pulling his motorcycle apart, cos he would forget the way things go back together, and he was counting on my near photographic memory to tell him how to get it back together. It is no M 1.0 t, it will be put back together, it will work (for 1 second or 100 years) who knows. As it sits its got continuity in all of the 4 legs. I may patch a few more iffy spots with circuit writer and not put tape over those (cos only the edges can be taped IMHO).   

 

Cool.

Srinath.

 

[srinath 34]

 

 

Srinath-

Like RobertR, I would be *very* interested in your progress if you achieved a working upgrade/redesign for these ribbons. 

 

FWIW, I've spent a few months now researching DIY ribbon drivers. IMO it would be false economy to replace/upgrade magnets in an existing ribbon driver instead of starting from scratch. And you'd be saddled with multiple serious unknowns that driver/speaker manufacturers have the experience and tools to identify and deal with. I think DIY drivers, or even speakers from existing drivers, can be fun and highly educational. I don't think that generally they'll save you money or produce better results than finished commercial designs, unless you're really good or lucky. Subwoofers or limited-range surrounds excepted... full-range speakers are a nightmare! 

 

There's also the issue of originality. Replacing speakers, drivers (or critical parts like magnets or ribbons) with different types is going to have more sonic consequences than just about anything else you could do to your system. Better or worse, the sound will almost certainly be significantly *different*. If that's the goal or is merely acceptable, fine. But I for one would require an awful lot of test data from a reputable third party before I believed that a serious design/construction change improved reliability *and* was at least neutral to the sound. I'm not saying it's impossible, but hats off to you, sir, if you can pull it off! 

 

Actually if you have the thing apart, its pretty simple to get the magnetic forces to match.

These would be the quick on steps if you wanted to.

Refer to the pics I posted.

As you take it apart see how far up the plate with out the MDF part sits up off the bottom. As in - how much does the repel firces make it hover.

Weigh the part with out the ribbon and the ceramic magnets. And note down its weight.

Refab that piece with neo's and bolt on strips etc etc. Weight it, If you're weight is higher - you're likely to get a wrong reading, but if its lighter you'd weight it to match the old weight just to make your measurements.

Sit the part with the MDF on the floor.

Use 10-20 long - like 6" long bolts. and stick em even spaced in the holes.

Sit the new plate on top and see how far it hovers.

If it hovers equally you're good.

If it hovers lower - add magnets and repeat.

If it hovers more - remove magnets and repeat.

 

Yea yea painful, and no way it will cost less than a few $100+ - but you'd have a ribbon where the magnets will not drift when you bump them, move them transport them etc etc. But I'd almost guess, more magnetic force will make more spl, but not alter the tone too much, but well, it is different, in reality though.

Cool.

Srinath.   

 

 

 

[RobertR 847]

 

Srinath,

 

Wish you'd spoken about need for circuit writer repair earlier.  It can be employed successfully without splitting the ribbons - much safer, easier, and quicker that way.  The stuff really works, but of course you have to assure you don't bridge the tiny gap between traces...

 

The first time I fixed a 48" ribbon with that stuff I put an ohmmeter on it while it dried.  Started around 30 ohms and as I watched the reading went steadily down.  I stopped watching when it reached under 4 (new ribbon is around 3.6, so not bad).  That ribbon worked OK until it was rebuilt a year or two later, for other reasons.

 

You're certainly right about the perils of transport/bumping. The original glue gets brittle and fails. Loose magnets can flip and destroy the ribbon in a wink.

 

There is extra-thin super glue (often available in hobby stores) that can seep into cracks in dried out original glue and re-secure magnets.  Tricky to apply, of course - maybe a hypo syringe, handled very skillfully. Some magnet locations are more accessible than others, but maybe worth a shot to forestall a complete tear-down. 

  

RR 

[srinath 34]

The part that was broken in this ribbon was the part that was in the end of the ribbon just as it leaves the MDF edge on the bottom. Its not even visible without pulling it apart. That was why I was able to put a little patch of scotch tape on it. The 4 ohm count is about right too. The problem was 2 other legs dont make the 4 ohm cut either. I have to circuit writer a few more.

 

I didn't bridge the conductors across to the adjacent one, its actually quite a bit of distance away, seeing as you're writing on it. Its almost like missing your line on a college ruled piece of paper. Pretty far away.

 

Cool.

Srinath.

[RobertR 847]

The break right at the board edge is very common, and the board can be unscrewed and moved aside for repairing the trace - no need to open the ribbon.  Before reinstalling the board chamfer its touching edge just a little, and the problem is unlikely to re-occur.

 

I guess the problem of avoiding blobbing silver conductive material across two traces depends on how sharp a writer you have and how gooey the liquid is.  It's no big deal, as long as one is aware of the possibility.  If you goof up, the stuff scrapes off easily enough when it is partly dry, using a wooden toothpick or match.

 

RR 

[PMAT 2,038]

This is a gret thread. I've learned a lot. I guess I've been lucky. I have transported 3sets of Amazings with no problems. I was very careful though. I do have one ribbon with a hunk of disintegrated cover stuck between the magnets and the ribbon. No buzzing or sound diff that I can tell.

[srinath 34]

I didn't take it apart any further than the pics.

The mdf and ribbon were not separated.

You do need to pull the plates off right to repair with circuit writer right ?

Thanks.

Srinath.

[RobertR 847]

Yeah -  three little bolts with locking nuts.  Watch out for magnetism with loose hardware around those ribbons.  The contacts are just pressure - they aren't glued or soldered to the traces, just bolted.  If anybody could figure out how to solder to the aluminum, the boards wouldn't even need to have contact foils.

 

The ribbon vibrates right up to the edge of the phenolic, so the 4 aluminum traces can gradually get sort of sawed through there.  That's why it's a good idea to take, say, a utility knife and when the board is removed scrape its edge a little, to dull the boundary where it contacts the ribbon. Same problem, top or bottom - 8 places in all where the trace can open up; and 8 more in the other channel.

 

As with so many gadgets, the more you work on these things, the more you wonder how they ever f'n work at all.  But they do...

 

RR 

 

[srinath 34]

Mine wasn't broken @ the little circuit board area. It was on the part of the ribbon where it goes into the magnet area.

Cool.

Srinath.

[PMAT 2,038]

It's truly amazing that any of this audio works. The brain loves to be fooled.

[RobertR 847]

Srinath,

 

I mis-read, I guess.  If you know where the break is, just use your writer on it, clearing away any excess silver goop that could short two traces together.

 

If you don't know exactly where the break is, an ohmmeter will tell you, but you need a very dull probe and a gentle touch, lest you puncture right through the trace.  

 

The following is for you or anyone who needs it:

 

Looking at the ribbon from the front, we see four aluminum traces running lengthwise.  Two very close together, then a larger gap for the center magnet row, then two more close together.  Counting left to right, call the left-most trace (where the red wire connects) #1.  The red wire connects to the bottom PC board and to trace #1.  When current enters the #1 trace, it passes up to the top, enters the little PC board there and is routed to trace #3, passes down to the bottom, is rerouted to #2 and goes back up again, to be reversed by the top board again and pass down trace #4, where it is connected to the black wire.  There has to be continuity all the way from red wire to black or else you hear nothing.  If there is a short between two traces someplace you will have a continuity reading, but part of the ribbon will produce either no sound or screwed up sound, depending on cases.  And it also might produce a nasty failure in your amp, because the impedance could go way too low.  So check for that 3.6 or 3.7 ohms (with at least one of the two wires unhooked from anything else) - you should be pretty close to that value if all is well. 

 

None of the above applies to the problems of loose, buzzing ribbons, of course - that's a physical problem, not an electrical one. 

 

RobertR 

[srinath 34]

It's truly amazing that any of this audio works. The brain loves to be fooled.

 

LOL, but not really. In this case atleast. Magnetic lines of force in this case run left to right outward from the center. The current direction in the right 2 traces are up, and left traces are down, so when you pass a signal, the entire ribbon moves toward/away from you. Pretty simple.

 

But you see here is a lovely bit of brain foolery for you - a 30" ribbon moves faster than a 60", and 2 X 30's have the same surface area as the 60. So the 30 X 2 is every bit as good as, and better than 1 X 60.

Yet, people like the 60 far more than a 2 X 30 design. Go figure.

I have heard neither, mine are 48's.

 

Cool.

Srinath.

 

[fill35U 1,846]

 

 

But you see here is a lovely bit of brain foolery for you - a 30" ribbon moves faster than a 60", and 2 X 30's have the same surface area as the 60. So the 30 X 2 is every bit as good as, and better than 1 X 60.

Yet, people like the 60 far more than a 2 X 30 design. Go figure.

I have heard neither, mine are 48's.

 

Why would the 30" be any "faster" than the 60"? Assuming they have the same cross-section of construction, then frequency response, sensitivity(per unit length), and distortion should be substantially the same whether they're six inches or six yards long. I'd guess the ends don't act quite the same as the middles, but once you got past a few inches in length it shouldn't be a big deal. 

  

[srinath 34]

I am not able to put it in words, but if you look at smaller ribbons ther have higher freq extension without much loss in lower end freq response, and higher spl. They however are lower power handling.

I have a few amt's and they behave that way too.

 

OK let me explain it if I can. The center of the ribbon will have to extend further in a 60. 2X the length will be 4 X the extension. I dunno, maybe that matters. maybe they have to move further and hence they act like they are slower.

   

You have a point though, and the edge effect is more in a smaller ribbon cos there is 4 edges for the surface area.

 

Cool.

Srinath.

[RobertR 847]

The original 30" ribbons were a different design from the 60", in that the ribbon material had just two traces - just one time, up and back.  So they may well have sounded different.  But most of the "sound" (the voicing) comes from the crossover design anyway, and those changed lots of times.

 

Rebuilt 30" ribbons are now done with the 4-trace ribbon - have been for some years now, as I understand the situation.

 

RobertR 

[srinath 34]

Aaaaaah, That explains it. I can easily see why the 2X30 wont be as good now.

Thanks RobertR.

Srinath.

[RobertR 847]

Actually the old 30" ribbons sounded great, and still do, but they need amp power almost beyond reason to run them to best advantage - real current hogs.  The big improvement in the 60" ribbons was output - around 5dB.

 

RR 

[srinath 34]

That's one of the reasons why I dont have the working AL-III screaming away right now. They are power hogs too.

And why I wanted to mod my M1.0T, and we all know where that went.

Only amp I have that will run those is a Nak PA-7. But it is needing a recap I suspect.

I sold the 7t mono blocks and need something like that now.

Cool.

Srinath.