Speaker cone rub repair

springhead

I replaced the original blue alnico speaker from my old Fender Pro Junior a couple of years ago as the cone was rubbing. Thinking of selling the amp now and it reminded me I still have the original speaker and could maybe try and fix it.

Is this just a case of cutting off the dust cap and blowing compressed air in the magnet/coil gap?  Possibly in a kill or cure kind of way?  I guess it's not a valuable speaker but I liked the sound of it and could re-use it on another amp - or bin it and save some space in my overflowing garage!

ICBM

It's unlikely to be dust/dirt - the most common causes are an overheated voice coil that's gone out of round, and a bent frame caused by the amp being dropped. Neither of these is usually fixable, although if you're *very* lucky you can sometimes straighten out a frame enough to work, by trial and error.

You could certainly try cutting the dust cap off - cut inside the glue line obviously! - and it's a shot to nothing since you won't do any other damage, and in the unlikely event of fixing it you can glue another one on if you use a slightly larger one.

springhead

I don't think it's overheating, the amp has had a fairly calm life with home use and maybe just a couple of loud rehearsals.  I can remember helping friends with big hifi/small pa speakers with rubbing woofers due to overheating - sometimes turning them 90 or 180 degrees can help.  Possibly only deferring the inevitable.

Interesting on the drop theory, it did have a low height tumble once.  I don't remember the rub being immediately present afterwards but it's not an amp I've used much so possibly that was what did for it.

I'll try a kill or cure cut the cap off and see what happens.

Bygone_Tones

I am not familiar with those speakers, but I would advise against cutting through the dust cap if you can help it. Try and save it then you can glue it back on again. Try a bit of acetone on the dustcap glue if it will not prise off by other means. Cutting it is a last resort.

Coil rub can be caused by many different things, but on a modern speaker it is very likely a damaged coil. Over-heated and mis-shapen, or maybe a coil wire has come loose from the laquer.

If the spider support is similar to a Celestion you might be able to re-align the coil. Just remove the dust cap, uncouple the spider support, shim the voice coil with camera film or card, then re-glue the spider back in place. Clean it internally as best you can with compressed air and masking tape if it needs it, or you could run a low frequency signal through it (0hz ideally) at a decent volume and turn it upside down with the dust cap removed to blast out any debris.
 

ICBM

Bygone_Tones said:

or you could run a low frequency signal through it (0hz ideally) at a decent volume

I hope you don't actually mean 0Hz .

That's DC...

Bygone_Tones

ICBM said:

Bygone_Tones said:

or you could run a low frequency signal through it (0hz ideally) at a decent volume

I hope you don't actually mean 0Hz .

That's DC...

No idea what you mean. Im clueless about electrics. The lowest setting on an audio generator.

ICBM

Bygone_Tones said:

No idea what you mean. Im clueless about electrics. The lowest setting on an audio generator. 

Probably about 1Hz on a standard signal generator - or if it's a simple 'audio' generator then it could be as high as 20Hz. My old one goes down to 15.

0Hz means no frequency, ie DC - the last thing you want to put through a speaker for any length of time!

springhead

More good ideas, thank you.  Yes, I can see that face down with very low frequency sine wave wobbling the cone up and down might help shift crud from the gap.  Might give it a go later.

Bygone_Tones

Ah right. Yes it does start at 10 now I look at it.