Author Topic: Ribbon Tweeters not working  (Read 12762 times)

Offline BobM

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Ribbon Tweeters not working
« on: June 09, 2012, 06:39:21 AM »
I was burning in a new AC cord overnight on my amp and in the morning I came downstairs and the ribbon tweeter on my Apogee Calipers was not working in the right channel. Bass panel was fine. So I tried to trace it back ...

- swapped interconnects L-R on the CD player - still there
- swapped speaker cables L-R - still there

So the issue is not upstream of the speaker. So I opened them up and played with a multi-meter...
- continuity from binding posts to the inside of the crossover
- continuity on each leg of the crossover to the ribbon
- continuity from one pole of the ribbin to the other pole of the ribbon
- continuity across the tweeter resistor
- no continuity across the 4 parallel crossover caps, but I can register capacitance across them
- continuity across the crossover coil
- with music playing I can read voltage getting to the ribbon and coming out of the ribbon
- tried tapping each crossover component, the ribbon, the wire, checked the solder connections, etc. All are fine and there is no crackle when tapped

I am totally baffled. By all accoounts I can't find a break in the circuit, but there's still no sound coming out of that ribbon tweeter.

Any and all ideas will be appreciated.

Thanks,
Bob
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Offline Triode Pete

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Re: Ribbon Tweeters not working
« Reply #1 on: June 09, 2012, 06:56:13 AM »
Only one thing to do... Buy upgraded Apogees!  :thumb:
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Offline rollo

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Re: Ribbon Tweeters not working
« Reply #2 on: June 09, 2012, 07:37:55 AM »
  Well that sucks. Could there possibly be a stress fracture in the ribbon ? Is there a safety heat cut off ?
   You can have my Pipedreams for $5000 or a pair of Analysis Omegas at 50% off.  :-P.  Hope you can fix them. Bummer.


charles
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Offline richidoo

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Re: Ribbon Tweeters not working
« Reply #3 on: June 09, 2012, 10:00:19 AM »
Bummer Bob... You'll figure it out.

Sounds like either a short in the ribbon which gives you continuity and voltage across the leads, but most of the ribbon is not getting much current.   If you see music voltage >1V across the ribbon then you should hear sound. Check the resistance of the ribbon, I think it should be 1 ohm or something higher than mOhms or 0. You can borrow my DATS to do impedance sweep if you want.

My other thought is the tweeter resistor, if it's in series then it might be bad, but still appears to conduct because of the coil giving an alternate path. Either lift a leg of the coil or pull out that resistor for proper thrashing (measure the value, maybe put an amp through it to heat it up.)

I have faith in your diagnostic abilities... you'll get it!

Offline BobM

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Re: Ribbon Tweeters not working
« Reply #4 on: June 10, 2012, 08:12:32 AM »
You gave me a good idea Rich. I think I can take a short lengt of wire and just try bypassing/jumping each crossover component to hopefully identify the bad one. If none are bad then it must be the ribbon somehow, but there was nothing done to traumatize or otherwise damage it while playing (at low volume) so I can't see how it could be that.
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Offline richidoo

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Re: Ribbon Tweeters not working
« Reply #5 on: June 10, 2012, 08:37:24 AM »
I think I can take a short lengt of wire and just try bypassing/jumping each crossover component to hopefully identify the bad one.

Very clever!

A sure way to make it not a broken ribbon is to order a new ribbon now, before you find the cause.  :-P

Offline tmazz

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Re: Ribbon Tweeters not working
« Reply #6 on: June 10, 2012, 12:22:55 PM »
Bob,

How tough is it to open the cabinets? Perhaps you can open the working one and then compare each reading between the working and the broken unit to find out what differs.
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Offline jimbones

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Re: Ribbon Tweeters not working
« Reply #7 on: June 10, 2012, 05:30:03 PM »
You gave me a good idea Rich. I think I can take a short lengt of wire and just try bypassing/jumping each crossover component to hopefully identify the bad one. If none are bad then it must be the ribbon somehow, but there was nothing done to traumatize or otherwise damage it while playing (at low volume) so I can't see how it could be that.


Err just be careful not to short out any component that is directly across the amplifier output terminals  :duh
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Offline BobM

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Re: Ribbon Tweeters not working
« Reply #8 on: June 11, 2012, 07:43:31 AM »
Good point. Only jump series components, like the resistor (my first suspected culprit).
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Offline BobM

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Re: Ribbon Tweeters not working
« Reply #9 on: June 13, 2012, 07:53:45 AM »
Here's the official reply from Graz, the Apogee forum owner and current parts manufacturer:

"Strange as it seems - magnets - that was my thought also. Insane as it sounds...

Check dc resistance across the ribbon at the wire joints at the bottom. Whilst reading - gently blow on the ribbon to cause a little movement. How does the continuity hold up under motion? It could be there is a small fracture on the ribbon that opens with motion. If this is the case it's not good for your amp!!!"

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Offline richidoo

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Re: Ribbon Tweeters not working
« Reply #10 on: June 13, 2012, 10:24:10 AM »
If that were the case wouldn't the treble sound be intermittent, since the continuity is repeatable at rest position.  But it's a good experiment to move the membrane around manually under test.

I don't see what could happen to the magnets to cause sudden complete silence. All the magnets didn't move or demagged or overheated all at once. It is more likely electrical imo.

Connect an amp directly to the ribbon via a >5W >8 ohm series resistor. Play a 2k sinewave, you can create that in Audacity. Turn up the volume slowly, just to see if you hear any sound. That will test the ribbon/magnets. Even if the break is intermittent, it's only a 9ohm load, so no big current rush at 1-2V. Just don't play it too low freq.

Offline BobM

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Re: Ribbon Tweeters not working
« Reply #11 on: June 13, 2012, 05:03:27 PM »
Well I tried taking a stripped wire and jump the resistor with music playing low - no effect. Then I jumped the 4 parallel caps - no effect. I put the meter across the ribbon terminals where they connect to the crossover on the bottom and got a reading of 2.5. No change when I blew on them. The magnets all look to be perfect - nothing is loose. I've got continuity through the whole crossover, part to part, and the ribbon across the points where it connects, and even at the top of the ribbon from left to right side, and I get a solid resistance reading from the terminal ends where the speaker cable connects. No parts are loose and the solder joins are tight.

It seems to be a complete circuit but there's no sound. I'm totally stumped.
« Last Edit: June 13, 2012, 05:07:22 PM by BobM »
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Offline richidoo

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Re: Ribbon Tweeters not working
« Reply #12 on: June 13, 2012, 06:07:46 PM »
Do you want to borrow my impedance meter (Dayton DATS system), it might show if the driver is sick if the impedance is screwy or if there is an intermittent short or break at a certain freq. It is very easy to use, you install the software, plug into USB, clip the leads to the driver and press the software button. It is a low voltage signal and you can set the sweep range. You could have it by the weekend!
Rich

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Offline StereoNut

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Re: Ribbon Tweeters not working
« Reply #13 on: June 14, 2012, 05:31:05 AM »
Hey Bob, maybe you should try spraying Windex on it!  It worked for the guy in the "My Big Fat Greek Wedding" movie!!! :rofl:
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Offline rollo

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Re: Ribbon Tweeters not working
« Reply #14 on: June 14, 2012, 08:13:20 AM »
  In the meantime if you need to borrow a pair of speakers just let me know.
   My first guess was a cracked ribbon. Bob are they Bi-wired ? As Rich suggested could you just fire up the ribbons ? If you have current you should have sound. I'm stumped as well. What about the guy that rebuilds them ? Give him a call. Good luck.


charles
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