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Old 22nd May 2005, 04:59 PM   #11
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Default One more thing...

Anyone can get this sort of data by learning to use a circuit simulator. I used SwitcherCAD III which is a full-featured spice based simulator that is distributed freely by Linear Technology on their web site.

To use a simulator like this, you enter the schematic diagram- they have a very easy to use GUI, then you specify the type of simulation you want to do (in this case I used a transient simulation), and the start and stop times. Start defaults to 0. In this circuit, the caps take a while to charge up, so I started the simulation at 10 sec. and ended at 10.5 sec. This ensured there would be plenty of data for the fft spectrum derivation, though you really only need one complete cycle.

The voltage source is a sine wave source with the amplitude set to 1061V which is the 750 Vrms output from the transformer x sq root of 2. That gives a 2122Vpp sine wave which is 750 Vrms.

When using a spice-based simulator you must have a DC path to ground from each and every node in the circuit. That means you can't have two capacitors in series without there being a resistor to ground at their junction. In such a case you use a 1 Giga Ohm resistor or other extremely large value which will not affect the performance of the circuit but will satisfy the requirement of there being a DC path to ground.

There are some good books about using spice simulators and you can learn a lot from the help and example files that come with SwCADIII. The book by Tuinenga is a good place to start. It covers proper use, some tricks, and limitations of the simulator.

Of course, a simulation is a simulation and not reality. But a simulator can give you some insight into circuit behavior that might otherwise be very difficult of impossible figure out on your own. Also, a simulation is only as good as the models it uses.

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Old 30th May 2005, 06:22 PM   #12
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Default Izzy Wizzy Update

Well I made it back to my buddies Acoustat 0ne plus 0nes. I wanted to undo the Izzy Wizzy cap mod in order to compare it to the effect of a lower value load resistor. For the present my buddie is so happy with the Izzy Wizzy cap mod he would not let me remove it. So I paralleled a second 500 M ohm resistor to the factory 500 ohm load resistor to chop the resistance value in half to 250 M ohms. The result was much the same again as found with the Izzy Wizzy mod. This was a nice improvement in detail resolution and overall control. I think that I_Forgot was right about this from the start. I also think that 10 M ohms is all that is needed for saftey sake as well as to keep the panel operating in constant charge mode. While a lower value load resistor might just result in some small loss in overall output as a result of leaky dielectric in older Acoustat panels I do not think anyone hearing the improvements would not care to trade a little level for the benefits this simple mod will yield. Thanks to I_Forgot for his insite and willingness to share. Best regards Moray James.
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Old 31st May 2005, 10:43 PM   #13
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HI

Thanks I_forgot to share his constatation.

My 2+2 were polarised via a 1gig (1000meg) resistor.

I try 20meg and the result was hurge! If the output drop, I didn`t hear any difference, so if a drop occur, this is not significant.

As for the Izzi Wizzi mods, I already use a "big" film caps (0.15uf) So I can`t comment

The best tweak I done were suggested by one friend of me, when I boosted the bias from 4600V to 6850V. (more than that and the panel will exibit some craking noise at high SPL)

The sound is way better and the sensility goes up too.

Martin
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Old 1st June 2005, 03:29 AM   #14
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Etalon90: thanks for your reply with your experience. Lowering the value of the load resistor results in more volts on the diaphragm. The reason that I talked about the posibility of less output was that if your stator wires are a little leaky then as the diaphragm voltage goes up you will reach a point where peak playback levels will arc sooner than with a lower diaphragm voltage. That said as you have found the improvement is well worth the potential loss of overall output. It does not sound as if you have noticed any loss of output at all.
The Izzy Wizzy mod is an additional 0.01 (6KV) bypass cap on the high voltage supply. This will add about 80 extra volts to the supply output and reduce supply ripple. A nice mod why don't you give it a try? Best regards Moray James.
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Old 3rd June 2005, 05:57 AM   #15
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Default Snubberized HV Supply Xformer

I got back over to my buddies place tonight . I snubberized the secondary side of the high voltage step up transformer on his Acoustat 0ne plus 0ne's. I used a 10 ohm resistor in series with a .01 uf cap. This turned out to be a very nice little mod. Easy inexpensive and souns great. Give it a try. Best regards Moray James.
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Old 14th June 2005, 03:32 AM   #16
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Default Choke in HV supply

Rob in NZ has shared the mod of inserting a 10 H choke in series with the high voltage supply. Seems Rob has done the Izzy Wizzy mod to his Acoustats and then some. Rob said that the additional cap filtering was a worth while improvement but that the choke was a transformation.
It would seem that it would also be a good idea to replace the stock 500 Meg ohm load resistor with a (home made daisy chain) carbon resistor as this will be totally non inductive as well as haveing no capacitive component. 30 Meg ohms is a safe bet and your diaphragm charge will go up in voltage too. Check the idea out. A wide bandwidth choke with low capacitance is a bonus. Best regards Moray James.
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Old 14th June 2005, 01:04 PM   #17
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About choke,

Is the 10H choke to remplace the load resistor? or only in serial with it?

I have some 12H choke that may to the job. It`ll interesting to try.

Regards
Martin
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Old 14th June 2005, 05:01 PM   #18
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Guys,

A choke operates by storing energy in a magnetic field. It takes current to set up a magnetic field. There is virtually no current from the bias supply to the speaker diaphragm unless the speaker is shorted - in which case you have a problem that requires something other than a choke to fix- so there virtually no energy stored.

If you're concerned about the impedance of the bias supply at audio frequencies, the resistor (maybe 20-50 Megs ohms) is the component that defines it. The reactance of a 10H choke at say, 120 Hz is minuscule compared to the resistor.

If you are hearing changes in the speaker's sound by adding a choke to the bias supply, I think it is because you expect to hear a change.

When you replace the resistor in the bias supply, be sure you get a HV rated resistor. "Normal" resistors (any resistor that doesn't specifically say "high voltage" in the specs) will self destruct when high voltage is applied. It is a slow process that will take weeks, but your speakers will get steadily quieter until they eventually go silent. You will then discover that the resistor has opened up. This happens even though there is almost no current through the resistor. I found this out the hard way. I think the HV allows some chemical reaction to take place that doesn't normally occur, or occurs much more slowly at low voltages.

I believe Caddock makes HV resistors.

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Old 15th June 2005, 04:01 AM   #19
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Default Choke in HV supply

The choke is in series after the load resistor, between the resistor and the diaphragm. Rob says that bigger is better when it comes to chokes in this application. The suggestion is that the choke helps to damp low lever diaphragm modulation which is caused by energy stored in the stators dielectric. I have a couple of 7 H chokes which I plan to try out in this position. Rob has done a lot of mods to his 0ne plus 0ne's and say this is the real deal. Right or wrong it cannot hurt to give it a try and find out for sure. It will be another week before I can get to my buddies to try this on his speakers. Will post results as soon as I give it a try. Best regards Moray James.
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Old 15th June 2005, 04:50 AM   #20
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Default Re: Choke in HV supply

Quote:
Originally posted by moray james
The suggestion is that the choke helps to damp low lever diaphragm modulation which is caused by energy stored in the stators dielectric.
This is getting too freaky for me...

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