Have my vintage Dual Cl - 160 Speakers died?

A few months ago I picked up a pair of rather funky vintage speakers from a vide grenier (barn sale) here in south west France where I live.

The speakers a mint pair of early 1970's vintage Dual Cl- 160 speakers (4 ohm) have been running nicely in conjunction with my long term Incatech Claymore amp. 

The Claymore has more than enough clout to drive the Dual's comfortably and the sound and tone is lovely. That is however until the other day when I put some music on and the speakers sounded terrible. Really muffled, and like they were hardly being driven?

At first I feared for the amp, but after connecting up my old pair of Mission 731 speakers, it confirmed the amp was fine (phew!)

I then decided to open up the cabinets on the Dual's and have a look inside. All the wiring looked fine and the soldering looked okay. I put the cabinets back together and connected up to the amp again and played some music...still the same problems. As the grilles were off by accident I put my finger against the edge of one of the four tweeters and suddenly the speaker sounded as it should with the woofer being driven correctly. I tried this same thing on the other speaker and lo and behold it also sounded fine if I held the tip of my finger against the tweeter??? In both cases it was the same tweeter, the top left one. As soon as I removed my finger the sound died back to a dull, flat mush?

What the hell is going on? Is this likely to be a capacitor related problem? I don't see how touching the edge of the tweeter solves it? Do you think it is fixable? Thoughts appreciated?

Comments

  • The wiring loom arrangement and xover circuit are needed before even a guess can take place. Are you able to decyfer the set up?
    E.g. are all tweeters fed by separate leads from the xover board or are they in series.
    Do any capacitors look bulged or leaky etc.
    If you are not able to make sense of the above then professional eyes are required.
    You could try sending a private message to member "PAC" to ask for help. He is a speaker specialist.
    It depends on how highly you value the speakers as to how much you wish to spend on repairs
  • I can open up a cabinet and take a photo of the tweeter wiring and the crossovers? Would that help?
  • PACPAC
    edited November 2016
    Touching the tweeter shouldn't normally have the effect you're aluding to except if the tweeter domes have de-bonded from the voicecoil which is a surprisingly common problem with some older tweeters.  I find this a lot with Focal's TD90 and 120K tweeters where the glue has simply hardened, become brittle and the joint has fractured.  The clue is that when you apply a little pressure, the tweeters suddenly spring into life....or at least make a noise!

    It is both unusual and unlikely for a capacitor to suddenly fail, but sometimes I have seen things like under-rated resistors burning out, especially when an amp is dumping too much DC into a crossover circuit and the resistors are upstream of the caps.

    A photo of the crossovers would do no harm.  Sounds to me like your tweeters may be damaged or part of the HF circuit is damaged.  I'd check that the amp isn't clipping or otherwise putting DC onto the outputs (measured as DC voltage across a load.  Check by wiring one of the amp outputs across an 8 or 10 ohm resistor of at least 10 watts rating, and keep the volume low.  Set a multi-meter to a 20 to 50v range and to DC.  If it gives a DC rating, there's your problem).
  • Hi PAC, thanks for your reply.  Some of what you have said is a bit technical for me. As for the tweeters debonding, it seems a little weird that it is the same tweeter on each speaker that has failed? I think I will post the photos I have taken of inside the cabinet to see if there are any clues? Just to confirm, my amp is an Incatech Claymore giving 8 ohms but the Dual speaker are rated at 4 ohms.

    I believe the amp is fine as I connected up a set of Mission 731's to it and they sound fine. Would like to get to the bottom of what is wrong with the Duals though. I will put some pictures up.
  • I thought I would resurrect this thread as I would really like to try and repair my retro 1970's Dual CL160 speakers. I have attached some photos of the interior of the speakers. If you read the start of the thread you will know that the same tweeter out of four has failed on both speakers. They were working fine for several weeks but suddenly both developed an issue with the tweeters???

    Anyway here are some pictures. These are the four tweeters. In each case it is the one bottom left that has failed?

    image


    One of the capacitors? 
    image

    Some of the other wiring!!

    image

    Can anyone help or advise? 
  • Well, the HFs are wired in parallel, presumably to keep the load at 4ohm.

    The wires coming from the black box with the "blobby" solder look dangerously close in your photo.

    The HF unit in question, is bottom left from the rear (as in your photo) or from the front? If you have a dodgy connection within either that would explain all 4 cutting out at least.
  • So tweeters in series when one of them goes don't behave like Christmas tree lights in series when one of them goes.
    I'm learning :-)
  • Not nesca-celery Ben!

    With two drivers wired in normal parallel one would function if the other died, same as four.

    However, more accurately what we have here is four drivers wired in series/parallel.

    It's both but neither! Two negatives wired in series to one pair, two positives wired in series to the other pair and the remaining positive to negative terminals linked across pairs. One dud breaks the signal path.
  • cj66 said:
    Not nesca-celery Ben!

    With two drivers wired in normal parallel one would function if the other died, same as four.

    However, more accurately what we have here is four drivers wired in series/parallel.

    It's both but neither! Two negatives wired in series to one pair, two positives wired in series to the other pair and the remaining positive to negative terminals linked across pairs. One dud breaks the signal path.
    Thanks CJ.
    Well first off, hush my mouth. Somewhere in between reading your penultimate post and posting myself, your clear use of the word "parallel" somehow became "series" in my brain.

    image

    Also, looking at the photograph properly, I can see what you mean about it being both but neither.
    Can you say a bit more about why the design is like this?
    (Won't help Yellsub directly, but I'm interested.)
  • Not entirely!

    I'm guessing 4 HFs are used for greater dispersal to balance the large LF unit response. The wiring is then down to impedance (keeping the overall speaker to 4ohm in this case), phase and load. All to obtain the designers required performance.

    More than that you'll need the specialised quack-from-PAC ;)
  • Thanks CJ.
    Do you think this wiring might make one of the tweeters (i.e. bottom left) more vulnerable in the event of something going wrong (either over a period of years, or some momentary event, or both)?
    I suppose in the event of something going wrong (e.g. the de-bonding mentioned by PAC) and a tweeter failing in both units, even at random the chance of the "same" tweeter in each unit going is still 25% (I think, stats was never my strong point). Which is still a reasonable possibility.
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