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Yes - hot iron & apply heat for the minimum amount of time possible. :-)) nt

157.128.218.206

andyr

In Reply to: RE: Tweeter problem with 3.3Rs posted by Davy on August 24, 2010 at 16:32:22

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RE: Yes - hot iron & apply heat for the minimum amount of time possible. :-)) nt - Davy 16:53:23 08/24/10 (8)
Hi again Andy,
jsut wanted to ask something else. Its weird, - according to the 3.3R schematic
http://www.integracoustics.com/MUG/MUG/tweaks/xover/3.3xover.html

The tweeter attenuator socket is in series with the tweeter. Having said that both my tweeters still work with nothing shorted in this attenuation socket, - that seems wrong! With something shorted in that socket the tweeters are a little brighter but they definitely do work too with nothing in the slots! Seems bizarre to me
The MGIIIa stock schematic is similar.
Cheers,
Colin
- Tweeter works with no connection in the attenuator socket - neolith 18:04:48 08/24/10 (7)
  That just ain't right. The attenuator resistor or jumper has to be in place for the tweeter to work. Clearly someone has bypassed the jumper which is not a bad idea in itself. So I suspect that the modder screwed it up and the easiest way to do this is with a rotten solder joint. I wouldn't be surprised if the modder also bypassed the fuse as well.
  My suggestion would be to first remove the fuse and see if the tweeters still work. This will put to rest whether the fuse was bypassed or not.
  Next I would open up the panel in the back and look at the wires going to the attenuator socket. I am sure you will see that they have been modified. Then I would get a solder gun and some solder and reheat the joints until the solder flows. Take a listen and see if your problem has gone away. And if the fuse block has been bypassed do the same with the "new" connection as well.
  BTW I would put my money on the tweeter that sounds duller as being the problem child.
  �
  
  I plan to procrastinate my demise for as long as possible. In the meantime, I practice by putting off all the little stuff.
  
  Edits: 08/24/10 08/24/10
  - RE: Tweeter works with no connection in the attenuator socket - Davy 03:12:57 08/25/10 (6)
    Hi Neo,
    Sorry for the slight delay in replying, - time difference here!
    Many thanks for the helpful reply.
    
    Yes something very fishy is going on with the tweeter attenuator if the tweeter works with nothing at all inserted in this slot. I did not try taking the tweeter fuse out. But I did try it with the mid fuse and that does cut the mid when its taken out, - will try the tweeter fuse tonight. I will obviously want the tweeter fuse connected in if its not already for safety reasons. And I will unbypass the tweeter attenuators as I want to tune there with resistors. I will check for bad solder joints. I have some nice lead based solder here.
    
    Its weird that when I short the attenuator or put a resistor in that slot the sound does change, - if I short for example with a piece of wire the tweeter gets a bit brighter than with nothing in there, which is odd I would have thought it would sound the same if its shorted already.
    
    So your hunch is the same as mine?, - its the duller tweeter that is the culprit (either repair or something else wrong). Thats certainly my hunch. I know how these tweeters are supposed to sound, - the duller one is not extending enough for sure and I am 95% sure it does not sound right. I need it sorted out. If I have to buy a whole new tweeter it will be very pricey for me being here (with shipping and taxes, and the cost of sending the old one back) but it will have to be done.
    Have you any thoughts on how I can possibly test if this tweeter is "bad" or not? I can measure the DC resistance of each tweeter to compare them which might tell me something, but it might not. Thats why the thought of swapping the tweeters from speaker to speaker seemed like a good idea to test for sure, but I can see thats not very practical. Do you need a hot gun to get the tweeters out? Andy reckons you just need a soldering iron?
    
    All the best,
    Colin
    - RE: Tweeter works with no connection in the attenuator socket - neolith 08:23:33 08/25/10 (5)
      You would think if someone bypassed the fuse on the tweeter they would do the same with the mid driver as well. I wonder if a resistor was soldered in place behind the panel to avoid using the attenuator socket and that's why the sound changes when you insert a resistor. Only one way to know - unscrew the panel and look.
      I have removed the tweeters from my IIIa's and also replaced the wiring (22 AWG magnet wire - single run). All it took was a screwdriver and a soldering iron. If you are going to check the resistance of the tweeters (I doubt that this will give you any useful information), then you will need to desolder the connnection to the shunt coil and just measure across the two ends of the tweeter avoiding measuring across the capacitor that is in series with the ribbon. My IIIa's measure 2.3 ohm, the 3.3's are about 3.3 ohm. For accurate measurement, check the ohm reading when the two test leads are touching each other and subtract the residual resistance of the meter from your measurements of the tweeter. My meter reads 0.3 ohms.
      �
      
      I plan to procrastinate my demise for as long as possible. In the meantime, I practice by putting off all the little stuff.
      
      Edits: 08/25/10
      - Part of the tweeter mystery solved! - Davy 03:07:14 08/26/10 (3)
        
        In Reply to: RE: Tweeter works with no connection in the attenuator socket posted by neolith on August 25, 2010 at 08:23:33
        
        Hi Neo,
        Well looked behind the panel, - you were dead right, - found a big 1 Ohm 10W wirewound resistor wired in parallel with the terminals of the tweeter attenuation socket! So that partly exaplains why these speakers have a duller treble than I remember a 3 series having. As for the tweeter imbalance, - am not sure yet if its due to one actual tweeter being bad, - not tested them in isolation yet with my NAD power amp, but I suppose its possible there is a bad solder joint there or one of the resistors has a higher resistance than the other (guess this is not that likely though, - they have 3% tolereance). In any case, I am no expert but I think someones gone over a lot of the solder joints behind the panel, - there are brown/orangely marks on the solder, - I think this is signs of the joints being overheated. So I will have to go over them, - do you think I should remove all the old solder and reapply new, or just heat up the current joints and put in a bit of fresh solder?
        The fuse sockets (both of them) are not bypassed.
        The question is, why did someone put these resistors in? Was it to attenuate the tweeters from a personal preference point of view or it is becuase these speakers are fitted with the earlier 2.3 ohm ribbon which require a 1 ohm resistor in series (the crossover does not have it on this newer speaker obviously)? I forgot to check but it seems my easiest why to check is to measure the gap on the back of the tweeter (according to what Andy said), - the old tweeter is about 1/2 and inch and the newer on has a gap of about 3/8 inch. Also the older is 60.6 inches long and the newer type is 60 inches but thats obviously hard to measure! But I think measuring (if I can tell) is easier (but perhpas less conclusive) to finding out which tweeter they have than measuring the DC resistance of them.
        
        So some progress made, - will report how I get on!
        Cheers,
        Colin
        
        So I am hoping removiing the resistors and
        
        On the road to recovery - neolith 06:58:32 08/26/10 (2)
        
        In Reply to: RE: Part of the tweeter mystery solved! posted by Davy on August 26, 2010 at 03:07:14
        
        The brownish stuff on the solder joints is flux. With proper soldering the flux evaporates and the joint looks shiny and smooth. Cold joints often are dull and appear speckled or rough but not always.
        If you pry off the Magnepan labels at the ends of the ribbons (you can re-attach later with silicon glue), you can access the ribbon connectors. Just detach one end (make sure you are removing the wire from the connector and not the aluminum ribbon) and then you can measure the resistance across the ribbons without having to remove them.
        �
        
        I plan to procrastinate my demise for as long as possible. In the meantime, I practice by putting off all the little stuff.
        
        Making further progress! - Davy 17:09:04 08/26/10 (0)
        
        In Reply to: RE: On the road to recovery posted by neolith on August 26, 2010 at 06:58:32
        
        Hi Neo,
        Well I removed those nasty resistors and went over some solder joints. The joints did look browner on the speaker with the duller tweeter. Things do seem better now, - perhaps the tweeters are not 100% balanced but there are closer and better than befor, - I might be able to fine tune with a 0.5 ohm resistor in the louder one or something. Its certainly not worth buying a new tweeter from Magnepan, - it will set me back about $700 with the shipping at least, - its not worth the money.
        I didn't measure the resistance of the tweeters yet yet but the tweeter gap at the back is about 4.5 mm so I am pretty sure they are the later 3 ohms tweeters with the smaller gap. I remember the tweeters on my Dads MGIIIs looking wider in that gap than these do.
        
        Am sorting out my crossover and things are progressing nicely. The main hurdle to come is sorting out the banana peel on the bass panel of these speakers!, - not looking forward to that. Hopefully the DAP contact cement I ordered from the USA will arrive so so I can get on with this pain of a job!
        
        All the best,
        Colin
        
        RE: On the road to recovery - Davy 08:04:41 08/26/10 (0)
        
        In Reply to: RE: On the road to recovery posted by neolith on August 26, 2010 at 06:58:32
        
        Thanks a lot Neo,
        Yes these solder joints in the panel all look dodgy I think, - brown stuff eveywhere. I will do a photo tonight and of the resistor someone put in there before trying to fix it. Do you think I should remove all the old solder first or just heat up and add some new?
        
        thanks for letting me know how to get to the ribbon connectors, - that great will do that too and measure the reisstance. After I've resoldered the stuff in the panel, removed the resistors, and measured the ribbons resistances I'll see if the tweeters still sound unbalanced. If they do I'll hook they directly up to my NAD 208 power amp thus bypassing the internal crossover, - so I can hear one of the ribbons is at fault or perhpas something in the crossover.
        
        Thanks again,
        Colin
      - RE: Tweeter works with no connection in the attenuator socket - Davy 08:40:23 08/25/10 (0)
        
        In Reply to: RE: Tweeter works with no connection in the attenuator socket posted by neolith on August 25, 2010 at 08:23:33
        
        Hi Neo,
        Yes I agree it weird that someone did not bypass the mid fuse if they went inside the panel. I think bearing in mind the mid fuse is not bypassed its highyl unliekly teh tweeter fuse is.
        There obviously is something over the attenuation slots, - either a short or a resistor, - perhaps they accidentily put two wrong odd value resistors there (I know its unlikely though!) but you never knew. Will find out tongith for sure.
        I agree measureing the ribbon is likely to tell me very little, - I need to test some other wayit, - swapping the tweeters from speaker to speaker is too much work. In my post to Satie today I suggest desoldering the wires and hooking each tweeter directly to a tube power amp to test (with HP signal from my Behringer), - then I can hear if there is any differenc in the HF response of each. I could put a cap in series to prevent oscillation, and just try a low volume test. If there is still a difference then the problem is obviously definitely with one of the tweeters and not the components in the crossover.
        I've not taken a tweeter out of one of these before, - do you know if its possible to access and desolder the tweeter wires without having to actually take the tweeter part way out of the speaker?
        Thanks again for you help,
        Cheers,
        Colin
        
        Edits: 08/25/10
RE: Yes - hot iron & apply heat for the minimum amount of time possible. :-)) nt - Davy 16:36:14 08/24/10 (0)
Thanks Andy,
Understood! Hopefully my tweets might have tabs though!
Cheers,
Colin

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