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Old 12th May 2021, 4:29 pm   #1
DonaldStott
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Default Bush DAC10 Speaker Revisited

I have now restored a number of Bush DAC10s and anyone that knows this set will be familiar with the somewhat 'idiosyncratic' inverted cone Celeston loudspeaker. These speakers are known to buzz and rattle, the problem being that there is no obvious way to access the cone and suspension? Using compressed air in association with my Dyson attachment did help a little but I was concerned about blowing rust and dust into inaccessible places!

I did replace a DAC10 speaker which was beyond repair with a Visaton 5" Full Range Speaker speaker from CPC but these are now 10.21 plus p&p. It's not economical to replace the speaker on every occasion, hence this Revisited Thread.

In a previous Thread I noted that the " ... loudspeaker is scratchy and sounds like there is 'stuff' trapped in the workings or a misaligned suspension? The main magnet is an obvious source of 'rust dust' and it would be good to get 'in about it' to give the speaker a proper clean and check."

I've searched and read almost every DAC10 Thread I could find on this and other Forums but can't find any suggestions on how to remove the front of the speaker. I know that there are two bolts that hold the magnet but loosening these doesn't appear to help?

Does anyone know how these speakers were assembled and, more importantly, how they can be disassembled? I have a couple of scrap speakers from DAC10 donor sets, both buzzy and scratchy, so have no inhibitions about trying anything whatsoever to take them apart!
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Old 12th May 2021, 5:19 pm   #2
Lloyd 1985
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Default Re: Bush DAC10 Speaker Revisited

I’ve revived one of these before, in a little Bush battery valve portable (BP10 I think), I can’t remember how I got it apart now though! I have a feeling the bolts are just for the magnet and pole, and the cover is just stuck on, probably with the glue that sticks the edge of the cone to the frame. Mine was well rusted, and I probably just prised it apart, I’ll have a look in my photo’s, as I’m sure to have taken a few.

Regards
Lloyd
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Old 12th May 2021, 7:19 pm   #3
DonaldStott
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Default Re: Bush DAC10 Speaker Revisited

Thanks Lloyd - it would be great to know how you removed the front cover from the speaker? Any pictures would be brilliant!
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Old 12th May 2021, 7:44 pm   #4
Lloyd 1985
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Default Re: Bush DAC10 Speaker Revisited

It looks like my guess was correct, from the photo's it looks like I bent out the edge of the frame lip, then prised the inner bit out, the edge of the cone was completely gone on that one, and was replaced with a bit of plain white paper! I also had to repair where the cone attached to the voice coil former too, including the coil leadouts. As the photo's show, it was a real mess!

I think the point of failure for these is where the spider/suspension is glued to the magnet, the glue gives up and lets it flap about, creating some of the buzzing noises, but also it lets crud get into the voice coil gap.

Regards,
lloyd
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Old 13th May 2021, 9:16 am   #5
DonaldStott
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Default Re: Bush DAC10 Speaker Revisited

Yeah, success - DAC10 Celeston speaker disassembled!

Thanks to Lloyd, who confirmed that the top plate was just glued in place, it was just a case of working away at the gap between the top and bottom sections with a small pry tool until the glue eventually gave way.

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Lots of rust, dust and other debris to clear away and I can now unbolt the magnet and treat the rust:-

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A bit worried about the voice coil which has seen better days although I'm still reading 3.4 Ohms across the speaker:-

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Once it's all cleaned up I've no idea how I will re-centre the magnet in the voice coil when I re-attach the suspension. In a 'normal' speaker I would use thin plastic or paper shims for this job but don't see any way of doing that with this inverted cone speaker??

Here is the pry tool I used to separate the top and bottom sections:-

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Old 13th May 2021, 9:25 am   #6
Lloyd 1985
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Default Re: Bush DAC10 Speaker Revisited

If you can remove the cone from the back part there is a dust cover over the voice coil just like in normal speakers, that can be removed and then reassemble the speaker with the cone on the other half with the magnet and centre it in the same way you would with a normal speaker. The edge of the cone might need strengthening or rebuilding a little once removed, and when I reassembled mine I purposely left the cover with no glue on it, just in case I need to open it up again!

Regards
Lloyd
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Old 13th May 2021, 12:26 pm   #7
DonaldStott
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Default Re: Bush DAC10 Speaker Revisited

Thanks Lloyd - understood. Time for a new scalpel blade to remove the speaker cone from the back plate to access the dust cap! I've had previous experience of strengthening and rebuilding speaker cones so I should be ok in that department?

A bit concerned about the fragility of the speaker cone where it surrounds the voice coil, in particular the surface that was glued to the magnet - see the circular area that the arrow points to on the picture below:-

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Don't want to exert too much physical pressure here but the old glue is very hard and use of any solvent in this location would prove problematic?

I've cleaned out lots of gunk from the voice coil gap in the magnet using thin strips of paper - what I need is a very, very thin cotton bud or similar?

I also removed the two bolts that I thought held the magnet in place (red circles) but it still won't budge. Does the centre of the magnet (blue circle) have some form of physical connection to the top plate or is it just more glue??

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I'm using Hammerite rust remover to clean up everything and have assumed that this won't be a problem for the outer rim of the magnet?

Hopefully reattaching the speaker cone and getting it centred won't be too much of a challenge! I've favoured using Evo-Stik contact adhesive for such jobs but I understand that glues such as Gorilla Contact Adhesive Clear is repositionable and dries crystal clear?
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Old 13th May 2021, 6:36 pm   #8
Lloyd 1985
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Default Re: Bush DAC10 Speaker Revisited

I wouldn't worry too much about the spider/suspension, it should be ok with the small amount of movement from normal use. As for the old glue, it'd be safe to leave it alone, and just put the new glue on top of the old, that should keep the pressure off it and save it from damage.

A small cotton bud would be good! What I've used in the past to clean out particles from voice coil gaps is just insulation tape, poke it down the gap, poke something else in to stick it to the particles, then peel it off and hopefully the vast majority of the rubbish comes with it, then just repeat until it looks clean. The magnet and the plate with the rust on it should come free, might need some gentle persuasion! The pole is fixed to the frame, so stays put, if you can clean it using sticky tape then there is no need to remove it, which will save you from having to re-centre it afterwards!

The rust remover should do a good job, on mine I ended up sanding the rust off! For glue I used cheap wood glue, does the job, and you have plenty of time to play with it before it sets, I've not used anything else on speakers yet so can't comment on other glues. When reassembling I glued down the spider/suspension first and got it centred, let that set and then went round the edge of the cone.

Regards,
Lloyd
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Old 14th May 2021, 11:42 am   #9
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Default Re: Bush DAC10 Speaker Revisited

Quote:
Originally Posted by Lloyd 1985 View Post
The magnet and the plate with the rust on it should come free, might need some gentle persuasion! The pole is fixed to the frame, so stays put, if you can clean it using sticky tape then there is no need to remove it, which will save you from having to re-centre it afterwards!
Thanks again Lloyd but too late, I've disassembled the magnet which may have been the wrong move?

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Old 15th May 2021, 9:59 am   #10
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Default Re: Bush DAC10 Speaker Revisited

I've just confirmed to myself that disassembling the magnet was indeed the wrong move!

Given the strength of the magnet it's impossible to re-centre the ring on the pole and I should have left it fixed to the frame. Even with my shimming skills this has proved to be completely beyond my abilities!

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I'm assuming that the Celeston assemblers had some form of jig that kept the magnet and ring central while the two retaining bolts were tightened?

What I need to find is a piece of metal tube with the following dimensions:-

Inside diameter : 0.62 inches (15.75mm)

Outside diameter : 0.68 inches (17.46mm)

This would give a voice coil gap of approximately 0.06 inches (1.70mm) and we know what these tolerances need to be like to avoid rubbing/scratching!

As I said in my opening Post "I have a couple of scrap speakers from DAC10 donor sets, both buzzy and scratchy, so have no inhibitions about trying anything whatsoever to take them apart". - so I may just consign this current disassembled speaker to the bin and add it to my lessons learned portfolio?
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Old 15th May 2021, 11:02 am   #11
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Default Re: Bush DAC10 Speaker Revisited

Do you have any 16 swg sheet aluminium? You might be able to make a suitable 'part circle' shim by forming the aluminium around something like an appropriately sized socket (as in spanner). Just a thought.

Alan
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Old 15th May 2021, 11:36 am   #12
David G4EBT
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Default Re: Bush DAC10 Speaker Revisited

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Do you have any 16 swg sheet aluminium? You might be able to make a suitable 'part circle' shim by forming the aluminium around something like an appropriately sized socket (as in spanner). Just a thought.

Alan
Sounds good to me: 16 SWG = 1.625mm / 0.0640"

In my socket set an 11mm socket is 15.8mm diameter.

As you say Alan, if not quite a full circle that would give some 'wriggle room' to adjust the diameter to be a good fit.
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Old 15th May 2021, 11:40 am   #13
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Default Re: Bush DAC10 Speaker Revisited

Quote:
Originally Posted by DonaldStott View Post

I may just consign this current disassembled speaker to the bin and add it to my lessons learned portfolio?
Errrm, I don't think you will - 'hoisting the white flag' is not your style!

This little project has got legs and will run for a while yet.
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Old 15th May 2021, 1:28 pm   #14
DonaldStott
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Default Re: Bush DAC10 Speaker Revisited

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Originally Posted by David G4EBT View Post
[Errrm, I don't think you will - 'hoisting the white flag' is not your style!

This little project has got legs and will run for a while yet.
There's a first time for everything?

Quote:
Originally Posted by ajgriff View Post
Do you have any 16 swg sheet aluminium? You might be able to make a suitable 'part circle' shim by forming the aluminium around something like an appropriately sized socket (as in spanner). Just a thought.
Thanks Alan - of course I'll track down some 16 SWG aluminium but I'm really concerned about the tolerances as the speaker cone voice coil will also need to be shimmed from the opposite end making two exercises in shimming for one gap!

Just out of interest does anyone know anything or have access to documentation about the assembly of these 'idiosyncratic' Celestion loudspeakers
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Old 16th May 2021, 6:34 pm   #15
Lloyd 1985
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Default Re: Bush DAC10 Speaker Revisited

Don't bin it yet!! I had the same problem, trying to centre it, there is a little room for error, so don't worry too much about getting the gap exact. I can't remember exactly what I used to shim it, it would probably have been some card, paper or even plastic (whatever was in the recycling bin at the time!). Put the screws back in and leave them so they are not tight, but would hold things in place with a little room to move them, stick something (shim) down the open side of the gap, tap the ring with something to knock it over to the shim side, once the gap looks about right tighten the screws. there will probably be a lot of back and forth with it until it's ok. I normally find there is plenty of room in the ring for the voice coil, but it's the pole that is very tight tolerance, even worse if it's rusty. Once you have the pole centred as best you can, drop the cone on, and if you have a small low powered amplifier of some sort, play some music through the speaker, and move the cone about to see if it can be centred and sound good, there will still be some buzzing with it not being glued, but you should be able to get some idea as to whether or not it's going to be any good.

Regards,
Lloyd
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Old 17th May 2021, 10:28 am   #16
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Default Re: Bush DAC10 Speaker Revisited

Thanks to everyone for their ongoing support and encouragement, especially Lloyd and David.

With the current disassembled Celestion speaker I am convinced that I have gone one step too far when I unbolted the magnet and ring! Don't know if I can get the voice coil centred again but as you would expect I'll have a go! Looking around the house for some suitable material, plastic or metal, that measures around 16 SWG?

It was clear that the voice coil was rubbing as the cone had become detached from the ring above. What my photos don't show is that the connection on the paper cone where the tinsel wire is attached to the coil lead wire was also torn and this has now become detached, snapping one of the lead wires! So I'm left with a length of tinsel wire and a small section of paper cone with a small copper ring and about 2mm of lead wire! I have tinsel wire and lead wire in my supplies.

It may be a terminal case but I'm going to use this as a test bed to see how far I can go in terms of getting the speaker functioning again. It will never be used in a real set so its all just out of interest really and, as I mentioned earlier, will add to my lessons learned portfolio!

I have another DAC10 with a buzzy speaker on my bench (table) currently which has been lashed up temporarily with a KRC-86B Bluetooth module. Using a Tone Generator app on my iPhone you can hear that the buzzing starts at around 200Hz and increases as you go down the frequencies. As to be expected given that at lower frequencies the cone has further to travel. Looking at ways to 'inject' some suitable glue to reattach the suspension without the somewhat risky job of disassembling the speaker!
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Old 17th May 2021, 12:04 pm   #17
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Default Re: Bush DAC10 Speaker Revisited

Make sure you tighten the screws up enough first so that the pole ring doesn't pull then tapping and wedges/spacers should center it up ok.

Lawrence.
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Old 17th May 2021, 7:28 pm   #18
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Default Re: Bush DAC10 Speaker Revisited

Just been pondering the buzzy DAC10:speaker on my bench, not the disassembled one, and thinking back to the speakers I've fixed with suspension problems including a recent DAC90A. On all those occasions I've just used a 1.5V battery connected across the speaker terminals firstly to move the cone out and inject some glue and then secondly to reverse the connections to close the gap and leave overnight. Works a treat and I've tended to use Evo-Stik contact adhesive.

With this DAC10 speaker though when I connect up the battery the cone does move but there is no obvious gap between it and the ring around the top of the magnet. So maybe it's not a suspension problem at all but rust, dust and other gunk in the voice coil gap? No point in trying compressed air as no doubt that will just force debris further down into the gap??

With the disassembled speaker I've been repairing the cone with tissue paper and 50/50 PVA/water - normally dries nice and tight! I think I've also repaired the very small copper ring used to connect the tinsel wire to the lead wires. Everything is drying overnight so we'll know tomorrow morning how things are progressing, or not ...!
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