Loading cap question

[selmerdave]

I'm considering removing the loading caps on my 604E's as per the suggestion of many people here, but have one issue. One of my speakers has a damaged OUTER covering (the gray external piece that says ALTEC on it), one side of it is actually sheared off. So if I remove the loading caps does there still need to be a seal of some kind behind? Any thoughts on a source for a replacement piece? Thanks.

Dave

[Russellc]

The piece that is "sheared off"...are you talking about the rear cover, (held on by three screws?) or some other part?

Russellc

[selmerdave]

Yes, I guess rear cover would be the term. Gray metal, three screws hold it on and from the back it is the first thing you see. It's a little bent and about 1/3 of it is actually broken off (not sure how that was accomplished). Luckily the diaphragm and everthing underneath is fine.

Dave

[Russellc]

YOU may be using the right term! I just want to make sure which part we are talking about. When this cover is removed if you see a nice dome that is shiney aluminum looking material, you don't have a loading cap. If you see instead, kind of a bake-lite looking semi domned looking thing, that is the loading cap. To remove it, you need two things. one, a felt that is installed in the back of your cap, to prevent reflections off the back of the cap once the loading cap is removed.(please note that the loading cap is the plastic bake-lite looking thing, IT IS NOT a "capacitor", it is a "cap" which fits against the back of the aluminum diaphram, preventing over excursion, and also unfortunately preventing full transient response the driver is capable of. Two, you will need shorter screws to replace the three that are holding the loading cap/diapram assembly in place. The three screws are removed (after removing the leads to the diapram) and now the loading cap/diapram assembly can be removed. At first it looks like it is all one piece, but it isn't. The two are carefully seperated, and the diapram, now sans cap, are reinstalled. The old screws are now too long, because the loading cap's width is no longer there, so you will need shorter screws to tighten the diapram back. Now, the shiney dome is fullt revealed, so be careful with the wires and their reconnection to the diapram! I don't think the broken piece will make any difference, I have heard of people running them with these rear pieces removed. All the parts you need can be purchased for about ten bucks from Great plaines audio. They could probably fix you up with a new rear cover as well.

Let me know how it goes,
AND BE VERY CAREFUL!

Russellc

[Charles Chance]

In addition to what RussellC posted, be very careful with that screwdriver. The magnet will tend to snatch it right into the diaphragm, causing damage to it.

[selmerdave]

Russell,

I DO appreciate your attention to detail, I know this is an awkward thing to go over in text. I am straight on what the exact loading cap is and everything but actually I didn't realize that I would remove the whole loading cap assembly (including the outer ring as opposed to just the cap) and the leads, so I'm a little nervous but I'll probably try it anyway. I'll be careful with the screwdriver, I'd heard that before. I'll let you know about the results.

Dave

[GM]

What 'outer ring'? There isn't one and you don't have to remove the leads either. These should be angled in ~45deg. to clear the cap. If you mean the 'ring' the screws go through, this is the diaphragm assy. base, which doesn't need to be disturbed. The loading cap can be a bear to get off, so I use a sharpened putty knife to slowly work it (or diaphragm when needed) loose/off.

WRT the rear cover, if it allows air to escape then the diaphragm isn't properly loaded, so won't have the same gain as one that doesn't. As for leaving the rear cover off altogether, this will negate much of the horn loading, leaving you with a big tweeter horn with highly non-linear travel in its lower BW. Not a good plan IMO.

GM

[Russellc]

Very true, this can not be said enough! These magnets are extremely powerful. The 900 series (ferrite) can actually snatch screw drivers and other metal tidbits from surprising distances. Once the loading cap is removed, that shiney dome is very vulnerable. Be extremely careful with the screw driver as you approach the screws to tighten the diapram back. Pay attention to the proper lead hookup (phasing) and watch where the wires are going as you replace the rear cap. (unless you are replacing the wires, which you usually will not be doing unless you are replacing an old style diapram with a modern one) They are usually trained to bend away from the diapram as the cover is replaced.

Russellc