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Old 15th June 2005, 04:41 AM   #21
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Default Me too

I will give this a try to see what happens. If it does not work I will post to confirm that you were indeed correct. If it does work I think that I can tell by now if it is in my head or in my ears. Either way I'll let you know. But if it does work you guys with edumakashun will have to carry the torch forward to figure out why. That's why you guys were given the responsibility of figureing things out ya got the extra noodles. Best regards Moray James.
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Old 16th June 2005, 11:19 AM   #22
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I also lowered the value of the HV series resistor in my Acoustat 11 panals to 25Mohm.
The improvement is remarkable: much better mids and highs.

Why is this ?
The high voltage must be a little higher but it doesn't explain to me the much more detailed sound.
An other explanation could be that each powersupply should have a LOW series resistance, like we all experience in our amplifiers.
So the next question is, how low can we go ?
If we add a big cap from output to ground of the powersupply and there is no or low series resistor,
besides very dangerous, it can burn a hole in the foil if it touches one of the stators.

Anyway, what do you guys think of this ?
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Old 16th June 2005, 01:14 PM   #23
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I try the choke mods

I use an hammond 157G (30H)

As I_forgot said, the choke is useless because is there no current thru it.

And the sound is inchanged. I perceived NO change, nothing.


I`ll try to bypass the load resistor to hear how the sound become... (not 100% bypass but use 1Kohm for security if is there an arc)

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Old 16th June 2005, 02:33 PM   #24
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Don't drop the series resistor below about 20 Mega Ohms.

The resistor is there for two purposes.

1) It ensures constant charge operation of the speaker (along with the high resistance of the diaphragm coating) by limiting the current that can charge/discharge the diaphragm as it moves. This ensures low distortion, especially at low frequencies.

2) It is a safety device that reduces energy available from the bias supply, such as when the speaker arcs. This preserves the speaker's diaphragm by reducing the likelyhood of holes being burned into it.

This is definitely NOT a situation where you want low power supply impedance. That would be dangerous at these voltage levels and completely unnecessary. Low impedance is what you want if you are trying to supply current. The bias supply in an electrostatic speaker is not there to supply current. It is there to supply charge to the diaphragm, and should supply it only as fast as it leaks off the diaphragm into the air and through leakage resistance to ground.

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Old 16th June 2005, 03:50 PM   #25
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Default Choke choking?

Well it looks like the choke idea is chokeng up. I still plan to give this idea a try will be next week or weekend before I can. Then I too will know one way or the other.
I_Forgot said that this supply is quiet. Ok it's quiet but why does the speaker sound better when the supply is turned off? I have also thought that the speakers sound better whenever I bypass the load resistor and run the panels off of the supply (useing old Acoustat panels). the only reason I can see for this is that when the load resistor is bypassed the supply can get more charge onto the diaphragm more quickly. That would help to keep the charge more consistant on the diaphragm. Seems that there is an issue of charge migration here. The surfacr resistivity of the Acoustat panels is not all that high with later models being a bit higher. What is that time constant formula? I_ Forgot what is the resistance value required for a fulrange panel that will keep charge from migrateing assumeing say a 30 Hz bottom end? Quad used 30 Meg ohms with thier nylon coating. Thanks Moray James.
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Old 16th June 2005, 05:24 PM   #26
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Thanks I_Forgot for the answer.

I have seen HV supplies from Final with a 10Mohm series resistor.
The voltage used was approx. 3.5kV, it was a full range panel.
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Old 17th June 2005, 03:57 AM   #27
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Default oops!!!

I am sorry to say that I did not mention that Rob has a cap to ground after the load resistor and before the choke this should make a difference. Regards Moray James.
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Old 29th June 2005, 11:48 PM   #28
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Default Choke Mod

I got over to my buddies place on Sunday to try the choke mod. I inserted a 7 Henry choke in series with the output of the high voltage supply to the speaker. The difference was immediate. The bass/mid now has real slam and impact like a fine dynamic driver. Every thing is cleaner. The speaker has lost some euphonic qualities as there is less smeer to the sound. I am at a loss as to explain why Martin heard nothing (useing 30 H chokes) as the difference is substantial. I will try putting two 7 Henry chokes in series to see if there is additional improvement (will run both panels off of one supply). Best regards Moray James.
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Old 30th June 2005, 02:17 AM   #29
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I'm not sure about the "no current flow, therefore the choke can make no difference" theory. This would be true with pure DC, but all supplies have some noise and with the capacitive load there would be current flow.
Hey Moray, how's life on the Bow these days? Hope your dwelling came through the flooding ok.
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Old 1st July 2005, 12:31 AM   #30
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Default where's the ac

Theory has it that the AC is a result of the dielectric on the stayor wires which charge up and so modulate the diaphragm.
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