High Voltage Bias for DIY Electrostatics

[Petter]

You cannot wire a step down transformer backwards, and it is not usually the voltage rating that gets you. What happens when you up the voltage is that you get too much flux and thus saturation of the BH curve. This is the same as a short circuit.

Petter

[phishead8]

Hmmm...
People claim that using a step-down transformer backwards is a solution. Not just HifiZen, but Roger Sanders. Are they using a different type of transformer? Larger, more robust ones? My transformer looks about the size of the one that Barry Waldron sells on the Electrostatic Exchange. I haven't heard of the problem of saturation of the BH curve (whatever that is) before. The only thing that I do know is that my transformer couldn't take line voltage. Perhaps I am witness to this problem first hand.
Once again, I am left in the dark without a high voltage power supply.
Any help will be greatly appreciated.
-Dan

[GRollins]

I don't normally disagree with Petter, so let me try to catch up on this thread (been writing and working on tube phono stage--not enough hours in the day to do all this fun stuff)...
Dan,
Let me verify what's going on.
You're running a smallish power transformer "backwards." It has dual primaries and dual secondaries (now being reversed). When you hook it up, it starts grunting and huffing and smoking.
Hmmm...
Two things occur to me:
1) Are these transformers new or used? If new, that's one thing, but if used...
2) I'm thinking that there's a fairly strong possibility that you've got the windings hooked up funny, and that's what's giving you fits.
Petter's point about the flux saturating the core doesn't ring true for me (based on what I think I know--somebody correct me if I've misunderstood). The flux in a transformer is going to be proportional to the load. Since, in this case, the secondary (erstwhile primary) is open (Yes? A meter doesn't count, since it's going to be a skillion ohms going in the front end.), the reflected impedance back though the primary (formerly the secondary) is also going to be nigh onto infinite. Hence there's not a significant current drawn and the flux is going to be very, very low, although not zero. I find it difficult to envision the transformer core saturating under these conditions.
Besides, I've run transformers backwards before.

Grey

[phishead8]

These transformers came out of apparently unopened boxes. I got them off of Ebay though, so one never knows...

Looking at the website specs : http://www.hammondmfg.com/160.htm , I see a possible problem. I shorted 6 and 7 and hooked up 5 and 8 to line. Simply because it was easier to do.
Should I hook up the hot lead to 5 and 7 and the neutral to 6 and 8? Or is this the wrong connection. I am pretty baffled here.
Well, I still have four to play with.
-Dan

[phishead8]

I think that I've found a solution.
I consulted the local electronics expert. He guessed that the reason that the transformer blew was because of shorting inside of the transformer. The side that was designed for 24 volts may not enjoy 110. Likewise for 110 and ~450. Hence, shorting and current draw, resulting in violent buzzing and smoke. He did, however, offer a solution to my problem. He suggested that I hookup all four transformers in series, but still as step up transformers. That way, each transformer only sees 28 volts, well within spec. Then, I merely hook up two transformer's secondaries in series, and I can graciously receive my 450+ volts.
The only problem that I have now, is that I would like to build 2 bias supplies. Since I have 4 transformers and I'm only using the ouput of two of them, it seems to me that I can work it out. The other two transformers are acting only as inductors. Perhaps, I can replace them with an inductor and save myself from buying 4 more transformers for the second supply.
Basically, I need to drop the voltage out of the wall by half and a resistor might get too hot. I am trying to do this without buying another step down transformer, but I may have to. My local expert has dissappeared for a couple of days before I could ask him about it, so any input is appreciated.
Thanks
-Dan

[william2001]

Don't mean to be a pain but I think you could save yourself alot of trouble just getting one of Barry's transformers, and hang your diode/cap ladder off it. Shouldn't cost much, has a primary rated for AC line voltage, gives you the ~500V steps, small size, etc. (I originally wanted to just hook one up backwards too). To fine tune the voltage, I use a simple voltage divider on the primary with a couple of high wattage Ohmite resistors, one has the adjustable tap. Not elegant, but works great!

[phishead8]

William,
I am very close to completing the high voltage bias supply with my own transformers. I have plenty of time to play with this stuff while I'm waiting on parts for my next set of electrostatics. I'm also making a pair as a gift. I'm pretty stubborn and want to try and finish this stuff with the things that I already have. I don't want to sink any more money than I have to into this project. Besides, it's a learning experience for me. But, if I cant get it to work I'll just buy Barry's supply.
Thanks everyone for your input.
-Dan

[william2001]

That's cool, I can certainly understand not wanting to spend more money if you don't need to. (I seem to have a knack for making bonehead mistakes, and learning everything the hard way....). I certainly "learned alot" with my DIY ESL project, HA! I hope you let us know how everything turns out, and your impressions of the sound quality.

[CharlieM]

Originally Posted by phishead8

William,
I am very close to completing the high voltage bias supply with my own transformers. I have plenty of time to play with this stuff while I'm waiting on parts for my next set of electrostatics. I'm also making a pair as a gift. I'm pretty stubborn and want to try and finish this stuff with the things that I already have. I don't want to sink any more money than I have to into this project. Besides, it's a learning experience for me. But, if I cant get it to work I'll just buy Barry's supply.
Thanks everyone for your input.
-Dan

I guess I'm a little late for the dance here but if you're still looking for a cheap, effective power supply, you could build a pair (2) like mine for about $50 in parts. They're configured for 1/16" stator-to-diaphragm spacing so you would need a higher output supply for larger d/s spacings. There is a parts list and schematic posted on my blog page here: The Jazzman's Electrostatic Loudspeaker Page

[kavermei]

It's an old thread, but allow me to present my solution to you all.

I bought a 'cold cathode fluorescent lamp', or CCFL, the type of colored tubular lamp that kids put inside their computers to show off. They are dirt cheap, maybe $8. Those lamps need a high AC voltage, so each set contains a little resonant inverter, a small 1x3" box you can tuck away anywhere.

All you need then is just a short voltage multiplication ladder, and a series resistor. The inverters I have run at around 52kHz (43kHz loaded), so you can use tiny capacitors in the ladder -- I used 4.7pF 2kV, which are waaaay cheaper than what you need for 100 or 120Hz.

The inverters run off 12VDC, of course. Want to adjust the high voltage? No problem, just put a LM317 in front! My panels start to hiss at a supply voltage of around 5V.

Small, light, cheap, buy anywhere, adjustable, ho hum, ... It just doesn't get any better than this! And you can even pimp your speaker by putting the lamps in!

Kenneth