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Old 28th January 2014, 12:13 PM   #71
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They get to low normal listening levels. They played for 10-15 mins easy after I unplugged the power supply.

I was using an old Marantz integrated I have. To get this much volume I needed to turn it up half way. The amp when's into protection a few times at this level.


I think I'm going to completely tear down and rebuild the crossovers.

Any other ideas?

Thanks

Eric
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Old 28th January 2014, 12:36 PM   #72
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Oh, Yes you need a big amp to run those.
Something that can swing at least 40Vrms (about 200watts) and can handle a as low as a 2 ohm load without coughing.

jer
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Old 28th January 2014, 12:38 PM   #73
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The only thing I can come up with to help increase the efficiency is to up the bias voltage a bit.

The easiest way to do this would be to add one or two more stages to the voltage multiplier.

jer
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Old 28th January 2014, 12:57 PM   #74
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Everytime you double the bias voltage you get +6db more of efficiency.

Being that the supply has 4 stages (8 diodes) then two more stages would be a good place to start (4 diodes and associated caps).

This would get you to about 3-3.6Kv of bias voltage and you wouldn't have to turn your amp up as high either.

This should be a good value not knowing what the maximum voltage the stepp-up transformer is designed for, but it should be able to handle that range.

As far as a crossover rebuild I would seriously consider an active system first, But that is your call.

FWIW

jer
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Old 29th January 2014, 01:05 AM   #75
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Unfortunately an active crossover isn't in the cards. Since I have all new components for the crossovers save one inductor and one capacitor it would be a lot cheaper to make what I have work.

Either I'm not getting sufficient voltage out of the power supply or something in the crossover is attenuating my mid/high frequencies. The woofers are easily twice as loud as the panels. Maybe more.

I'm going to try and pick up the resistors I need to directly check the PS voltage. If/when I do how many volts am I looking to get if the PS is up to spec?

Thanks

Eric
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Old 29th January 2014, 12:25 PM   #76
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When you get it all setup, Measure the voltage at the point directly out of the multiplier before the other resistors feeding the diaphragm.
It shows a 30Meg in the schematic but by the looks of your photo this is made up of several resistors.

You can however use those as well as long as you can verify their actual value and include that in to your computation of the voltage divider to get an accurate reading.

In all of the dividers I have made I measured each individual resistor and added them all up in order to add the proper amount at the bottm inorder to get the best accuracy I could within 1% or better and then I use a small trimmer to get an exact adjustment.
But you can still get within 5% or better just using off of the shelf parts with out going to such extremes.

If you don't use an opamp buffer you must include your meters input resistance in to the equation.
I have shown in an example that this can be as much of 5% or more error (less voltage than there actually is) in your voltage reading in the posted link below.

Refer to post #37 where Bolserst has calculated the values you should be looking for,

Help me fix these poor ML Sequels

And, Refer to this thread for more info on this exact same matter (particularly starting as post #5),

How to measure bias voltage on Acoustat.

If you already have the crossover components that is fine just make sure that they are of the same values that where already in it.
I don't think that there is any issue with them anyhow unless you actually know that one of the parts is faulty.

ML's are not know for bright sizzling highs from what I gather and remember (11 years ago).
All the FR graphs I have seen, They seem to roll off early quite a bit on the high end.

jer
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Old 16th February 2014, 01:42 AM   #77
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Ok. We may have a problem. I measured the primaries of the audio transformers and I only get .3 ohms. Exactly on both. I switched to new dmm leads and put in new batteries to make sure.

I read a post by Calvin that says this should be less than 10ohms. Well this is less than ten and not a dead short. I also know I get a significant increase in voltage out of them.

Am I OK?

Thanks

Eric
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Old 16th February 2014, 08:40 AM   #78
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What you are measuring is the DC resistance of the winding.

The inductance of the primary winding will determine the impedance that the amplifier will see at the lowest frequency's.

I explain some of that in this post,

Martin Logan Monolith III Transformer Specs

"At the lowest frequency's the ESL's reactance is very very high, and, has little to no effect on the impedance at the lowest frequency's and it is the Transformers primary inductance that determines the impedance at this point."


jer
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Old 5th March 2014, 12:36 AM   #79
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Ok so the Licron spray came today.

Anyone want to suggest the best way to get the panels apart without damaging them?

Will I need to replace the copper strip on the panel?

One nice wet coat will do it with the Licron?

Thanks

Eric
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Old 5th March 2014, 08:58 AM   #80
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I can't help you with getting them apart except that, "Do it Very Very Carefully" so that you don't lift or rip the Diaphragm.

Then once you have them apart clean the diaphragm with some Acetone and/or denatured alcohol.

If you do use acetone make sure that you don't get it on the stator's or any other parts except the diaphragm.
It can/will melt plastics and paints.
But, It won't hurt the Mylar.

Else, Just use Alcohol as it is safer in this matter.

Make that it is absolutely clean with no discolorations coming off on to your cleaning pad.

As according to "How its Made TV" they where lastly coated with a graphite slurry and this has been discussed many time before.

Any that is left over will get encapsulated in the new coating but it is the loose surface particles and residual oils, smoke tar, Finger Prints and dirt that we are concerned about at this point.

Use a lint and oil free cloth or paper towel.
I just use a soft paper towel or something as long as it can't scratch the Mylar.

I have used toilet tissue papers as well.
Again just make sure that it is a lint free type that is not oily, and, doesn't break apart easily.
Or else you will have extra work getting the fibers off.
A vacuum cleaner with a soft brush attachment works nicely a well for this.

Before you start coating, "Shake the can Well" !!!

I would also spray some out First to get the supply tube filled up with the consistency of the material that is in the can.

As it will be thinner and not have the same characteristics when you start at the top of your panel by the time you get to the middle and bottom of the panel.

This would be a good time to use that waste, to spray a folded up paper towel or Foam brush with.

If you use a paper towel you will see how the color of the stuff coming out will darken as the mixed material starts to fill the supply tube.

"Do Not Discard This" as you may need to use it shortly!!

As you start spraying use the same overlapping methods that you would use with a can of spray paint.
To insure a nice even and wet coat.

Watch the coating against the light to make sure that the panel is evenly covered and wet.

You may notice it start to bead up causing some dry some spots and there is two things you can do about this.

1#~You can add more to this area or wait for it to cure some and give it a second coat.

Or,

2#~ You can use the paper towel or foam brush that you just wetted and swab the panel as you go.

This may cause some streaking of the coating, But it will still dry pretty very clear for the most part.

Charlie M has more experience at coating larger panels then I do.

But this is the basic process that I used when I reported my first use upon my discovery of the newer "Crystal" version of Licron before anyone else has ever tried it.

Charlie does say that humidity plays the most important role of any cloudiness that may occur.

The very First time I ever sprayed it on to some scrap Mylar to test its durability it was very dry at the time (winter), and, there was no visible indication that there was even a coating on it to begin with !!!

That is how thin the stuff cures too!!

Charlie has confirmed that the coatings thickness is in the order of only a few microns or 1/1000 of a mm!!!

Replacing the copper strip may not be necessary.
But, I would definitely rub it down with some fine steel wool to get it super clean with no oxidation on it.

Else, you can consider using aluminium foil tape or even a simple painted on DIY graphite charge ring if corrosion is a major concern for you.

I have used both of the above methods with no issues of degradative corrosion issues.

Just make sure that you scuff up the aluminium real good as well and it will last for many many years to come.

Using copper for a charge ring is only a purative thing.

It makes NO difference in performance of the panel at such high voltages whether you use a charge ring of a bit more resistance to it or not!

Having to re-do everything because of a poor choice of materials is of the most major concern here!!

When I First built my panels in 2003 I was going to use some Pure Gold conductive spray paint (as a can of it was a bit affordable then) for a charge ring, so that it would never ever corrode!!

Later I found the Nickel Print conductive paint, and, that was a more cost effective solution as it never tarnishes either.

I never did get a can of it and I used aluminium foil instead.

Then in 2010 I discovered my graphite technique and it has yet to fail me since then as well.

Not to mention that it is by far the cheapest method in the cost of materials.

I suppose that it could be made out of a single soft grade pencil.
But I have had a huge jar of it for about 30 years now from when I had First learned to use it as a diaphragm coating.

jer
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