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Multi-Way Conventional loudspeakers with crossovers

My Broken Proac 3.8 crossover
My Broken Proac 3.8 crossover
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Old 2nd January 2003, 08:59 PM   #1
ejecta is offline ejecta
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Default My Broken Proac 3.8 crossover

Checking to see if anyone has the specifications and schematic on the Proac Response 3.8 Crossover. My left speaker has a damaged crossover and I was hoping to troubleshoot it and replace what is probably a damaged inductor.
Thanks in advance
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Old 2nd January 2003, 10:46 PM   #2
Bull is offline Bull  United Kingdom
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Get a multi -meter i you have one,or make a conitunity tester from a led or bulb, battery [brand new] and some wires.
Connect the wires to both terminals of the 'damaged' component,and if nothing happens the component is burnt out.
But that only tests whether or not a component works,but if it's working but damaged.
Like some capacitors if they overload,they melt,but it creates a short across the component and still works.
So the best solution is to buy or borrow an Ossiliscope.To see if the component has equal waveforms of what it originally controlled.
So this means.Eg say a inductor rolls off at 2 khz flat,but as it's damaged it rolls off at 12khz but as a clipped waveform.

At least it's easier to tell what is wrong with it,than intergrated circuits or microchips.If an IC is damaged I throw it away,but it's hard to test an IC to see whether or not it's damaged or broken.
So many legs on an IC and only two test leads with a multimeter,i got so confused.
Also the best capacitors are polyproplene,best inductors are air cored.Iron cored damage too easily,electrolyitic capacitor damage easily too.Also a good crossover PCB[Printed Circuit Board] is essensial.Thats why I buy Eminence Crossovers,because they use top of the range components,glass fibre pcb,and a special light bulb/fuse to protect high frequency drivers.
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Old 2nd January 2003, 11:10 PM   #3
Bobken is offline Bobken  United Kingdom
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Hi,

Unless you have physically damaged the inductor whilst you were doing something inside the speaker, it is most unlikely that the inductor is damaged.

Pro-Ac use very substantial components, especially their inductors, and I cannot imagine any normal situation where such an inductor could have become damaged in use.

At a guess, it would be much more likely to be a soldered joint somewhere which has gone open circuit, possibly due to vibration, but that would be a very rare occurrence too.

Also, I doubt if there are many electrolytic capacitors in this quality of speaker (I would expect at least most of them to be plastic films) but if there is a large value electrolytic perhaps shunting the bass driver, check this out as they can deteriorate over time.

The most likely item to have developed problems would be (one or more of) the speaker driver's voice coil(s), (this is about the weakest part in most speakers, electrically) which will only accept a certain amount of abuse before it will burn out.

Overdriving them, or perhaps an amplifier fault which gave rise to a DC voltage at its output could cause this problem.

Anyway, what makes you think that the inductor has become damaged?

Also, don't forget that you have an identical Xover in the other speaker, which is presumably OK, in which case you (or someone with some test gear) can make some comparisons with this, even if you don't know what value all of the components are.

All you would need to test any component on the Xover would be an LCR meter and something to check resistance if this is not included in the meter, and, if you don't have one, most repair shops should be able to do this for you.

If you post a description about the symptoms which are apparent, i.e. there is no midrange sound now, but this changed without any harsh noises being heard first, or there was a 'scraping' sound first and then it went 'dead', or whatever, I will try to help some more.

This sort of problem is very unusual, in my experience, especially with Pro-Acs which are normally very well built inside.

Regards,
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Old 2nd January 2003, 11:51 PM   #4
ejecta is offline ejecta
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Default 3.8 damage

i can see the partially unravelled inductor hanging down inside the cabinet through the lower rear port. I suspect damage during transport loosened the component and let it fall from the crossover. I have yet to take out any of the drivers to see the actual crossover. I want to know the specifications for the parts before I embark on this type of journey, as I fear more than just the inductor my be damaged. I have built speaker crossovers before just messing around but I am not an expert and don't want to wreak havok with my 3.8s
Thanks again for the prompt an courteous replies.
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Old 3rd January 2003, 02:00 AM   #5
Bobken is offline Bobken  United Kingdom
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Default Re: 3.8 damage

Quote:
Originally posted by ejecta
i can see the partially unravelled inductor hanging down inside the cabinet through the lower rear port. I suspect damage during transport loosened the component and let it fall from the crossover. I have yet to take out any of the drivers to see the actual crossover. I want to know the specifications for the parts before I embark on this type of journey, as I fear more than just the inductor my be damaged. I have built speaker crossovers before just messing around but I am not an expert and don't want to wreak havok with my 3.8s
Thanks again for the prompt an courteous replies.

Hi Lee,

Oh that sounds quite easy to sort out, I think.

Wirewound inductors like that are not at all critical to a few turns of wire, believe it or not, and you should be able to rewind most of the unravelled wire neatly back on to the bobbin or whatever, and secure it with some tape. It will then sound as good as new, I assure you!

I have measured a lot of inductors in my time, and even the very best seem to vary by a small amount, which is probably the equivalent of a foot or two of wire, and in some cases several yards!

Look carefully at the enamel on the wire though, and if any is scuffed through to the bare wire (rather unlikely), try some ladies nail polish on it to 'recoat' the damaged part before you wind it back. Any colour will do, but I like Cherry Red, myself, it sounds so much better!!!

Even if the damaged wire shorts back to itself it will cause no harm, but if it bridges across many turns, it will simply reduce the inductor's value, which you don't want.

I am pretty familiar with ProAcs Xovers, although not that particular one, and as I said before, they are usually very ruggedly built and the air cored inductors are quite heavy gauge wire.

I wouldn't mind betting that there will be little else in the way of damage when you look into it, as the other inductors, and the plastic film caps, are quite tough too.

Look to see if the weight of the hanging choke might have put a strain on the leads of any other component, but most likely it will be soldered to a fixed part on the board, rather than direct to another component.

Any damage to a capacitor is usually readily spotted, and cap leads are remarkably strong, but, if pulled to excess, this should show up with the meter test. Inductors are not in any way magical, and if they look OK and measure up alright as far as resistance goes, you will be alright.

You may need to remake perhaps a solder joint, or two, especially if you need to shorten the inductor wire by a turn or so, and that will most likely be all.

If you have already had some experience of Xovers, don't hesitate to have a go, you have nothing to lose, and I will help with any other advice if there is anything else to correct.

You won't wreak any havoc to the speakers, whatever you do, particularly if you are careful, but you must not end up with any unwanted shorts from plus to minus, as this will harm your amplifier.

If you have even a cheap meter you can check each cap and inductor to ensure that it isn't shorted out internally (most unlikely) and when you are satisfied, check the entire speaker from + terminal to - terminal to ensure that there is some small resistance between these, and there is no direct short here.

Inductors will show a low resistance of less than an ohm DC, and caps will slowly 'charge up' but will in the end show a very large DC resistance, if they are OK.

A visual check will most likely show you what needs testing, if anything, since if they don't look damaged you are very unlikely to have any problems, but if you have a meter, take the time to test them all for your own piece of mind.
Also, don't forget what I said before, in that you have another speaker to check against, and comparisons both physical, and with a meter are very valuable.

In any case, if they have been knocked about as you suggest, you may wish to check inside the other speaker too, to make sure all is well.

Let us know how you get on and if you have any further concerns during carrying out the job, and don't take any unneccasry chances, if you are in any doubt, with such a good speaker as that.

If you wish, you are welcome to mail me privately through the Forum.

Regards,
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Old 3rd January 2003, 02:24 AM   #6
ejecta is offline ejecta
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unfortunately it looks as though 2 inductors broke loose from the crossover board, and most unfortunate is that the wires broke off flush with the board itself. I suppose I should remove the board itself and flip it over to create a new solder point for the inductor after i rewind it?
thanks again
what is your direct email address btw
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Old 3rd January 2003, 11:03 AM   #7
Bobken is offline Bobken  United Kingdom
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Quote:
Originally posted by ejecta
unfortunately it looks as though 2 inductors broke loose from the crossover board, and most unfortunate is that the wires broke off flush with the board itself. I suppose I should remove the board itself and flip it over to create a new solder point for the inductor after i rewind it?
thanks again
what is your direct email address btw
Yes, if the board is of the fibreglass type with the wires passing thro (as opposed to having 'tags' sticking up from the board) and soldered on the reverse, this is exactly what you need to do.

Clean up the existing holes in the board (if you have one, a small drill would do it quickly, after removing any remaining wire 'tail').

Otherwise, get the pad hot with your iron and try to wipe the solder and remaining damaged wire end out of the way as much as possible. I find a wooden toothpick is good to poke thro the hole when the solder is molten, and don't hesitate to add some more solder whilst you are doing this (if it seems necessary) as this will make the existing solder flow much more easily, although to most, it might seem counter intuitive.

As I suggested before, you may need to sacrifice a turn or two from the chokes if the ends of the wires are then not long enough to reach thro to be soldered securely, but this will not make any difference, I assure you. Just make certain that the joints are well made, electrically, and mechanically.

A lot of vibration occurs here, when the speakers are in use, and some quite high currents flow too, and you don't want to compromise the sound or future reliability.

If there are any broken Tywraps (the nylon securing straps) you should replace these or maybe use some strong wire with something underneath it to stop the wire from cutting into the coils of the choke, when you tighten it up.

I prefer not to 'publish' my email address here, but you can contact me by mailing me through the Forum. I will lift the 'block' for a while.

You will find it quite easy, I reckon, but let me know if there are any other concerns. My fees for advice are very reasonable!!!

It would be good to know when you have successfully done the job, and at that point, you will wonder why you ever had any concerns at all.

Regards,
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Old 3rd January 2003, 11:55 AM   #8
Saci is offline Saci  Hungary
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Default Reverse engineering

Hi Ejecta,

There is another thread on ProAc 3.8 here:
http://www.diyaudio.com/forums/showt...&threadid=7481

If you have a pair of 3.8 and you have to open it anyway, would you be so kind and do some "reverse engineering" for us ? Everything could be interesting: dimensions, wall thickness, braces, damping, ports, crossover, etc.

Saci
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