| High Voltage Supply Filtering - Click HERE for Original Thread |
| moray james |
Don't know how many of you out there will be interested but this may give cause for consideration. I just completed modifying a friends Acoustat one plus one's high voltage supplies. The mod that I did is docummented on the Izzy Wizzy Audio site (http://www.izzy-wizzy.com/audio/spkr.html). This discribes the addition of an extra high voltage filter cap on the HT supply multiplier section. This simple mod does everything stated and then some in my opinion. This mod can be applied to most similar multiplier supplies.
An additional mod/diognostic tool is the mod shared by Sheldon stokes several years ago. This involves a neon bulb which is bypassed (paralled) by a small value cap (to catch transients at lamp turn on). The combination lamp/cap is then placed in series with the output of the high voltage supply after the large megohm value load resistor. When the panel looses charge and draws upon the HT supply the lamp lights up to conduct the HT to the diaphragm. As soon as the diaphragm is fully charged the lamp goes out. The neon lamp presents infinate resistance to the supply under these condition and so effectively decouples the diaphragm from the supply. It is as if you had unplugged the supply and the speaker operates in constant charge mode. As soon as the charge on the diaphragm starts to disapate the lamp turns on and reconnects the supply to the diaphragm. In normal operation the neon lamp will flash on and off. The cool thing is if you should see the lamp on all the time then you know that there must be a steady drain on the diaphragm somewhere (probably dust or bugs between the resistive coating on the diaphragm and the stator on that side of the panel. A very cool diagnostic tool as well as a means to decouple as much as is possible from the supply while maintaining automatic charge management of the diaphragm. Thanks to Sheldon Stokes for that one. Best regards Moray James. |
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| SY |
For whatever reason, I can't seem to reach that page.
I really like a lot of the stuff that is on that site. I tried a variation of the rigid frame last year with much less success; I subbed concrete-filled PVC pipe for the copper. Bad idea. |
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| moray james |
I_Forgot has suggested that he thinks that the Izzy Wizzy mod does what it does not because of additional filtering of the bias supply but because the panel (older Acoustat 0ne plus 0ne) is probably a bit leaky as far as bias supply goes. So if that is the case the the additional 0.01 uf cap stiffens the supply and makes it better able to get more voltage on to the panel. I think that this makes sense. So to find out I will remove the 0.01 uf cap and decrease the resistance value of the load resistor (500M) to say 250M. If voltage on the diaphragn is really the issue then this mod should have an identical result. Any thoughts or suggestions from the forum would be welcome.
I_Forgot has told me that 10 to 50M ohms is plenty to do the job and to keep the speaker working in constant charge mode. This just makes me want a variable supply all the more. Will keep you interested Acoustat owners advised of how this goes. It would be my guess that the reason Acoustat chose such a high value resistor for this job was probably a combination of reduceing current in the event of a shock and a good price from some vendor. Best regards Moray James. |
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| bear |
I use model 3s these days in a homebrew space frame.
The vibration (energy) is virtually all in one plane, so the stiffness needs really only to be very high perpendicular to the panels.
I suggest a mig welder and square tubing. Fill with sand or foam for damping as required.
I used threaded rod/carriage bolts to mount the cells a distance from the main frame... it is possible to adjust the angle of the outer cells. Be sure to use insulation where any metal goes through the cells for mounting, or you'll find things getting charged up... :D
You can apply felt treatment to the frame's surfaces if you are worried at all about reflections at HF.
I found the dumpsters at the local malls to be a treasure trove of premade shapes and after the application of a hacksaw, just stock of chromed & painted square and round steel tubing, btw... ;)
The main effect was to clean up the highs compared to the stock frames. Also the interfaces have long ago had the fuse holders removed and the signal caps replaced with all polypropylene (essential), the internal wiring upgraded and the BPs changed for real ones... the interface sits on the base of the frames at the rear...
_-_-bear
PS. the drop on a neon bulb is ~100v... I'd expect it to "bleep" fairly often while playing? And neon is also a bit noisy, maybe the cap helps with that? Maybe an OB2,3,4 tube?? :- ) |
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| moray james |
Thanks for the reply Bear. You are righr about needing strong frames for the Acoustats. I have seen Two plus Two frames cracked right in half in the middle due to stress from the panels. I have also seen the lag bolts used to mount Acoustat panels pulled out of the Fir strapping they are mounted to by the force of the panels.
What do you think about the Izzy Wizzy mod to the high voltage supply? What do you think about I_Forgot's thoughts on what this mod is doing? I have the feeling that I_Forgot is right. I hope to have the time this weekend to check this out on the 0ne plus 0nes.
I have found that filling the outside edge louver cubes with Duct Seal helps deaden and damp the styrene louvre frame reduceing resonance and cleaning up the sound. It is easy to do , cheap and stays put. A layer of black felt over this row of cubes cleans up the look and makes handeling cleaner. Regards Moray James. |
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| bear |
| quote: | Originally posted by moray james
Thanks for the reply Bear. You are righr about needing strong frames for the Acoustats. I have seen Two plus Two frames cracked right in half in the middle due to stress from the panels. I have also seen the lag bolts used to mount Acoustat panels pulled out of the Fir strapping they are mounted to by the force of the panels.
What do you think about the Izzy Wizzy mod to the high voltage supply? What do you think about I_Forgot's thoughts on what this mod is doing? I have the feeling that I_Forgot is right. I hope to have the time this weekend to check this out on the 0ne plus 0nes.
I have found that filling the outside edge louver cubes with Duct Seal helps deaden and damp the styrene louvre frame reduceing resonance and cleaning up the sound. It is easy to do , cheap and stays put. A layer of black felt over this row of cubes cleans up the look and makes handeling cleaner. Regards Moray James. |
I've not seen the cracked frames, or the bolts pulled out...
The mod is interesting, but I think not so important... the problem, iirc with the extra cap is that it pulls the voltage down, and doesn't really requlate or smooth very much... I like the neon idea best so far!
If ur going full bore and no-holds-barred why not just buy a regulated HV supply? They're small and often adjustable - sometimes you can scavenge them from copiers and printers... or buy them surplus. That solves the entire problem in one shot.
I like the idea of filling the outside cubes with goo... :)
I'll have to give that a try! Thanks for the the thought - good one!
Sil-Pruf silicone might work too... (no acetic acid release). Nice one.
_-_-bear |
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| I_Forgot |
I ran some simulations of the stock bias supply and the "izzy-wizzy" mod version. The Izzy-wizzy modification reduces ripple by about 20 dBV and somewhat increases the average DC output of the supply. 20 dBV sounds like a big reduction, but read on...
I put the results in an excel spreadsheet here:
Acoustat bias supply ripple I used excel because screen shots of the simulator output were just too big. I ran the simulation using SwitcherCad III (a free download from Linear Technology). I added the model of the 1N6533 rectifier to the library to run the simulation. The 1N6533 is a 5 kV, 50 mA rectifier that should be similar to the original parts in the Acoustat bias supply. The SwCadIII schematic file is here: Acoustat bias supply simulation file
Here is the spice netlist: Acoustat bias supply net list
The data includes the spectrum of the ripple so you can see what is going on.
With regards to audibility, I'd say a simple experiment is in order- place your ear close to the speaker with no music playing. If you hear buzzing, then the ripple makes a difference. If not, it doesn't. I have never heard any buzzing from any ESL, regardless of the bias supply configuration, so I'm inclined to think that the ripple really doesn't matter, at least at the levels that voltage multiplier circuits typically produce. The speaker is of balanced construction, so the ripple will cause the diaphragm to be pulled toward each stator, essentially ensuring that the diaphragm doesn't move due to the ripple.
Otherwise the average voltage out of the Izzy-Wizzy mod supply is a little higher, and the difference between the stock supply and izzy-wizzy supply increases as the speaker panel leakage current increases. That means a real leaky panel will show the largest improvement and one that is not leaky may show little or none by making the modification to the power supply. The difference in the output voltage is about 80V for a panel with 500 Mega Ohm leakage. I don't know if 80V is going to make an audible difference or not.
There should be no frequency dependent effects at all, higher voltage just means increased sensitivity (i.e. louder volume) at all frequencies.
I should note that the added capacitor in the bias supply makes servicing of the supply quite a bit more hazardous than the stock supply. If you do the mod, be careful- that extra cap storing the full output voltage (about 5200 V) will pack a real wallop. The fact that it has no bleeder resistor increases the hazard because charge on that cap may persist for weeks after turning the power off. Be careful!
I_F |
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| moray james |
I_F: wow thanks for the detailed explaination, that's a wack of research. Much appreciated, I would have never have learned that on my own! Very interesting and well worth a folder on my hard drive. Do you think I should put a bleeder resistor on that (Izzy Wizzy) cap? If so what is a good value?
This weekend has turned out to be a bust with respect to getting over to my buddies to experiment with the cap mod and your suggestion of decreaseing the load resistor value. I will post back with findings as soon as I gan get over to do the work.
What do the simulations look like with a regulated supply? I would think that there would be a larger difference than that seen with the Izzy Wizzy mod? Thanks again I_F. Best regards Moray James. |
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| 405man |
The idea of the neon indicator is used in the Quad ESL63 where if you remove the grommet at the rear you can see the neon and check its flash rate
Stuart |
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| I_Forgot |
| quote: | Originally posted by moray james
I_F: wow thanks for the detailed explaination, that's a wack of research. Much appreciated, I would have never have learned that on my own! Very interesting and well worth a folder on my hard drive. Do you think I should put a bleeder resistor on that (Izzy Wizzy) cap? If so what is a good value? |
A bleeder would have to be a very large resistor (maybe 1000s of Mega Ohms) or it would pull down the voltage of the bias supply and cancel the effect of adding the cap. Such a large resistor would result in a very long time constant, so its value as a bleeder resistor would be questionable.
| quote: | | [i]What do the simulations look like with a regulated supply? I would think that there would be a larger difference than that seen with the Izzy Wizzy mod? [/B] |
There's regulated and then there's regulated. A regulated supply will maintain a constant average voltage, but the ripple might still be about the same as a charge pump multiplier, maybe even worse. When you look at the ripple in the stock supply, it's level is about 80-100 dB below the average output level. That's pretty good performance, even for a regulated supply. You can find the numbers in the excel file on the ripple spectra page- look at 0 Hz. That's the main output of the supply at DC (0 Hz). Now subtract the value of the 60 Hz output from that.
A regulator that could improve on that performance would be hard/expensive to make, and would not really add to the performance of the speaker, which is why no one does it.
I_F |
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| I_Forgot |
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.
I_F |
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| moray james |
| 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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| etalon90 |
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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| moray james |
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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| moray james |
| 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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| moray james |
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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| etalon90 |
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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| I_Forgot |
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.
I_F |
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| moray james |
| 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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| I_Forgot |
| 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...
I_F |
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| moray james |
| 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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| djmiddelkoop |
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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| etalon90 |
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)
Regards |
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| I_Forgot |
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.
I_F |
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| moray james |
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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| djmiddelkoop |
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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| moray james |
| 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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| moray james |
| 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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| paulb |
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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| moray james |
| 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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| I_Forgot |
Fiddling with things that are of questionable value is a nice hobby if you have the time and energy for it, but in the end, you'll have at best, a slightly tweeked speaker for all your time and effort. ESLs are about as good as speakers can get, except for a few very obvious areas that I will come to in a moment.
Peter Walker didn't sit and play with bias supply tweeks for endless years. He made the bias supply good enough and moved on to other problems. THAT is how REAL progress is made. Sure there are folks who would argue that the goal of a hobbyist is to make it better than commercial equipment, but there is a much better way to approach that, if that's your goal.
What makes a major or useful change to anything? Is it tweeking minor stuff that is of questionable existence, or is it attacking the big problems? If you want to make a real contribution to ESL "knowledge" or performance, you're not going to get anywhere messing with things like bias supplies. Work on the big problems instead. ESL don't play very loudly. Figure out a way to make them do so. ESLs have lousy low bass response. Fix it. ESLs are expensive to make because of the audio transformers. Figure out a way to eliminate the transformers or lower their cost. Figure out an easier way to make the speakers. Some have tried to address some of these problems. Dig up their stuff and learn from it, then try something they didn't.
Just a suggestion...
TD |
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| moray james |
Hey I_Forgot: easy to say that the supply mods are no big deal if you have not tried them out. The choke mod makes sence and it works. I am told that the quality of choke used will have a substantial impact on the results. This makes sence also as wider bandwith will damp diaphragm modulation over a wider range. The mod gives the speakers a real boost in terms of dynamic impact and punch. This is something that others have for years tried to do with EQ. The real solution to the problem is to use no insulation on the stators. Mike Wright had this in mind with his gass filled panels.
I hear what you are saying and I appreciate it. I would love to have the kind of technical background that you have. I think though that you are getting needlessly bent out of shape about the supply experiments. The time frame has not been years, months perhaps but that is due more to my own lack of organization and other factors. This mod is a pretty big improvement in the performance of the system. So much so that it makes me want to build non insulated stators to eliminate the issue all together. Please give it a try and tell us what you hear. Sometimes chewing away at the things that you can is the slow way toward improvement. I think that this has been a valid step forward. Best regards Moray James. |
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| I_Forgot |
Moray,
In these very forums there are people who claim they can hear a difference in a circuit's performance when they reverse the direction of a single resistor. Let's carry that sort of thinking through to its logical conclusion.
If the direction of each resistor were audible, and you have an amplifier with 10 reistors in the circuit, how many different combinations of resistors wired "forward" and "reverse" would you have to listen to to find the "best" combination? There are 10 resistors that can each be put in either of two ways in the circuit, so there are 2^10 unique arrangements (that's 1024). Now lets throw in the claims by many of the same people that a Vishay resistor sounds better here, a Caddock sounds better there, a carbon comp resistor sounds better over there, a wirewound resistor sounds best over there, etc. ad nauseum. Now we have 10 resistors in an amplifier, each of which has to be swapped among say 4 types or brands of resistors, and each of which has to also be wired "forward" and "reversed". The number of combinations to test swells to (4*2)^10=1.074x10^9. THAT's a LOT of resistor arrangements to test, and we haven't even thrown the capacitors into the equation yet!
Now let's say that someone actually goes to the trouble of listening to ALL those combinations of resistors in that amplifier and then someone presents a different amplifier circuit to them and says "what should I do with these resistors to make it sound best?". The only possible answer is that every combination of resistor must be tried and listened to.
Of course, this all assumes that the person listening can actually tell a difference between some combinations of all the resistors and ignores any psychological factors affecting their decision making process (a major leap of faith in human capability). We also ignore age related changes in the perceptive abilities of the person doing the listening and in the components themselves during the many, many years that the testing would require.
We therefore conclude that there is no meaningful predictability. How can there be when no one's life is long enough to thoroughly test even a single amplifier?
Now, if you put one guy to work swapping resistors and another to work designing a better amplifier, which path leads to real progress and useful knowledge?
The guy who wants to make real progress makes decisions about when "enough is enough" and moves on.
I made the suggestion about focusing on bigger issues because the path you're pursuing appears (to me, at least) to be as dead an end as swapping the resistors in an amplifier. With so many real deficiencies in ESLs, why pursue the imagined or insignificant ones?
You don't need to be an engineer or physicist to make a real contribution. Real contributions can be made in construction techniques/materials selection/asthetic design and etc., without any engineering knowledge (though it can help here, also).
On the other hand, if you WANT to make a contribution to the engineering end and don't have the necessary education, go get it. ESLs have been around a while and will still be around after you've taken some classes.
Just because you want to hear things that others can't doesn't mean that you can, and just because you think you hear a difference between two resistors doesn't mean there is one. I suggest you have a look at the web linked document in my signature file, below.
TD |
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| paulb |
Moray made a 5-minute tweak that significantly improved reproduction. How can you argue with that? Yes, at some point he or anybody will hit diminishing returns. But the big issues you refer to need a significant amount more investment in time, money, tools etc.
I agree with the "chip away at what you can" approach. |
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| georgehifi |
Adding a choke that has little or no current (pico amps) being pulled through it would be the same as having a length of wire the same as the choke winding (to the corner shop and back) inserted in the same place.
This also goes against the other mod of droping the series resitance because of the extra series resistance the choke has.
So the whole idea is spitting in the face of Ohms Law.
I'm totaly backing the coments made by I_Forgot.
It's all voodoo.
The only mod here that makes any sense is the cap bypass on the power supply
Cheers George |
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| etalon90 |
About the morray mods.
I`ll try it again to see because I didn`t try it correctly the first time
I use the choke in serial with the load resistor. I didn`t put extra caps.
So:CRL-->esl
I`ll try to separate my last caps to form 2.
So: CRCL-->esl
I don`t know if my result will change but a 5 minutes mods won`t kill me:)
And about think that we can`t explain in audio, is there a lot.
-Why a blue led under a CDP improve the sound?
-why a CD demagnetizer improve really the playback even if a CD is made from non magnetic material (epoxy,aluminium,plastic acrylic)
...
regards |
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| noelm |
I replaced the 500 MegOhm resistor with a 20 MOhm one and added a .022uF 6000 volt capacitor to the high voltage circuit in each interface. The change in sound is really nice in terms of clarity, dynamics, and perceived low and high frequency extension. The improvement is 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. They all like it very much.
Like paulb said: "Moray made a 5-minute tweak that significantly improved reproduction. How can you argue with that?"
Please keep at it, Moray. Thanks.
Noel |
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| Robert F |
Hi, my first post here. I was the one responsible for telling Moray James about the choke mod developed by some friends and I for Acoustats. I am gratified that he has been open minded enough to try it and has experienced similar improvements to me.
That said I am disconcerted at the mean spirited not to mention logically tortured arguments raised by people who have not tried it but who feel they have the explanation as to why it can't work...
I am not sure who takes the cake... the fellow who reckons it can't work because of the 'low currents' involved or the one who reckons it is of marginal if any value because Peter Walker didn't do it 30 years ago... oh and it is equated with hearing Resistor directionality in the same breath.
George, how is it that you think that the capacitor bypass mod has some merit on the one hand but that the currents are so low
that the choke cannot work on the other? If there is no current flow there can be no noise induced by the power supply to the diaphram So it follows that the capacitor mod is doing nothing... If we were dealing with perfect components i.e. a 500 meg resistor that is purely resistive then nothing we do on the supply side will make a difference. 500 meg is huge isolation. |
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| georgehifi |
| quote: | Originally posted by Robert F
George, how is it that you think that the capacitor bypass mod has some merit on the one hand but that the currents are so low
that the choke cannot work on the other? If there is no current flow there can be no noise induced by the power supply to the diaphram So it follows that the capacitor mod is doing nothing... If we were dealing with perfect components i.e. a 500 meg resistor that is purely resistive then nothing we do on the supply side will make a difference. 500 meg is huge isolation. |
1 The cap change increases the the charge voltage, hence changes the efficiency, and can only make the pannels more easily start to leak, because a HT cancer track can form quicker with higher voltage
2 Change the 500meg for a lower value and you introduce a constant charge principal, good for leaky pannels or humid conditions, if you hear a difference, your pannels can not be getting to full charge because they are either leaking or you live in Singapore where the humidity sucks the charge off the pannels.
I've owned 1+1`s, 2+2`s, 2`s and my friend has 6's, and unless you own a electrostatic voltmeter you have no idea of the charge state of the pannels, as they all leak now that they are all old, the plastic honeycomb stator suports are getting chalky and absorb moisture and leak from the mounting bolts though the chalky plastic to the conductive coating HT tab. I,ve ground out the cancerouse tracks that forms on many pannels of my own and friends , it's a never ending constant thing to do now that they are old, and it can only get worse they older they are getting.
3 As far as the choke, it's simply Ohms Law, you do'nt argue with it .
Cheers George |
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| Robert F |
Hi, my first post here. I was the one responsible for telling Moray James about the choke mod developed by some friends and I for Acoustats. I am gratified that he has been open minded enough to try it and has experienced similar improvements to us.
That said I am disconcerted at the mean spirited not to mention logically tortured arguments raised by people who have not tried it but who feel they have the explanation as to why it can't work...
I am not sure who takes the cake... the fellow who reckons it can't work because of the 'low currents' involved or the one who reckons it is of marginal if any value because Peter Walker didn't do it 30 years ago... oh and equates the mod with hearing resistor directionality in the same breath.
George, how is it that you think that the capacitor bypass mod has some merit on the one hand but that the currents are so low
that the choke cannot work on the other? If there is no current flow there can be no noise induced by the power supply to the diaphragm So it follows that the capacitor mod is doing nothing... If we were dealing with perfect components i.e. a 500 meg resistor that is purely resistive then nothing we do on the supply side will make a difference. 500 meg is huge isolation. The fact we do hear improvements by lowering supply noise is testament to the fact that the 500meg resistor is anything but perfect. If it were properly spice modelled it would have a decent sized capacitor in parallel to it which essentially bypasses the resistive component at high frequencies thereby providing a nice series feed for noise at high frequencies. So all is not as it seems at first glance.
I think the key to the choke is to look at the speaker in AC not DC terms. Of course there is little DC current flow, but the speaker diaphragm leaks with excursion, the more it approaches the stator the more it leaks, i.e. the leaking is music related. A hypothesis is either that the choke supplies sufficient current to smooth this (so not inconsistant with Moray's theory about the effect of lowering the resistance to 20meg) or that it reduces leakage back through the 500meg resistor to the supply. Either way subjectively the speaker has a much improved bass and lower midrange performance amongst other things to the extent that it evens out the subjective dip in the lower midrange on these speakers which used to remove the chest from male voices. Yes we still have volume and efficiency limitations, but dynamics are improved.
Anyway this post is overly long but hopefully provides some food for thought.
Rob. |
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| Robert F |
Whoops inadvertantly hit send before finishing my post, sorry.
Now George think AC... ohms law works for DC as I have explained but with imperfect components you have reactive components in the mix as I have (tried to) explain. Maybe my theory is wrong who knows but I know what I hear.
Since you have Acoustats give it a go.
Rob. |
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| moray james |
Hi Rob: thanks in public here for bringing this sweet mod to my attention.
There comes a point where the science inside of the box does not answer all the questions that sometimes arise. In the time that it takes to argue that something like the choke mod cannot work it could be tried out to determine if in fact there is something to it. I think that there has to be some level of trust on forums such as these. If someone is sure that an improvement has been made then if that mod flies in the face of science it is probably worth while to give it a try to at least see what is going on. For those with the ability to model then this becomes a great opertunity to perhaps make a step forward in real understanding.
Tinkering around dropped the noise of the high voltage supply by 20 db which is a bonus in my book. Some say that this is a non issue as the supply is already quiet. Well I can hear the effect of minus 20 db can anybody else? Further I do not think that many if any will argue that ESL's sound better when the HV supply is disconnected or turned off. If the supply were perfectly quiet then that would not be the case.
The choke mod works because it damps the modulation of the diaphragm (an AC component) caused by stored charge in the stators dielectric. The big issue is being missed. Most all thought that this amount of diaphragm modulation from the charged stator dielectric was too small to be an issue. However when damped by a choke the improvement is clearly audible.
I was able to experimeent yesterday with the 7 Henry chokes on my buddies 0ne plus 0ne's. I placed both chokes in series to form a 14 Henry choke and ran both panels off the one supply with the 14 Henry choke. There was a small but noticible improvement in the sound. I should think that a composite choke built up from a series of one Henry chokes will yield a wide band low capacitance choke which will sound even better. I plan to try this idea out.
The real issue here is that perhaps we want to build panels with non insulated stator wires or non insulated perf metal. Only in this way will the issue of stator dielectric induced diaphragm modulation be a non issue. This perhaps confirms why Hunt, Janszen and Strickland all believed in a "leaky" dielectric.
I hope that others who have access to some chokes will try this simple and easy mod on thier ESL panel supplies. I am sure that you will be surprised and impressed with the impact of the choke on the high voltage supply. Further if you post here to recount your findings then others who do not believe that this mod really does anything will perhaps take a second look at it. Thanks for reading I hope that some of you try this and report back. Best regards Moray James. |
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| I_Forgot |
I apologize to anyone who feels my comments were "mean-spirited". My intentions were strictly benevolent. I was hoping to steer people's efforts in a direction that might make a more meaningful improvement in ESL performance. Everyone is free to choose where they direct their energy. The time has come for me to redirect mine.
My signature file says all I have left to say about any of this.
Good luck to you all.
I_Forgot |
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| etalon90 |
Hi
I re-try the choke mods. This time I do it correctly and I use 30Henry choke (hammond 157G with about 600 ohms DCR)
I didn' t do comparaison, I only do the mods and listen my system.
From my audio memory (i didn' t listen my system since the last 4 days :bawling: ), it seem to have a difference. the more difference are at high SPL, the bass is more precise and the medium seem to be more comprehensible. I didn' t hear change in treble.
So, I recomment to give the Morray and Robert mods. It take less than five minutes to do and cost next to nothigh (as compare to commercial tweak as main cable)
Regards |
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| moray james |
| Martin: thanks for listening again and also for posting. From what Robert tells me different chokes can make a huge difference. Wide bandwidth low internal capacitance chokes work best. I recently found a surplus shop with one henry chokes at one inch diameter and 3/8 inch thick. A series string of these with each choke twisted 90 degrees to the next should make a fine very low capacitance choke. They are only $1.49 US each. Let us know if you try out any other chokes. Thanks again best regards Moray James. |
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| moray james |
It has just recently been suggested that the impact on the ESL panel when fitted with a choke in the supply is as a result of a resonant circuit being formed by the choke and the capacitance of the panel.
Rob F.'s comments are as follows Well he is certainly wrong about the resonant peak, since the 500meg R
will damp any resonances big time, in fact a 1K resistor would likely be
more than sufficient to do so. In CLC type tube amp power supplies a low
DCR choke can have exactly this resonant effect. I have played lots of
times with different values on Duncan's power supply design program and
higher DCR
or larger capacitance damps any tendency to resonate.
Any comments or ideas out there? What ever the case I just can not see anybody removeing this mod after they install it, it's a keeper in my book. I look forward to some further discussion. Best regards Moray James. |
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| etalon90 |
HI morray
I listened my system for long time yesterday and try several HV bias scheme.
for the choke, I try 3H,7H,30H,150H. (all cheapos hammond iron)
the 150 henry give the best result and it perform even better when used without load resistor at all. (Just an CL)
But after played with choke, I just switch to 25Meg load resistor alone to see wich improvement I gain with the choke...
WOW. the choke give a nice effect (coloration?) on the voice and give some "sparkle" on trebble (not the extreme treble) but scrap the bass. In overall, the resistor sound is better.:eek:
With 5Meg resistor, I nearly reach the voice of the choke but both extreme are not good. 25Meg seem to be the best compromise here sisce it`s a small improvement over my previous 33Meg.
With choke, is there a audible distortion (charge migration?) in very low bass (x<40hz) and I can`t accept this... The resistor didn`t exibit this problem.
Next time, I`ll try to mix resistor and choke to find the best compromise.
I bet that 10Meg+40henry will be a good start.
Keep posted. |
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| etalon90 |
UPDATE
I try several compinaison of choke+resistor this afternoon with mitiged result.
Then, I suddenly remember that I have a pair of gridchoke (with nikel lamination) design for audio in my inventory...
they are 4000 Henry and can`t take any current but I know they are fine for few mA. (I accidently feed about 43mA for 2 minutes without any damage)
So I hooked them on and, and they provide the best overall sound.
that give the beautiful medium of a small choke, the trebble is just fine and the bass didn`t suffer any audible distortion (to me).
I think that 4000H will be very very hard to beat.
The secret is possibly the wide bandwith of an audio product instead of a power supply iron.
Use audio choke and give us some news:cool:
Thanks again Morray and Robert for the idea, I`m glad to have improved my system again...
best wishes
PS the choke are Magenquest BCP16Ni at US$150 per pair. MQ have also a M6 gridchoke that give about 1000Henry and cost about US$100 per pair. |
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| moray james |
| Rob F. has told me time and again that the quality of the choke is very important. High quality wide bandwidth chokes will have verylow internal capacitance. This is achieved useing multiple chamber windings to form the choke. The chokes That Rob uses are six chamber or six section 10 Henry choke. I will be building up some ten section ten Henry chokes built up from ten one Henry chokes that will be oriented such that each choke is at right angles to the next. Will post what I hear as soon as the chokes arrive and I get the chance to try them out. Best regards Moray James. |
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| moray james |
Ron has been kind enough to contribute to this discussion and as I mentioned before believes that the change in the speakers response/performance can be best explained as a result of a resonent circuit being formed by the inductance of the choke and the capacitance of the speaker panel. I have included Ron's comments in hopes of generating further interest and experimentation by others interested. Best regards Moray James.
Hi Moray:
Those 500 Meg ohm resistors are too high to have any effect on the Q of a tuned circuit. Even 10 to 20 Megohms is pretty high. We could do a circuit simulation to show what effect the resistors would have but it maybe just as easy to connect the componets and measure the result.
The resonant frequency of a tuned circuit is equal too:
Fr = (2 * Pi)/(LC)^1/2
Where Fr = the resonant frequency
Pi = 3.1416
L = the circuit inductance
C = the capacity
The term (LC)^1/2 power is actually the square root of the (LC) product.
Hope this helps.
Ron |
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| moray james |
Hi Moray:
The equation in my last e-mail for the resonant frequency is wrong. The following is the correct one.
Fr= 1/((2 * Pi)*(L * C)^1/2)
Sorry about the mix up.
The Q of a tuned circuit is a function of the resistance. Generally it is the resistance of the chokes winding that controls the Q. Adding and external resistor will do the same thing. With that in mind it maybe that the bias resistance of 500 Megohms or the smaller 10 to 20 Megohms may make the circuit a low Q. In effect dampening out the resonant rise of the tuned elements.
That sort of contradicts the statement in my last e-mail but it is a possibility. I would try the choke without the resistor to see what happens. Then add the resistor to see if it changes the Q of the circuit.
Let me know what you find out.
Ron |
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| Brian Beck |
Moray et al,
I wonder if the capacitance across a single large resistor such as your 500MEG might be a factor. Perhaps it provides a leakage path for higher frequency garbage from the high tension P.S. (in effect forming a capacitor divider with the ESL) You might try replacing a single 500MEG resistor with a series string of, say, 22 separate 22MEG resistors, kept spaced apart or oriented in a straight line. Or to replace a single 22MEG resistor, try ten 2.2MEG resistors in series. This will break up capacitances into series elements with much lower total effect. I'd be curious if you hear a similar improvement to the inductor. Just a hunch. I respect what you're hearing, but the prior explanations seem to be grasping at straws to me. |
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| moray james |
| Brian: you are right about the capacitance of the noninductive high Meg ohm resistor. Your solution is exactly what I plan to do. That said the capacitance of a excellent 6 chamber choke like Rob uses or even the ten stage 10 Henry choke that I will be building up (a composite choke made from ten one Henry chokes in series) still will both have more internal capacitance than the noninductive load resistor. So that begs the question what the heck is that choke doing??? While I too thought that the idea of the choke damping out an AC modulation of the diaphragm caused by the capacitance stored in the stators dielectric was a bit of a long shot I find myself wondering if that may in fact just be the real deal. I would love for someone who has practical experience with supplies like this to give us all the definitive answer. I'am all ears and waiting for a better theory to be put forward. All the best for now Moray James. |
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| djmiddelkoop |
Morey, this is all very interesting.
As said before, I also can clearly hear the difference between a 22Mohm resistor and a 150Mohm between the HV and the mylar. However I changed the 22M to 44M to get a tighter low end response.
We must consider the role of the choke together with the capacitance of the speaker itself.
Also, the type of HV powersupply is important.
General there are 2 types:
boosting or cascading the mains frequency to the required HV
or a switching powersupply working at a much higher freq like 20kHz as in some of the Acoustats.
In the last the choke together with the capacitance of the speaker will act as a huge filter to filter out any ripple.
Maybe it's important to mention the type of powersupply your friend has. Just to get a complete picture. |
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| moray james |
DJ: I was not aware that Acoustat built any speakers with switching supplies. Do you know which modles? The 0ne plus 0ne speaakers that my friend has are cascade supplies.
I was able to get the composite ten chamber chokes built up and cryo treated. These are made up of ten one Henry chokes which were surplus. The chokes are one inch diametre and 3/8 inch thick, they are in series spaced apart and each is at 90 degrees to the next. We were running two Hammond seven Henry chokes in series for a total of fourteen Heneries. The new composite chokes at ten Heneries sound better than do the Hammonds.
The unaccepted theory is that the choke damps diaphragm motion (back EMF) that is the result of charge build up in the stator wire dielectric which then modulates the diaphragm. I think that this makes sense since there is no current to speak of coming out of the supply (steady) except when the diaphragm bleeds off some and the supply has to top the diaphragm up. Perhaps you can give this modification a try and let us know what you find. Best regasrds Moray James. |
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| djmiddelkoop |
The switching powersupply can be found in the Spectra models 11 and 1100.
If I correctly understand Moray, you use the choke without any series resistor, and before the choke there is a cap to ground.
In general, how do we use a choke?
1 for reducing ripple , like in a CLC powersupply
2 for smoothing out current , like in LC powersupply
3 as a frequency depended component , like in a speaker crossover filter
Where can we make the link to the results of the choke experiments ?
Number 1 does shure work here due to the high value of the choke :it’s equivalent to a high value series resistor for AC, or ripple voltage. So ripple and mains garbage will be reduced.
Number 2 also works here due to the high value of the choke for AC : it acts as a constant charge to the panel as it’s equivalent to a high value resistor for AC. For DC or very low frequencies <5Hz, the choke is a low value resistor, the value can be measured with your ohm meter.
So it will keep the speaker constant charged. If there is some leakage the charge voltage of the speaker will not drop as with a resistor. Here the low value DC resistance of the choke applies.
Number 3 doesn’t apply here, because of the high value it works at the whole audio spectrum the same.
This explaines why a larger choke sounds better, as larger means it’s equivalent to a higher resistor.
The multi chamber choke works better because of the much lower leak capacitance. This can be seen as a leak C parallel to the choke which wil make it less perfect for AC.
Don’t forget that if the HV is raised most ESL sound more dynamic and better.
This will be also the case with the choke as there is almost no voltage drop, as explained in 2.
Remember that every ESL has some leakage which will cause the bias voltage to drop when a resistor is used.
The back EMF theory can only work for very low frequencies as here the large choke will also act as a big value resistor.
Hope this helps.
D.J. |
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| Robert F |
dj Good theory except of course in both my application and in Moray James' the choke follows the high value resistor, in my case 500M! So I am confident in saying low DCR has absolutely nothing to do with the effect we are hearing. Ter is considerable voltage drop over the 500M R and extra DCR wont help. I suspect (know) that the 500 M is not a perfect resistor i.e it is reactive - it has considerable capacitive reactance. So maybe the chokes provide more isolation at high frequencies. That and the fact the panels are drawing current with leakage induced by movement of the diaphragm coupled with the fact that chokes store a charge and therefore supply the current draw are my best guess at the mechanism here... Could be wrong of course!
Regards,
Rob. |
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| djmiddelkoop |
Thanks Rob,
I completely missed the resistor that precedes the choke.
In this case my explanation doesn’t make sense, except for the back EMF.
I can assure you that the capacitive reactance the 500M or any high Meg resistor has, plays no role here. I have quite a lot of these kind of resistors and we are talking picofarads at the most here.
However, I can follow your : | quote: | | the fact the panels are drawing current with leakage induced by movement of the diaphragm coupled with the fact that chokes store a charge and therefore supply the current draw are my best guess at the mechanism here... |
This does make sense and could very well explain the experiments.
DJ |
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| Brian Beck |
| quote: | | I can assure you that the capacitive reactance the 500M or any high Meg resistor has, plays no role here. I have quite a lot of these kind of resistors and we are talking picofarads at the most here. |
I must respectfully disagree here. The high voltage side (secondary circuit) of an ESL is an extremely high impedance environment, possibly higher than any other we are accustomed to. Voltages are very high, currents are miniscule and we’re talking about tens or even hundreds of mega-ohms either in the series resistor or on the diaphragm itself. Therefore picofarads DO matter.
If you happened to have 2pF of shunt capacitance across the large value supply resistor, there would be about 4 mega-ohms of capacitive reactance across that resistor at the upper end of the audio band. Whether that resistor is 20M, 100M or 500M, the admittance of that shunt cap swamps the conductance of this resistor. Now, the shunt C may even be larger than 2pF, and I’ve also ignored stray C to the nearby chassis.
My struggle with the choke idea (and I’m not discounting people’s listening impressions one bit) is that a perfect 10 Henry choke in series with said resistor will only exhibit 1.25M of reactive impedance at 20KHz, and lower below that frequency, even if it were a perfect inductor (no shunt C in itself). At 20 KHz the combined complex impedance of a perfect 20M resistor and a perfect 10H choke has an impedance magnitude of 20.04M, almost imperceptibly more than the 20M resistor. Let’s try a 10H in series with a 500M resistor – that gives a magnitude of impedance of 500.0015M. See my point? The magnetically-stored choke energy must be irrelevant since its only effect is this miniscule increase in impedance of the series combination. In either case, the resistor totally swamps the choke in series with it. Now let’s consider a real world choke, even a multi-segment design. It will exhibit many picofarads of shunt C that will drop its 1.25 M reactance to something much lower, making the case even stronger that the resistor will dominate. I don’t what listeners are hearing when they make the choke change, but I’m betting against the series inductance and more inclined to think that shunt C’s matter, although I’m not convinced of any argument at this point. |
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| djmiddelkoop |
Thanks for your thoughts Brian,
indeed you're right, because of the high impedance environment the shunt capacitance cannot be overlooked.
Also your interpretation shows that we are looking at the wrong explanation of what we are hearing.
BTW, I measured the capacitance of some 100M resistors and my meter reads 3pF.
I don't know if this is because of the shunt resistance or the reactance, but it's more than I thought it would be.
Now if powersupply noise is an issue here why do we hear a considerable improvement when the series resistor is made smaller ?
I'm still thinking it has more to do with energy and/or impedance.
I also do not want to discount people’s listening impressions one bit, hey I here it too.
The goal here is to find out what is going on, why are we hearing these effects ?
DJ. |
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| Brian Beck |
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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| moray james |
| 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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| Brian Beck |
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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| pforeman |
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.
Thanks
Paul |
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| moray james |
| 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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| pforeman |
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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| pforeman |
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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| pforeman |
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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| Calvin |
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
Calvin |
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| pforeman |
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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| Calvin |
Hi,
the only reason for a good cap to be changed could be that it has developed defects because of wrong design or faulty working conditions. Film caps e.g. that suffered from internal flashovers (overvoltage). If that is not the case, than there is no reason for change.
I´m not familiar with C4C5Itsywitsyteenybeeny... but i assume a schematic would help :rolleyes: . If C4 and C5 are on the primary side (amplifier side) of the audio tranny than there is no need to use 5kV-rated types. 100V types would be ok. If they however are situated on the secondary side (Stator side, HV-signal side) their voltage rating must be high very high (I´d opt for at least 2x p-p signal voltage).
jauu
Calvin |
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| pforeman |
If I wanted to change the signal path capacitors in my 2 +2's with audiophile grade caps, the highest working voltage I've seen are some Hovland's rated at 1200 V. For the .01 uF caps, should I just parallel 5 or six to get to the 5000 V range .
Same with the resistors. I would like to replace them with the best I can get, but don't see the audiophile types for sale in these High voltage ranges.
Paul |
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| Calvin |
Hi,
...to get to the 5000V range......you will have to connect them in series! Paralleling doesn´t increase voltage rating but the capacitance value. Series connecting increases voltage range but decreases the capacitance value. You have to keep in mind that the voltage range may be a specified as DC-value! The AC-value is typically just 1/3 of the DC-value. And if you look at the datasheets You´ll learn that the AC-value is specified for very low frequencies 50Hz/400HZ/1kHz because these caps were often intended for usage in power-management systems. With higher frequencies the voltage rating drops considerably. The WIMA MKP10, 0.01µF is rated at 2500Vdc and 900Vrms (AC). This later calculates to ~2.500Vpp. The value decreases with a constant rate above 2kHz and reaches 90Vrms (250Vpp) at 20kHz. Sounds slightly different, ey? :cool:
Luckily the high frequency content of music decreases too, but if you happen to test with higher power and a white noise signal -which You find on basically each and every test CD- you very probably blow the caps! With regard to this I wouldn´t trust the info on the izzywizzy site that just one cap with a 5000V rating (AC? DC?) will work reliably (I´ve got the impression that they don´t know exactly what they are dealing with anyway, since their parts choice looks rather like a try-and-error game than solid engineering)
You will rather need a string of series connected caps or a specialized HighVoltage cap with ~20kV rating. Series connected WIMA MKP10 or FKP1 will be very ok, as well as competitor´s caps in a comparable build and with comparable specs.
This only relates to C4 and C5 which must have high voltage ratings!
If the maximum signal voltage is far below 100V -as it is the fact for all the other caps- it is utterly nonsense and a lot of wasted money to use vastly voltage overrated caps!! :rolleyes:
High voltage rating with capacitors just makes them big and expensive, not better. But in the end that´s what the HighEnder wants.....impressive, vastly oversized and preferably terribly costly looking stuff! Should it come out that its crappy stuff, don´t worry. Just tell everybody that it´s sounding better than You´ve ever heard before.
"Audio Grade" is only a marketing term but implies a superior quality of such a part over ´standard´parts. It also seems to imply that this part is superior in any case, regardless of its position within a circuit. This simply does not hold true! Since the demands of Audio are fairly low compared to other technical areas the so called ´Audio Grade´parts don´t need to be high quality in a technical sense. Just think of carbon resistors, oil-filled caps, electrolytics and especially some cables which are grossly inferior to standard parts.
The claimed superiority only relates to unmeasurable parameters like sonic behaviour. And that is a subjective and very debatable parameter.
So, apart from C4 and C5 all other caps in the circuit may happily be specified far below the kV-range.
For R2 and R3 (HV-Side) noninductive wound wire resistances are ok
Similar to the caps it may be necessary or even needed to series connect a couple of resistors. I wouldn´t use thickfilm resistors here and the probabely best Rs -made from metal foil- will be very expensive
On the lowvoltage side R1 and R4 can be of Metal foil build. The probabely best resistors here are the Isabellenhuette PBH and PBV and PSB. http://www.isabellenhuette.de
The HV-resistor R5 can be made from a chain of metal film resistors (0.5-0.6W, 1%-5%, size 0207). They are spec´d around 250V-300V, but in practise use them not above ~150V. For 5kV bias you need app 30pcs of 1MegOhm.
The original value of 500Megs is much higher than I´d use if a high ohmic coating is used on the diaphragm. 50Megs at maximum. You should be careful not to touch any HV-point, since the smaller resistance means higher currents and therefore more pain when getting shocked. ;)
If someone reports sonic differences because of using a different resistor for R5 of same value, I´d say this would rather be a hint that the circuit itself is of minor design quality or psychology is playing games on him.
I´d rather make the HV stiffer by using larger Cap-values for C6 to C10 (>10nF) and use a negative polarity output instead of the positive. And adding a blinker cicuit (see Quad) will isolate the HV from the membrane.
The 10nF cap directly at the output of the cascade does no good. If you feel the need -a need that is actually nonexistent in praxis- that you have to smooth out the output than add a series resistor of 10M between output und 10nF-cap.
I don´t believe that a inductor could do anything positive here. The series resistance of R5 added to the high resistance value of the membrane coating works as ripple and noise filter already.
Besides the restrictions Mr. Beck mentioned (though I don´t see ´noise signals´ of sufficiently high frequency anyway) we are talking here about microscopically small currents. Which leads to the Q: If there were any ripple and noise above 100/120Hz.....would it supply for enough current in the inductor to make any difference to a resistor of same DC-ohmic-value? Or in other words:" Does the inductor work as inductor, or merely like a low-ohmic wire wound resistor?" Replacing R5 alltogether by a inductor shouldn´t be done because of safety reasons (current limiter).
jauu
Calvin |
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| pforeman |
Hi thanks again for your help.
I think I've found the parts I want to get.
The closest I've found for the 5000V ..01 uF is a 6000V (went over instead of under Voltage) .0047 uF. Polypropylene isnt available in this high of a voltage, but polyester is. Are either or both of these changes ok?
Also, the high frequency caps in the manual are 220uF,10uF, and .01uF.
I've seen in this forum to replace them with 50uF Blackgate, which I understand are discontinued. I have medallian and C updates. What values are people recommending.
Thanks again,
Paul |
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| stokessd |
Where are the measurements folks?!
I_Forgot did what folks should do, which is to use circuit theory to help guide the design process. The next step is to make the change guided by the math and then measure the change. Lets for a moment believe that the the choke and the cap before it made a difference, then that difference should be measurable. If you don't have the tools to measure it, then how to you know that you actually improved it? Ears are hardly reliable. And how do you optimize the change? Is 7H the right number? How about 5 or 10?
So until there are actual measurements, my advise is to stick with the stock acustat circuit.
Also 405man is right, the neon bulb circuit isn't my design, it's been around for decades.
Sheldon |
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| bentoronto |
Measurements... right!
You can make a string of HV high resistance resistors (say, 10 50-meg-ohm units from your local surplus place) and maybe a 10 meg resistor on the bottom. Then you can read proportional AC and DC voltages or 'scope the signal off the bottom resistor (the one with one end attached to ground, that is).
Glad to see that some sound back-of-the-envelope electrical judgment made the silly choke idea go poof.
The izzy wizzy HV cap, on the other hand, raises the bias supply. Which makes ESLs louder and hence sound better (until you put the SPL back for a fair A-B comparison and then they might sound the same).
Don't forget the old rule for working around HV: always keep one hand in your pocket. |
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| Robert F |
Except Bent, the "silly choke" idea is anything but silly when you hear the effect.... It is not a subtle change at all, and no I am not hearing things. Your back of the envelope may disagree which is its privilege.
Regards,
Rob. |
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| stokessd |
I'm not going to discount your listening experience, but how do you design anything using your ears?
Electrically the choke is meaningless, so how do select the correct value, and how do you know that your "different" is "better"?
Sheldon |
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| moray james |
but it can be done, has been done and is done. Kind of like paint by numbers without the numbers. Difficult yes that goes without saying but it is done. The best of all worlds is (I think) when both measurements and listening are used together as long as the ears have veto power. All the great masters built their instruments with their ears and their hands. That tradition holds to todays best as well.
Lets face it you can find good examples of both methods and this is not about right or wrong. Either method can suggest experimentation be done as long as the ears rule the day I dont think you can go wrong. You know what happens when the "bean counters" start to tell the engineers how to design a bridge. |
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| Robert F |
| quote: | Originally posted by stokessd
I'm not going to discount your listening experience, but how do you design anything using your ears?
Electrically the choke is meaningless, so how do select the correct value, and how do you know that your "different" is "better"?
Sheldon |
Sheldon, I agree in terms of designing anything that measurements have to be used to get in the ballpark so to speak. However, In this case I agree that I cannot think of a mechanism explaining what I hear. I had it demonstrated to me (blind) in a friends system and it is very obvious.
That said, it is easy to decide whether different is better if you live with the change for a while, and IMO making a good design better requires the use of the ears.
Rob. |
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| arend-jan |
So who's going to do a couple of measurements to find out what the change entails?
Without understanding there can be no real progress. |
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