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Old 3rd October 2011, 01:51 AM   #11
noelm is offline noelm  United States
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Default Re: Yeahhh

Acoustannoy, glad you are getting better sound from the Acoustats.

For the Izzy Wizzy high voltage mod, I added a .022uF 6000 volt Wima polypropolene capacitor to the high voltage circuit in each interface. It had the same effect you described for your .01mfd 5000 volt mod.

I also replaced the 500 MegOhm resistor with a 20 MegOhm one in each interface. The speakers now play a little bit louder and seem to be more dynamic. I remember reading that this mod increases the high voltage to the panels.

The smaller interface cases on my 1+1 speakers do not have enough room for large capacitors such as the ones that Bobzilla used. So I used two Solen 28mfd polypropolene caps for a total of 56mfd. For a bypass cap, I used a .18mfd Jensen paper-in-oil cap. I prefer it over the stock .1mfd polystyrene bypass capacitor.

The improvement in sound was immediately obvious to my friends who are not into audio at all. They commented on the better sound even though I did not tell them that I had modified the interfaces. The speakers are much more relaxed to listen to. I hear more detail. The sound does not "stick" to the panels as much as before.

I also did these mods to a friend's Acoustat 2+2 interfaces. He was happily surprised.
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Old 4th October 2011, 06:32 AM   #12
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Default A little bit of theory ?

Thanks Noelm for your interest !

Two day of listening confirm the improvement given by the additional parralel capacitor.
The result of this mod is so real and positive that I feel the need to go further now...

1 - Replacing the 500Mohm with a 20Mohm ? Looking at the circuitry it should'nt change a lot the value of the High Tension ... Adding a step to the high tension ladder is a safer way (done on my acoustat 1+1).

Pro => The high tension frame is loaded througgh the Tension ladder and the 500Mohm resistor, and acts as a capacitor. Reducing the value of the 500 Mohm capacitor will reduce the damping of the circuitry, not increase the HT level (if I'm right).
But reducing the damping result can provide a little bit 'quicker' impulse response, which could explain the feeling you have of a 'louder' sound

Con => On the other hand, reducing the value of the 500Mohm resistor from 500 to 20 will increase the intensity by a factor > 20x in case of short circuit between the high tension frame and the mylar film. It could definitively make a big hole in the film in case of too loud listening.

2 - The level of sensibility of the sound quality and 3D feeling, to the parrallel capacitor addition, and more generaly the sensibility of the Acoustat to the type of capacitor (polyester, polypropylen..), used in the HT side surprises me a lot. I seems to give a new direction about the possible progresses in reducting the directivity of the electrostatic pannels. I'm gonna make some more investigation in this direction.

3 - Can Acoustatanswerman give us a little help for understanding ?
A global understanding of the kinetic interface would help us I think.
For example, what is the way to calculate the low tension capacitor value (47microfarad,) ? This capacitor is loaded by a transformer, himself loaded by a 1ohm resistor plus the capiacitance of the pannels ? I wonder ...

Did Mr Jim Strickland release a complete theory on these interfaces ?

Many thanks,
Mathieu
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Old 4th October 2011, 10:22 PM   #13
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Quote:
Originally Posted by noelm View Post
For the Izzy Wizzy high voltage mod, I added a .022uF 6000 volt Wima polypropolene capacitor to the high voltage circuit in each interface. It had the same effect you described for your .01mfd 5000 volt mod.

I also replaced the 500 MegOhm resistor with a 20 MegOhm one in each interface. The speakers now play a little bit louder and seem to be more dynamic. I remember reading that this mod increases the high voltage to the panels.
noelm & Acoustannoy,

This topic has been covered before in the following thread.
The discussion did branch off to the addition of large value chokes in the HV feed line.
High Voltage Supply Filtering


In general, the conclusion from my own experiments has been that the majority of the differences/improvements you hear from adding the 0.01uF cap and reducing the value of the 500Mohm resistor are due to the resulting increase in the bias charge on the diaphragm. This is most noticeable on older panels that have developed some leakage. Remember that the Acoustat panels have only a single contact point for charging the diaphragm rather than a ring all the way around the panel.


Also, be advised that the added 0.01uF capacitor charges to the full bias voltage and will store considerably more charge than the unmodified HV supply. So, be carefull and make sure the capacitors are discharged before performing any additional work on the supply.
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Old 5th October 2011, 05:54 AM   #14
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Thanks Bolserst

Nice day,
Mathieu
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Old 5th October 2011, 06:11 AM   #15
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I would rather another approach. The stock 500 meg resistor is as good a sounding one as you are ever likely to find. Rather than change it out for a smaller 20 meg unit add more stages to the multiplier to get the output voltage up. Two additional stages should do the trick, try that first. Best regards Moray James.
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Old 6th October 2011, 05:34 PM   #16
tyu is offline tyu  United States
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Default Get the Bias up

Moray told me to get the bias up years back,best thing too do with Acoustats.
In your stock setup even if parts are new its 4k at best.
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Old 6th October 2011, 06:15 PM   #17
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When I was running interfaces (before I got Servos) I did the multiplier stage mod under Moray's advice and it was worth the small effort and cost.
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Old 6th October 2011, 07:13 PM   #18
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That`s very good that you not only liked the mod but can confirm it for others. The diaphragm coatinf on the Acoustat panel is so low that you really do not have to worry about a conductive ring around the panel the stock coating is very conductive as is and that is a very good reason to leave the high resistance (500 meg ohm) resistor in place to make sure that there is no current on the diaphragm to dopossible damage especiall with the panels being old and the dielectric oon the stator wires breaking down with age. Best regards Moray James.
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Old 6th October 2011, 10:02 PM   #19
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I don't really understand why this mod would make a change in the sound, but if you like it, that's all that matters. (The time-constant of the 500-Mohm resistor combined with the panel's capacitance would suggest that additional filtering would not be necessary.) One negative aspect of this mod is that the power supply will stay charged much longer after removing power, so be sure to discharge it thoroughly before sticking your fingers in there. Increasing the value may be even better, but since I don't understand the mechanism at work here, I can't be sure. Do note that adding the capacitor after the 500-Mohm (instead of before as you have done) is NOT recommended, as some people have suggested. Doing so will violate the contant-charge principal that is the basis for the design, as well as increasing the possibility of panel-damaging arcing. Also, be sure that any capacitor used in this position is rated at least 5000 VDC.
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Old 9th October 2011, 06:11 PM   #20
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Default sunday's music

Nice sunday morning, listening at the pianist Noel Lee and Baryton Bernard Kruysen, singing the Baudelaire poemes put in music by Henri Duparc. Heavens's music...
The old 1+1 never sounded so good in 10 years. Here are photos of the interfaces. You can see
- the modified 47mF cap (I kept the original 10mF and 0,1mF ones
- the additional HT ladder step (caps and diode were changed)
- the additional 0,01 mF/5kV cap.
The wiring is not very professional, and the variable resistors are burnt at some places...


a. I put also photos of the 'Active-passive' filter which is located between the preamp and the amp.
It is a 6db/oct on the photo, which was modified into a 12db/oct.
Such filters give astoning good results in terms of dynamics and transprency. I changed all my active filter stuff against this solution.
Design is done with help of the Micro-cap simulation software.
...To whom it may interest, I designed also such a 2way 12db/oct-18db/oct filter for my Magnepan IIIa, with incredible dynamic results, without any loss of information.

b. Now I would like to bring to the end the 1+1 improvements,
- internal wiring with the same cable brand as the one I use (precisely T.Labs RSC500)
- suppressing the variable resistor in the High frequ. filter
- testing MKP -polypropylen- caps on the HVoltage section
- testing values below 500Mohm for the HV resistor

...Moray can you see if you can find
- MKP or similar polypropylen 0,01uF 6kv resistors (x6). Is a higher value makes sense ?
- two 200Mohm and two 20Mohm HV resistors
- replacement for the 16ohm variable resistor into 2 fix resistors (13ohm and 3ohm) ?

Have a nice sunday,
Mathieu
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Last edited by Acoustannoy; 9th October 2011 at 06:14 PM.
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