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Old 10th April 2005, 07:24 PM   #1
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Location: Clarksville, TN
Unhappy Acoustat 3 panels help

I have a pair of Acoustat 3 panels that have been in storage.
Hooked them up to a Hafler 500 and seemed to sound ok but levels seemed a bit low from what I can remember.
Several days ago I went to use them and I noticed on the right channel a cracking and clipping sound.
It seems to be in the vocal area but it seems that it is driven by low frequency energy.
When listening close I can hear the same distortion on the left channel as well but not nearly as bad.
On the live cut of Hotel California when the kick drum comes it it sounds like the things are going to detstroy the frames.
No stucture damage or tell tale frame problems.
Can't find anything funny looking at the diaphrams.
Could someone have fired the things up with the Hafler 500 and damaged them.
Or could it be a supply problem?
Any ideas and I would be so thankful!

Ted Randall
Clarksville, TN
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Old 10th April 2005, 08:52 PM   #2
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Ted: would be a good guess to check out the high voltage supply. I woud start from the pannel back to the interface box. Check out all the connections and then if you can get your hands on a high voltage probe attachment for your hand held multi meter then check the voltage at the output of the HT supply. That should read at around 4-5 KV but 3.5 id still ok (and good for high humidity areas). Make sure to check on both sides of the HT load resistor which is a big long resistor with a spiral track on it . This resistor connects directly to the female pin connector that you use to plug the speaker pannel in (directly between the two thumb screws where the speaker stator wires connect on the circuit board. If you still don't find proper voltage have a look at the step up supply transformer. If memory serves me you should read 120 volts going into that transformer and about 750 volts going out. I you are good at the supply transformer then either you have a bad diode or capacitor somewhere in the high voltage step up ladder. You can use the probe on the step up ladder and find out where the problem part is. You should be able to use your good working supply as a reference to the bad one to get an idea of where problems may be. Good luck. PS should you get everything working again you might want to consider building a new set of MDF frames and set up with just two pannels per channel ala one plus one which will image and stage far better than the wider model three.
Also yo may want to take this oppurtunity to use a heat gun to retension you Acoustat diaphragms which have no doubt sagged over the years. You can look for any sign of wrinkles in the diaphragm seen most commonly in the corners of the panel where the wrinkles can flutter and rasp. Keep a safe distance with the heat gun (3-4 inches) and just heat enough to retension the mylar film (remove any signs of wrinkles). Stay away from any holes in the diaphragm as the heat will make them larger. Don't worry too much about holes in the diaphragm as you can't hear them they are just "zero output zones" and do not have much if any real impact on how well the panel will work. I have seen holes as large as a couple of inches diameter on planels which sounded fine in operation (this as a result of excess heat applied while retensioning the diaphragms). Regards Moray James.
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Old 11th April 2005, 04:45 PM   #3
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The acoustat interfaces should have ~5kv output on the center pin of the interface board. Less is NG.

If any less, replace ALL of the HV caps on the multiplier chain. Occasionally a diode dies too.

I just did that for someone.

Using a heat gun on the Acoustat's mylar is of limited value. It's not really shrinkable mylar. But I have managed to reduce some wrinkling in the corners of some cells with a heat gun judiciously applied - it doesn't seem to always work.

I'd not burn any holes.

Once ur in there replace the interface's HF caps with all film (polypropylene is best, but mylar is cheaper and will do) caps. Big improvement in the upper mid's imaging. Big.

Ur best sound will likely be with a higher power triode strapped tube amp...

Oh, as far as I am concerned, stick with the III configuration, unless you don't want bass, or have an external sub/woofer that you really will trust below 100Hz, since the 1 + 1 configuration really lacks bass, and puts the gap between the two cells just about at ear level when listening... not my fav.

_-_-bear


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Old 11th April 2005, 05:02 PM   #4
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Strong probability that your diaphragms are loose and may have even detatched at a few points. They can be retensioned with a heat gun, but that has to be done VERY carefully because of the plastic gridwork's tendency to melt.

Also check the wire attachments to the plastic grid- they can also come loose and have to be reglued.
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Old 13th April 2005, 10:26 PM   #5
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Bass buzz, if it not due to an open stator connection or bad HV supply is often due to the wires on the bottom of the cells coming loose from the styrene glue that holds them in place... check with a bright light and look closely... I've found many cells where this has happenend.

You can repair with judicious use of nylon fishing line to tie it in place, and working upside down underneath with some styrene "coil dope" applying it so that it drips *away* from the diaphragm (that's why ur upside down on ur back, looking up, and with eye protection on...)



_-_-bear

...there now you know another one of my "secret tricks"
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Old 3rd November 2006, 10:15 PM   #6
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Quote:
Originally posted by bear
Bass buzz, if it not due to an open stator connection or bad HV supply is often due to the wires on the bottom of the cells coming loose from the styrene glue that holds them in place... check with a bright light and look closely... I've found many cells where this has happenend.

You can repair with judicious use of nylon fishing line to tie it in place, and working upside down underneath with some styrene "coil dope" applying it so that it drips *away* from the diaphragm (that's why ur upside down on ur back, looking up, and with eye protection on...)
...there now you know another one of my "secret tricks"
One of my panels developed a buzz a week or so ago and it was exactly that. With flashlight examination, many more near-failures were found. I did not relish taking the cell apart for the second time (the first was a diaphragm replacement). Following your suggestion, I laid it horizontal and worked from below, but couldn't get the fishing line to get around the wire without threatening diaphragm damage.

Plan B was a gentle tug on the wire to pull it back to the bond spot, then give it a drop of a PMMA/cyanoacrylate blend (marketed as "Surehold Plastic Surgery." Fifteen seconds of gentle tug, then overnight just to make sure. Then at each repaired junction, I used a toothpick to apply a dot of Duco Plastic Model Cement and let everything go another night.

Works perfectly- a high SPL workout with Howard Johnson's "Gravity" (a jazz tuba ensemble) didn't shake anything loose.
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Old 4th November 2006, 02:37 AM   #7
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Default Ya can run....

but ya can't hide. Your panels are telling you it is time to build new ones. Start them now and by the time you need to make additional repairs they might be ready. Use 3.8 micron film and 3/8 inch tyhick louvre and 30 gage heavy build Essex magnet wire twenty wires per inch. You will wish that you had done it sooner. Good to hear that you got them going buzz free. Regards Moray James.
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