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Old 5th August 2005, 10:42 PM   #61
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There will always be always some small paths of leakage of the high voltage bias. Even the air gap will have some ionization occurring below hard break down. Other leakage paths can be surface dirt on spacers and dust bridging the gap. These factors vary a lot depending on humidity and age of the ESL. If there is enough leakage current to significantly reduce the bias voltage on the diaphragm due to voltage drop across the large series resistor, this might explain the improvement heard by some folks after reducing a very large series resistor to a smaller value. If an ESL used a 500M resistor and had a 5000V supply, all it would take is 2 micro-amps of leakage to drop the voltage down to 4000 volts. If this were the case, changing the 500M to a 20M might make a noticeable difference in sensitivity, which is sometimes heard as greater detail, etc. There is a real balancing act with this resistor between providing enough current to feed the leakage paths without dropping much voltage, and keeping a constant charge on the diaphragm. Fortunately we can make sure the resistivity of the diaphragm is high enough that we don’t need to rely on the series resistor for all the constant charge effect by itself.

We could envision a choke performing some of the “constant charge duty”, instead of a large resistor, while freely allowing DC current to flow. But the choke would have to have many thousands of henries of inductance. Since the leakage currents are minuscule, you would not need to worry about DCR, nor about air gaps. Then you could wind many thousands of turns of very fine wire on a high permeability core. You would have to take care that the shunt C was very tiny, which would prove very difficult, and you’d have to package the whole beast in an insulating enclosure since the fine wire won’t have enough voltage rating next to a grounded core. A series resistor of a few megs would still be helpful, if only for safety and to damp any resonances. It might be an idea worth pursuing. Any takers?
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Old 6th August 2005, 12:43 AM   #62
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Default tiny chokes

Brian: the one Henry chokes that I picked up surplus are one inch diametre by 3/8 inch thick outside dimensions. They appear to be wound with about 34 guage or smaller wire. This must be approaching what you have in mind no? They were only about $1.25 each. I do plan to series up a couple of these composite ten Henry chokes to compare to just one unit per supply. Let me know if this meets your criteria. Regards Moray James.
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Old 6th August 2005, 04:17 AM   #63
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Moray,

No that’s not quite what I meant. I said I thought it might take THOUSANDS of Henries to ensure approximately constant charge, especially if you wanted to run the ESL down low. That’s why I struggle with the discussion about only 10H making a difference. Let’s say you wanted the choke to present 1Meg of impedance at 100 Hz (which is marginal at best), just for starters, to get a ball-park figure. Well, that’s 1600 Henries. Impossible? No, there are grid bias chokes in that range, for example. If you don’t have to pass any significant current, and DCR can be (and really SHOULD be) as high as possible, then it takes just lots and lots of turns of tiny gauge wire around a gapless high permeability core. There is no dissipated power, so the core would need to be only as big as necessary to fit so many turns around it. At 1 KHZ, such a choke would present 10MEG of Z - IF there were no shunt C, which there will be of course. This part is probably the hardest. I’m no choke winding expert, but I think that keeping the shunt C to few picofarads may be impossible without resorting to many separate series chokes, each of which must have hundreds or thousands of Henries. That might be crazy sounding, but perhaps worth trying. Got ten 500 H chokes on the shelf? (20 for a stereo pair) Not me. You could always add a large resistor in series with these chokes to gild the lily. Maybe 20M.
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Old 27th August 2008, 05:40 AM   #64
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Default 10 H in bias supply

I would like to try this mod on my A. 2+2's But am unsure from reading these posts if I need to change the resistor also, and if I can use / should use iron core/ air core chokes.
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Old 27th August 2008, 07:56 PM   #65
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Default keep the stock 500 meg ohm resistor..

you can look for a surplus one henry choke with a ceramic core and fine wire. The ones I use are about a cm thick and 2.5 cm in dia. the wire gage is quite fine. Don't worry about current capability of the choke as there is very little of that at the end of the supply and the big load resistor deals with what is left over. I use ten in series and I rotate the chokes 90 degees one to the next to keep the fields from coupling up. Let us know what you think about it when you have it all set up.
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Old 30th August 2008, 06:54 AM   #66
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having trouble on the web finding 1 H. inductors. Several chinese companies, but they sell only in huge lots. nothing at radio shack, and parts express only has speaker making inductors one 1H is about $20 (?) bucks.
Cant find anything about suppliers on this site either.
Where can I buy these bad boys?
Thanks.
Paul
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Old 1st September 2008, 04:48 PM   #67
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My 2+2's have medallion and C modificatons done around 1990.
As long as I am pulling things out and soldering should I just replace all of the resistors, capacitors wiring diodes etc. or just the components I've seen recommended in these threads.
(input capacitors, change bias supply resistor from 200Mohm to 20 Mohm and add a .01 cap to bias supply as seen on the Izzy Wizzy (?) site.
While I am at it I was going to add the 10 H inductors after the resistor , and try separating the left and right halves of each speaker to each transformer.
Still having trouble finding 1H inductors tho/
Will start as soon as I can find suppliers.
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Old 5th September 2008, 11:04 PM   #68
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Does anyone have a recommendation for high voltage capacitors for the acoustat mod. I guess the Black Gates are no longer made. At the conventional speaker making sites there are no capacitors rated in the 5000 - 7000 V. range.
Also I was wondering about the Izzy wizzy mod, they recommended 5000 V rated capacitors for C4 & C5, yet these caps aren't in the power supply, but in the audio signal.
I was hoping to replace my capacitors with audio grade capacitors (Musicap, Auricap, etc. ) because these are known to have good sound, But I don't know about just finding a cap on the internet and using it because it's rated at 5000 V
Paul
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Old 6th September 2008, 05:56 PM   #69
Calvin is offline Calvin  Germany
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Hi,

You don´t need ´audio-grade´ caps (whatever is meant with that anyway) in the HV-supply. It´s not only wasted money but truly rubbish. There are often cheap HV-ceramic caps to find. Those are totally ok here. Film caps are already ´over the top´ but can be used too. But again..for the HV-supply You don´t need anything expensive and fancy.

jauu
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Old 7th September 2008, 01:29 PM   #70
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Thanks for the reply Calvin,
Then is there any reason to change the HV supply caps (They are closing in on thirty years old) I do have Medallian & C update.
Also how about c4 & C5 which are in the audio signal not the HV supply, on the Izzy Wizzy site they recommend 5000 V rated caps!
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