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Old 14th May 2009, 01:37 AM   #1
markzb is offline markzb  Malaysia
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Default How is Quad 57 Treble Diaphragm Charged?

Hi everyone!

Thank you so much for looking. I would be grateful if some of you very knowledgeable gents here could help me out understand something.

I am currently rebuilding my treble panels for my Quad 57. Whilst examining it, something puzzles me.

How does the bias voltage get applied to the Quad 57's treble diaphragm?

If one examines the stator panel, one can see that what Quad did was create a grid of sorts to charge the stator by applying a coating of Aquadag.

-----------------
| | | |
| | | |
| | | |
| | | |
| X X |
| | | |
-----------------

If you look at the rather primitive diagram I created above, what it is trying to represent is 4 "painted on with Aquadag" vertical strips that are connected together via a similar horizontal strip on the top and a horizontal strip on the bottom.

(edit. Please note that the horizontal strips appear way too long. They should only be as wide as the 4 vertical strips. Apologies my ASCII artwork sucks!)

The two spots marked X are where rivets are applied to the stator.
These rivets are in electrical contact with this "grid" and connected ultimately to the bias supply via a screw and tag.

The grid as described above was created by masking certain parts of the stator panel and then spraying it with Aquadag. At the same time, this masking and spraying process was also used to create 3 segments on the panel.

There is a gentleman who has kindly shared a repair job of his on the net which helps tremedously.

If you look at this photo, you will be able to see what I mean by the masking and painting.

http://quadesl.nl/img/treble_panel_rebuild_2.jpg


Now.... what Quad did was they then painted over the entire panel with grey paint.

Furthermore, they then applied something similar to masking tape to cover the 4 vertical "charging" strips above.

Again, this gentlemans sharing of his work really helps....

http://quadesl.nl/img/treble_panel_rebuild_7.jpg

And so the Question!!



With this covering of paint, and also the masking tape, it would seem to me that this has the combined effect of actually preventing the bias supply from reaching the diaphragm!

Of course,we all know the panel works, and so I can only reason that I am looking at this incorrectly.


All I can seem to come up with is that the paint and masking tape actually do conduct at the 1500V that is applied to the "grid" and pass this voltage on to the diaphragm.

I would be really grateful if someone would explain to me the mechanism of how the charge gets on to the diaphragm.

Regards and thanks.

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Old 15th May 2009, 09:07 AM   #2
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Hi markzb

it's difficult to follow your question, probably due to terminology, but....I can't find any reference in your description to the copper strip which feeds the diaphragm......I might be wrong but I'm thinking thats what your question relates to..

try this description..


http://www.integracoustics.com/MUG/M...ey_you/57.html

I hope I was understanding correctly...

regards

Ed
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Old 15th May 2009, 02:26 PM   #3
markzb is offline markzb  Malaysia
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Hi Ed

Thank you for taking the time to reply. Much appreciated.

I did not mention the copper strips because the standard Quad panel discussed here never came with them.

These copper strips are added later on by people who take apart a factory assembled Quad panel to repair it.

Since the original Quad treble panel originally worked without any copper foil present, I would like to better understand how the bias voltage finds its way onto the diaphragm when the "grid" that is supplied this voltage is painted over and then has making tape placed over this painted area.

If the copper strips were present in the standard panel , then I would understand very clearly how it works. As the panel works without them, I am still missing something.

Regards
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Old 15th May 2009, 05:12 PM   #4
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Ok one wire to each stator, where does the third wire get connected?

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Old 15th May 2009, 05:16 PM   #5
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Answer:

http://www.integracoustics.com/MUG/M...you/NewLug.jpg

Which shows that the bias voltage (EHT) is applied via the round part of a rivet that makes physical contact with one point on the diaphragm's surface. You have to make sure you get the new diaphragm's coated surface facing the rivet.

Of the many ways of making contact, apparently this is one...

Edit: wait... http://www.integracoustics.com/MUG/M...u/EHTfoil2.jpg

Maybe it is here...

Hmmmm...

SheldonS will know for certain... he rebuilds them.

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Old 16th May 2009, 12:20 AM   #6
markzb is offline markzb  Malaysia
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Hi Bear

Thanks for your input.

Your link to the picture shows a Quad bass panel which in some ways is a little different in terms of layout and construction to the treble panel which we are discussing here.

Please forget the lug/s for now. They actually will hamper discussions on this as you will soon see. Its actually the two rivets in the photo that are part of the key to this.

Now in the bass panel as you have linked to, it is easy to understand how Quad gets the bias voltage applied to the diaphragm.

Please look at the right bottom edge of your picture. There you can see that there is a white plastic strip that has Aquadag coated on it. You will also see a recessed section where a rivet is fastened to it.

If you look at the top right edge of the photo, you will see this same rivet (and another) standing in isolation on the outside of the panel.

Ok... so there are two of these strips in each half of the bass panel. They run vertically. They have the rivet that allows us to connect to this internal conductive strip. These internal strips have Aquadag on them and they are in contact with the diaphragm.

So what Quad do is they assemble the bass panel. They then place two bolts thru the exact two rivets that can be seen in your photo Bear.. Thus by applying bias voltage via tags and the two bolts, the bias voltage is conducted to both the front and back rivets of the panel. We know that the rivets are also in electrical contact with the internal conductive strips that are also in electrical contact with the bass diaphragm which is coated with nylon.


Now back to the treble panel. It is in many ways the same thing.

You have the same two rivets on each half of the treble panel and two bolts that pass thru the front and back halves of the treble panels. The bias voltage is applied to these two bolts via a tag and wire that is connected to them.

And so, the bolts effectively link the front and rear grid together and apply the bias voltage to both these grids.

But unlike the bass panel, the front and rear conductive grids are painted over and then furthermore masked with tape making it very hard for the bias voltage to get onto the diaphragm.

Now.... the few people who fix them, as best as I can understand them, seem to say that it is these two bolts that are piercing the diaphragm are actually supplying the diaphragm its charge.

If this was indeed so.... then why did Quad go to all the trouble of creating the "grid" in the first place? And then in the case of the treble panel, actually insulate it!



Regards
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Old 16th May 2009, 12:17 PM   #7
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It does seem puzzling at first. Many people have theorized about how the diaphragm gets charged. But the construct is actually exactly the same as for the bass panel.

With the treble panel the charge ring is hidden under the paint and the paper strips (in the middle). The charge ring is believed to be a carbon (aquadag) painted ring on the PVC stators.

So how can it work, despite the insulating paint?

Let's take a look at why a diaphragm charges at all. Why would the charge move to the diaphragm when connected to a high voltage source? At first glance there does not seem to be a closed circuit. But the diaphragm together with the two stators forms a double capacitor and hence closes the circuit. So in fact we are charging a capacitor, and the resistance of the coating is in series with this capacitor and the power supply. (this is a simplified but valid way to look at it, in reality the capacitance and resistance are distributed) So the higher the resistance, the longer it will take to charge the diaphragm. But eventually it will charge to the full polarizing voltage (discounting the effect of leakage currents).

Another way to look at it is to realize that the original coating by Quad (Nylon) has an extremely high surface resistance, in the order of 10E12 and up (!). Hence, a little extra resistance in series, in the form of paint or paper strips, does not make any difference.


The theory about bolts piercing the film and thus providing contact (not to mention 'radiating') is a myth. Neither is it needed to add copper contact strips like mentioned in Sheldon's book.


P.S. I'm the gentleman that took those treble panel rebuild pictures on the quadesl.nl
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Old 16th May 2009, 02:53 PM   #8
markzb is offline markzb  Malaysia
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Hi Arend

Thank you so much for your explanation. It makes sense to me.

I had a hard time believing that "only" these bolts were supplying the bias voltage to the diaphragm.

I also appreciate you pointing out to me the surface resistance of the diaphragm and that the resistance of the "paint and paper" in this context doesn't really add up to be very significant.

I really consider it my good fortune to have met you as you are the owner of that website!

If I may ask you Arend...

1. How long do you think it would take to fully charge a freshly rebuilt treble panel the way Quad originally made it.... i.e. Nylon coating and no copper strips.

2. Do you think it is possible that Quad added the paper tape as a means to increase the diaphragm to stator gap?

3. How did your rebuilt treble panel turn out?

Regards
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Old 16th May 2009, 06:02 PM   #9
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Hi,

The speakers when new would be playing fairly decent in about 5 to 10 minutes maximum. But it can take up to a day to reach full charge, especially when they get older.

The paper is not there to increase the gap but to prevent it from making mechanical noises.

After a couple of attempts the rebuild turned out fine. I really should update the site. But it's totally impractical to do it like that, it was more something to see if it could be done.
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