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Old 21st January 2011, 05:21 AM   #11
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The stock pinky finger size yellow polyester caps are about as good sounding as you are likely to find. You can always put the stock ones back in. I don't think I can remember seeing any which failed in use. But if you need some I do have some in stock. I have poly prop factory caps which were used for a while and the Mylar yellow ones. Personally I have always like the Mylar caps best.
If your panels are in good condition you can experiment with adding another stage or two to the high voltage ladder to bump up the voltage on the diaphragm. Most stock supplies don't output more than 3Kv and you can go up to 5-6Kv depending upon the condition of your panels. If you start to get arcing just back off by a stage. You want to run as much voltage on the diaphragms as you can. This will give you more level better dynamics and better bass control.
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Old 21st January 2011, 01:10 PM   #12
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Largely on Moray's advice, I replaced all the caps & diodes in the multiplier circuit, and added two legs. It was well worth the effort. (Thanks again, MJ!) Making those changes to the interfaces yielded better dynamics and immediacy, tighter bass, with a more effortless & energetic presentation. I didn't take any measurements but they did seem to play louder than before the changes. While I wouldn't say the differences were astounding or mind-blowing, they were clearly audible and were a good improvement. These were used with a 2+2 which will play louder than a 1+1 but I have no doubt the results I had would apply to the 1+1. I ran the 2+2 full-range with a beefy Hafler DH-500 amp and never popped a fuse or arced. They played much louder than my ears could take.
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Old 22nd January 2011, 03:58 AM   #13
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Quote:
Originally Posted by moray james View Post
The stock pinky finger size yellow polyester caps are about as good sounding as you are likely to find. You can always put the stock ones back in. I don't think I can remember seeing any which failed in use. But if you need some I do have some in stock. I have poly prop factory caps which were used for a while and the Mylar yellow ones. Personally I have always like the Mylar caps best.
If your panels are in good condition you can experiment with adding another stage or two to the high voltage ladder to bump up the voltage on the diaphragm. Most stock supplies don't output more than 3Kv and you can go up to 5-6Kv depending upon the condition of your panels. If you start to get arcing just back off by a stage. You want to run as much voltage on the diaphragms as you can. This will give you more level better dynamics and better bass control.
Very interesting moray , is the upper limit set by the gap ? would Increasing the gap and the voltage improve the sound ?

regards,
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Old 22nd January 2011, 04:47 AM   #14
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Yes gap more or less sets the limit but in old panels dust or contamination can have an impact. You can wash your panels in the tub with a decreasing agent and then rinse 100%. Keep the panels vertical (on edge) when in fluid so as not to stress the diaphragms. You can re tension after if you like. Changing the gap means building new panels which is a good idea but I would not increase the gap more than it is, slightly smaller would be good and use a crossover and sub for far better bass than full range.
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Old 22nd January 2011, 05:05 PM   #15
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Many thanks MJ and Wayne,

MJ, can you send me the cost for caps and, if possible, a complete set of diodes, including a shipping ?
You will find my adress in my profile. Paypal suitable or whatever is ok for you, you're welcome if yo like to fly here for a visit.

Mathieu
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Old 23rd January 2011, 02:13 AM   #16
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Mathieu: I have been charging $15.00 each for the caps so $60.00 for the set of four pieces posted in a small package I would imagine $20.00 postage. My pay pal is morayjamescables@yahoo.com
I know that folks here may howl at this but for a good number of years I have been using 1N4007 generic diodes (2 in series) to replace the stock diodes and have not had a failure yet they cost pennies each use those as they are available anywhere. Best regards Moray James.
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Old 23rd January 2011, 09:40 PM   #17
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Dear Moray James,

I'll change the caps as soon as I receive them. I assume that the orange components on the board are the resistors of the High tension ladder.
3300M means 3300 Mohms. Is that correct and shall I change them too ?

Regards,
Mathieu

Last edited by Acoustannoy; 23rd January 2011 at 09:45 PM.
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Old 23rd January 2011, 09:59 PM   #18
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Originally Posted by Acoustannoy View Post
I assume that the orange components on the board are the resistors of the High tension ladder.
3300M means 3300 Mohms. Is that correct and shall I change them too ?
The orange components labels 3300M would be the HV mutiplier capacitors and are 3300pF.
The are components C6 - C10 in the attached schematic.
If you are replacing them, I would recommend using caps with voltage rating of 2.5kV - 3.0kV.
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Old 23rd January 2011, 10:08 PM   #19
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Quote:
Originally Posted by moray james View Post
I know that folks here may howl at this but for a good number of years I have been using 1N4007 generic diodes (2 in series) to replace the stock diodes and have not had a failure yet they cost pennies each use those as they are available anywhere.
FWIW, the 2 or 3 Acoustat HV supplies that I have measured are driven with about 750VAC which matches Acoustat schematics( I posted one in the previous post). This being the case, the worst case theoretical PIV voltage that the diodes would see would be 750VAC x 1.414 x 2 = 2121 Volts which, I would bet, is pretty much in the noise of the voltage ratings for two 1N4007 in series.

I reality, only the first diode in the supply will see anything close to this voltage. As you work down the chain, the PIV requirements taper off since the actual voltage stored by each capacitor that the individual diodes charge falls off the further down the multiplier you get.
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Old 24th January 2011, 12:47 AM   #20
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All true, but in practice, the caps tend to degrade over time... there is internal migration of the conductive coating on either side of the "puck" of ceramic, this causes leakage... higher voltage caps have a fatter puck, and are more resistant to breakdown. I'd go with 5kV or higher caps.

Measuring along the multiplier the drops appear to be pretty even... about 1.5kv per, iirc...

Since it is cheap enough to get the higher voltage caps, why not?

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