Blown Forte II tweeter

[OneMillionWays]

Hi Forum!

I just blew a tweeter in one of my forte IIs. I found the Step-by-Step Diaphragm Replacement for the K-77 Tweeter (EV-35A) page, but I am not sure how to open up the Forte IIs. Is the back glued on?

Alternately, does anyone have any recommendations for a good repair shop or person within an hour or so of Portsmouth, NH?

Thanks,

Tim

[formica]

As far as I know the Forte and Forte II both had their drivers mounted from the front.... so the screws should be exposed when you remove the grill.

Just unscrew the tweeter and carefully pull it forward, and it should come out. Im unsure if the wires are connected with friction connectors to the tweeter, or soldered to it.

Good luck...

Rob

[SCOOTERDOG]

Just as an FYI, keep in mind that the Forte's 1 and 2's use a K75 tweeter and not the K77. Make sure you get the correct diaphram for the K75.

[OneMillionWays]

Thanks!

[Olorin]

Formica and Scooter both give excellent advice. WRT your tweeter, you should find that six or eight screws hold it in place from the front, and friction connectors attach the wires to the tweeters. You shouldn't need to remove any other drivers, unless you drop the wires down into the cabinets . . . then you'll be pulling the passive off the back so you can fish them back up. The wires are color coded, but if you're like me it's not a bad idea to label one of the lugs and one of the wires so you can get them back together right the first time.

[WMcD]

Dear 10^6,

You should be able to do this yourself. It is just a little more complicated than changing a lightbulb. It is nowhere near as complicated as changing out the diaphragm of the K-77.

I replaced a pair of diaphrams on the tweeters on my e-bay Quartets. These are the little brothers to the Forte II.

The back does not come off the speaker box. All drivers are front mounted. Meaning the box is assembled and all mounting is from the front with screws.

First, order a pair of replacement diaphragms from 1-800-KLIPSCH. They are about $20 apiece with shipping and tax. You may want some spares. I bought two spares.

Take off the front grill. It is held on with magnets. Use a butter knife to pry at the edge.

You will see the main woofer, mid and tweeter.

The tweeter is held in place with some Philips screws. The entire tweeter can be removed through the mounting hole. Make some note of the wiring. There are two wires with small automotive type push-on connectors. Probably ground (negative) is black and the positive is some color. There are + and - marks on the tweeter.

None the less, make notes. It would be a good idea to have some masking tape to secure the wires, least they drop back into the box.

Also, look out for a gasket. Keep it in a safe place and it would be nice to make some marks with a pen of which is the top and bottom.

The diaphrams may come with instruction which are 7th generation photocopies from China. Mine were. They will show you how the tweeter is a sandwich of the magnet, the diaphragm unit, and the horn. It is all held together with three bolts and nuts.

The nuts can be backed off with a pair of needle nose pliers. Small vice-grips or the correct small wrench can be used. Probably metric. I didn't worry about it.

You will see that this is simply a matter of changing out the diaphragm plate and putting everything back together.

There was one thing which was not described in the 7th generation photocopy. I found a button of fiber which sits behind the dome of the diaphragm of the original. This was not present in the replacement. Again, this was with the Quartet tweeter. I don't know if it is there with the Forte II version.

It is easy to pick it out of the old one and transplant it to the new one with some tweezers. That is what I did.

Then you're at the step of putting the sandwich back together. It is important to not damage the voice coil, which is a tiny tube of wire attached to the diaphragm. My recall is that the bolts prevent misalighment.

Once you have the tweeter back together is only a matter of putting it back in the box. Look for the polarity markings on the diaphragm plane and your wire. Then the gasket issue.

One thing is that the box is make of medium density fiber board. So you want to be careful with the screws. Don't tighten so much that the screw threads strip out the (junk) delicate MDF.

I did the first one in 30 minutes. The second was done in 10 minutes.

At the time, I was so focused on getting the units working that I did not take photos of the steps. One of our friend here did build up a documentation for the K-77. A Word document with photos.

If you have the photographic equipment, I'd encourage you to do so (perhaps the second one you work on) and publish it to the forum. Many folks would love to have it.

Best,

Gil

[Olorin]

Gil,

Great post. IIRC the Quartet, Academy, Forte II, and Chorus II all share the same tweeter, with the horns varying by model.

[STL]

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On 3/14/2004 11:10:25 PM heretic wrote:

Great post. IIRC the Quartet, Academy, Forte II, and Chorus II all share the same tweeter, with the horns varying by model.

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Actually I think they may all share the same diaphragm and horn lens, but not the same magnet structure. The Chorus II and Cornwall II both use the K79K. The Forte II uses a K75K. The Heresy 2 and Quartet use the K76K.

[Olorin]

Darn you. Now I'm going to have to take my Academy and Chorus tweeters out and look.

[Strabo]

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On 3/14/2004 9:11:15 PM William F. Gil McDermott wrote:

There was one thing which was not described in the 7th generation photocopy. I found a button of fiber which sits behind the dome of the diaphragm of the original. This was not present in the replacement. Again, this was with the Quartet tweeter. I don't know if it is there with the Forte II version.

It is easy to pick it out of the old one and transplant it to the new one with some tweezers. That is what I did.

Best,

Gil

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Nice instructions! Much better than the instructions that came with the tweeter.

I damaged the leads on one of my tweets in my Forte II's last fall and had to replace it.

Yes, the Forte II does have the material behind the diaphram and you can transfer it to the new diaphram with a pair of tweezers as Gil suggests.

I would recommend that you replace both even if one is still good. Better to keep them balanced. Besides, the parts are fairly cheap so no reason to skimp.

Order the replacements from Klipsch. The price is good, and I had mine about a week after placing my order.

[STL]

heretic,

The Academy uses the K76K. Based on the network schematics and speaker specs, the K79K is the most sensative variant, while the K75K being the next most sensative. Both appear to have the same size magnet struture (but I suspect the strength of the magnet fields within the gap differs). The K76K uses a smaller magnet structure and is less effecient (relatively speaking of course). The K84K also shares the same horns lens but uses and even smaller magnet structure and -- yes you guessed it -- is even less sensative.

[WMcD]

Yes, the much maligned (by me) 7th generation photo copy indicates the same diaphragm is used on roughly a dozen of the Klipsch tweeters.

I inferred that the horn is the same for many and the diaphragm is the same. But sensitivity differ.

Certainly one way to do this is to use different size magnets. Remember that sensitivity or "efficency" is a matter of the Bl product. The B is the strength of the magnetic field in the gap. The l is the length of wire. You may have one l arising from a single type of diaphragm and, particularly, voice coil structure.

Another way is to alter the pole pieces. These are the iron structures which sandwich the magnet itself. They "conduct" the magnetic flux into the gap. Perhaps thinner or thicker ones are used for smaller changes while variations in the magnet size is used for large ones.

Gil