Displaced Pole Piece in K-77M. What now?

[Deang]

Yes I know, which is why I use a heat sink.

Hey, even if I didn't solder I would wipe the tabs before connecting a lead to it. So, do I really have to take the thing apart to figure out which is the positive tab? I guess I already know the answer to that question!\

[BEC]

Dean,

I think you would have to open the tweeter up. You can tell by physical examination when you get the diaphragm mount off. Since we know that this one was put together right before, we can assume that the positive side will be the terminal closest to the notch in the magnet gap.

Now for more than you wanted to know, that notch is to allow extra clearance for the VC wire to travel up the outside of the coil. If you look carefully at the outside edge of the VC, you can see the tiny wire. This wire is about 45 degrees from the positive lead. If you were looking at a bare diaphragm, you would also see a red mark on the diaphragm that is to be lined up with that notch. On yours, since it is installed in the dipahragm mount, the gasket covers this red mark.

Just cause it is fun to confuse you, I will go ahead and tell you that there is a "+" sign on one side of the plastic diaphragm mount. It is molded into the plastic and is very hard to see. That is a good thing, really, because it means nothing. The nice lady determined the polarity when she installed the diaphragm in the housing and marked the positive side with a red dye. She did not try to make it come out to match the "+" on the plastic. I doubt she even knows it is there.

Bob

[Deang]

So, what you are trying to tell me is that you don't have a nice old lady working for you.

Thanks for the good info, much appreciated.

[jheis]

By the way, boys and girls, don't forget to take off your watch before you go messing around with powerful magnets - unless you're looking for an excuse to buy a new watch anyway.

James

[tuned4life]

heres a stupid question. what is the defirence between a k 77m and an alinco magnet tweeter, does anyone have one of each that they could post a pics that shows the basic differance. i was aware that newer k 77 m had square magnet and older k 77 had round magnet. i thought they were both alinco magnet type tweeters. if i wanted to by a pair of k 77 m's is there a way to tell if they have weld or plastic ring? thanks for in advance.

[djk]

Don't bother taking apart.

Take a tweeter with known polarity, hook it up to some pink noise. Do same with unknown and place face-to-face with known. If out-of-phase it cancels.

Good for matching pairs too. The more they cancel out-of-phase, the better the match.

[BEC]

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On 7/21/2005 1:00:55 AM tuned4life wrote:

heres a stupid question. what is the defirence between a k 77m and an alinco magnet tweeter, does anyone have one of each that they could post a pics that shows the basic differance. i was aware that newer k 77 m had square magnet and older k 77 had round magnet. i thought they were both alinco magnet type tweeters. if i wanted to by a pair of k 77 m's is there a way to tell if they have weld or plastic ring? thanks for in advance.

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All of the K-77Ms with the square magnets are ceramic. All of the ones with ceramic magnets have the silly plastic washer and are prone to having the pole piece come loose.

Bob Crites

[scriven]

Since a speaker can act like a microphone, could you tell the polarity by placing a scope on the driver inputs, now outputs, make a loud sound in front of the driver and watch the polarity of the produced wave? (Of course, that assumes you have a scope!)

[BEC]

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On 7/25/2005 12:41:07 PM scriven wrote:

Since a speaker can act like a microphone, could you tell the polarity by placing a scope on the driver inputs, now outputs, make a loud sound in front of the driver and watch the polarity of the produced wave? (Of course, that assumes you have a scope!)

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Nope, any sound you can make goes plus and minus. Now perhaps you could put a sinewave into two of them at the same time and using a dual trace scope, see if they are the same or opposite.

Bob

[scriven]

I was thinking of a one shot trigger on the scope watching for the leading edge of an impulse like a clap - not a steady signal. I hadn't thought of the dual trace and a reference speaker!

[BEC]

Mark,

This gets better the more I think about it. You could wire the two tweeters in series and put an acoustic signal into them at the same time. If they are out of phase, the signal would cancel and there should be little or no output. You could look at that on a single trace scope or just run it through a mic preamp and amp and listen to it on a speaker.

Bob

EDIT: I haven't tried this and there may be some good reason it won't work that way. Just seems to me that it could work.

[scriven]

Bob,

That is essentially what djk suggested earlier with the new twist of using a microphone and amplification or scope to monitor the output.

[BEC]

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On 7/25/2005 1:22:31 PM scriven wrote:

Bob,

That is essentially what djk suggested earlier with the new twist of using a microphone and amplification or scope to monitor the output.

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Mark,

I know, and Dennis would, I am sure, be careful in limiting the amount of power he applied to the tweeters. I just sort of cringe every time I think of guys playing with these K-77s without having them hooked to a crossover. Can get expensive in a hurry.

Bob

[djk]

The amplifier I use for pink noise testing is 100mW at 16 ohms maximum, I usually test tweeters at a lower level than this. It is also cap coupled (cannot put out DC).

[pomonabill220]

Howdy All!!!

I dunno if someone already answered (probably so), but the orientation of the magnet determines the phase of the voice coil vs. input hence the acoustic phasing of the speaker.

[BEC]

Bump

[colterphoto1]

I know, and Dennis would, I am sure, be careful in limiting the amount of power he applied to the tweeters. I just sort of cringe every time I think of guys playing with these K-77s without having them hooked to a crossover. Can get expensive in a hurry.

Bob

That's the perfect use for any old crossovers you might have lying around. They don't have to sound fantastic, just divide the frequencies. I set up receiver in my garage to an old AL with leads from the three outputs to alligator clips so I can run test sounds to any driver within it's operating parameters without worrying about blowing anything up.

Now if I can just locate those three K77 diaphrams you sent me. ARRRRGHHHHH

Michael

[TommyC]

Yet another Great post detailing something that I would Never try! []

I sure am glad there are guys out there with the patience to do this type of work! If I tried some of these repairs you would be seeing me on the news as they lead me away either in a straight jacket or prison jumpsuit! []

[pauln]

http://forums.klipsch.com/forums/637925/ShowPost.aspx

New post with K77s for sale, are they the right kind?

[colterphoto1]

I blew my first Klipsch driver, a K77 from a Cornwall, so thought I'd better start repairing some of my stock.

Okay, read the instructions TWICE, got the bench set up all nice and scientist-man like, and began disassembly.

First one disaster. Ceramic magnet, when pulling apart, the horn pops loose of the black piece with solder poles on it. Looks like four little dots of glue there, can I use like RTV to glue it together? (Super doesn't work , too big of gap to fill. It's where the screen and little black rectangular gasket are.

Next, the voice coil form is totally welded to the gap, the pole piece is loose of the back plate, so I can see that I'l have to go through the alignment and magnet/pole reassembly above. No glue held anything on this baby, all pieces loose without even trying. I used utility knife to gently scrape away wire and phenolic from magnet and pole, maybe use some Scotchbrite to polish up and remove any tiny burrs before very thorough cleaning, then realighment?

How does this sound Bob? Or am I potentially wasting a $24 diaphram in this unit? I don't mind paying a small price for learning, but hate to toss one without trying.

I took apart an Alnico unit and everything went as planned, the VC was split in two but came out neatly. These can be a pita.

How much do you charge to do this again?

Michael