Hi,
You can´t tell the transformation-ratio by the coils (DC-)impedances, since the ohmic (DC-) value depends on the length of the wire, the material and the gauge.
You have to measure the voltages for a given frequency (start with 1kHz).
The wattage You need depends on what kind of ESL You want to drive. For a fullrange ESL 100W is ok, for a hybrid-Type working from 100Hz or above, smaller types are useful.
If You really need a powersupply that delivers 10kV, I´d rethink about the ESL alltogether. Tubeamp-trannies are not designed to withstand such high voltages and would soon fail because of internal flash-overs.
The formula for the voltage -even though formally correct- doesn´t apply here. The output voltage of the amp (40V in this example) is measured as a rms-value, but we need peak-values here.
40Vpk~28Vrms --> 1:250 for 10kV ...or...40Vrms~56Vpk -->1:180 for 10kV.
Still both numbers are much higher than with any tubeamp-tranny.
Additionally such high figures present the tranny-designer with serious problems and the driving amp with ridicoulosly dangerous impedances. Bandwidth will come down considerably, as well as safety....and uhhh... btw.... it doesn´t sound good either ;-)
jauu
Calvin
You can´t tell the transformation-ratio by the coils (DC-)impedances, since the ohmic (DC-) value depends on the length of the wire, the material and the gauge.
You have to measure the voltages for a given frequency (start with 1kHz).
The wattage You need depends on what kind of ESL You want to drive. For a fullrange ESL 100W is ok, for a hybrid-Type working from 100Hz or above, smaller types are useful.
If You really need a powersupply that delivers 10kV, I´d rethink about the ESL alltogether. Tubeamp-trannies are not designed to withstand such high voltages and would soon fail because of internal flash-overs.
The formula for the voltage -even though formally correct- doesn´t apply here. The output voltage of the amp (40V in this example) is measured as a rms-value, but we need peak-values here.
40Vpk~28Vrms --> 1:250 for 10kV ...or...40Vrms~56Vpk -->1:180 for 10kV.
Still both numbers are much higher than with any tubeamp-tranny.
Additionally such high figures present the tranny-designer with serious problems and the driving amp with ridicoulosly dangerous impedances. Bandwidth will come down considerably, as well as safety....and uhhh... btw.... it doesn´t sound good either ;-)
jauu
Calvin
With a small risk to personal safety (zero if you're a careful sort), you can get that ratio at 50/60Hz. Measure mains voltage. Then connect your meter across the lower voltage winding of the candidate transformer. Connect the mains across the higher voltage winding, then note the meter reading. Turn ratio is the ratio of mains voltage to outputvoltage. Simple, eh?
With a tube output transformer you can also calculate stepup using
N = Squareroot (Zprim/Zsec)
Zprim and Zsec are the values provided by the manufacturer, NOT the DC-resistances of the windings!
So if you have an output trannie spec'd at 6kOhm / 4Ohm, it has a stepup of 1:39. You'll find it very difficult to find a tube trannie with a stepup >1:50...60.
I fully agree with Calvin about the problems using 10 kV and high stepups. Better rethink your design, reduce spacing, maybe increase surface, try to keep bias < 5kV and stepup < 1:150.
If you have acces to one, better use a sine wave generator to put around 1 V over the primary, then measure Vsec.
N = Squareroot (Zprim/Zsec)
Zprim and Zsec are the values provided by the manufacturer, NOT the DC-resistances of the windings!
So if you have an output trannie spec'd at 6kOhm / 4Ohm, it has a stepup of 1:39. You'll find it very difficult to find a tube trannie with a stepup >1:50...60.
I fully agree with Calvin about the problems using 10 kV and high stepups. Better rethink your design, reduce spacing, maybe increase surface, try to keep bias < 5kV and stepup < 1:150.
If you have acces to one, better use a sine wave generator to put around 1 V over the primary, then measure Vsec.
100W transformers are going to be huge, and very expensive, and completely unnecessary. A 30W transformer is sufficient. Audio transformer power ratings are a spec that is dictated by the marketing dept. A transformer rated for 30W at 20 or 30 Hz will be rated for 100W at 250 Hz. When comparing audio transformers the weight is often the best clue to see which can really handle power because most of the weight is the core and core size is the main factor in determining the power handling.
As previous posters have said, the enormous transformation ratios you are looking for are not easy to find. You can make life easier if you use two transformers per speaker.
I have not yet tried it myself, but other posters on this forum claim to have excellent results using toroidal power transformers for the audio. You can get surplus troidal power transformers for $5-20 each. The low voltage winding doesn't matter much- what you're after is the core and the dual 115V windings. Look for low voltage secondaries, but if you can't find anything less than 12-24V it doesn't matter because you can either remove some of the wire or just add your own winding (as long as the core isn't potted).
Here is one that is much largr than needed:
http://www.alltronics.com/cgi-bin/item/24E017/E/Toroid-transformer-multi-output
Here's one that a more reasonable size (and price) but will require either unwinding the secondary, or adding your own (just a few turns of wire):
http://www.halted.com/commerce/ccp20783-toroidal-transformer-70-vct-20691.htm
Here is one that looks good, but has only one 117V winding.
http://www.herbach.com/Merchant2/me...AR&Product_Code=TM00XFR4409&Category_Code=XFR
Here's yet another:
http://www.electronicsurplus.com/commerce/ccp91231-toroidal-transformer-462380000-147820.htm
You can get 4 surplus power transformers for less than the price of one audio specific transformer.
I_F
As previous posters have said, the enormous transformation ratios you are looking for are not easy to find. You can make life easier if you use two transformers per speaker.
I have not yet tried it myself, but other posters on this forum claim to have excellent results using toroidal power transformers for the audio. You can get surplus troidal power transformers for $5-20 each. The low voltage winding doesn't matter much- what you're after is the core and the dual 115V windings. Look for low voltage secondaries, but if you can't find anything less than 12-24V it doesn't matter because you can either remove some of the wire or just add your own winding (as long as the core isn't potted).
Here is one that is much largr than needed:
http://www.alltronics.com/cgi-bin/item/24E017/E/Toroid-transformer-multi-output
Here's one that a more reasonable size (and price) but will require either unwinding the secondary, or adding your own (just a few turns of wire):
http://www.halted.com/commerce/ccp20783-toroidal-transformer-70-vct-20691.htm
Here is one that looks good, but has only one 117V winding.
http://www.herbach.com/Merchant2/me...AR&Product_Code=TM00XFR4409&Category_Code=XFR
Here's yet another:
http://www.electronicsurplus.com/commerce/ccp91231-toroidal-transformer-462380000-147820.htm
You can get 4 surplus power transformers for less than the price of one audio specific transformer.
I_F
ak_47_boy said:
A driver needs either a transformer with a center tapped winding or two transformers with the windings wired in series, thus creating a center tap.
It is hard to get huge transformation ratios in a single transformer, so using two transformers will enable a higher transformation ratio. Also, when using two transformers, you can use a smaller core than when you use a single transformer.
If you want to triamp the system, you will need at least 3 transformers or as many as six per speaker.
The voltage transformation ratio for audio transformers requires that you take the square root of the winding impedance ratio. For power transformers the voltage transformation ratio is simply volts out / volts in. A 120VAC to 12VAC transformer has a 10:1 voltage transformation ratio when used to drive an ESL. If that transformer has dual 120VAC windings, as many do, you can get 20:1 from it.
Toroidal transformers that are not potted (embedded in plastic) are easy to change. All you have to do is wrap a few turns of wire over the core and you can get just about any transformation ratio you want.
Since you are asking these basic questions I assume you have not built an ESL yet. I would advise against planning a triamped design as a first undertaking. Build a few small test drivers, use one or two transformers to drive them and see how you like them. ESLs are very wide bandwidth drivers. They don't require a lot of complex crossovers and multiple drivers to get them to sound good. Very complicated, expensive projects are the type that get started and never finished. Start simple and cheap and your results will inspire you to build on your successes. Almost all the parts you use to make a small driver/system are reusable in a bigger system, so nothing will be wasted.
I_F
Hi,
maybe just to get some things clearer for You.
The Bias voltage and the trasformation factor have nothing to do with each other in first case! You don´t design the transformer ratio after some DC-Voltage on the diaphragm, but solely for good efficiency and based on the geometrical and electrical design of the panel.
Regarding this it should be Your aim to design the panel such that the transformer ratio could be as low as possible. I prefer to stay well below 1:100 since as a result these designs sound better, have greater dynamics and play safer.
jauu
Calvin
maybe just to get some things clearer for You.
The Bias voltage and the trasformation factor have nothing to do with each other in first case! You don´t design the transformer ratio after some DC-Voltage on the diaphragm, but solely for good efficiency and based on the geometrical and electrical design of the panel.
Regarding this it should be Your aim to design the panel such that the transformer ratio could be as low as possible. I prefer to stay well below 1:100 since as a result these designs sound better, have greater dynamics and play safer.
jauu
Calvin
Ahhh i see.
I am trying to make some small esl's now. I have run into a problem, i am useing a ac adapter tranformer backwards and a voltage multipler as a bias. The secondary windings on my tansformer read 2 ohms. I have another ac adapter and the secondary also reads 2 ohms. The primarys are 2kohm. When i try to power it up my 5 amp fuse blows, i try to add resistors in line to bring the resistance down and the resistors burn up. What is going on?
I am trying to make some small esl's now. I have run into a problem, i am useing a ac adapter tranformer backwards and a voltage multipler as a bias. The secondary windings on my tansformer read 2 ohms. I have another ac adapter and the secondary also reads 2 ohms. The primarys are 2kohm. When i try to power it up my 5 amp fuse blows, i try to add resistors in line to bring the resistance down and the resistors burn up. What is going on?
Hi, ak.
Where is your fuse wired in? If you can give us a diagram of your wiring, we should be able to help.
Here's a diagram from Mark Rehorst's web site that shows how to connect the parts if you have a center tapped step up transformer.
Where is your fuse wired in? If you can give us a diagram of your wiring, we should be able to help.
Here's a diagram from Mark Rehorst's web site that shows how to connect the parts if you have a center tapped step up transformer.
An externally hosted image should be here but it was not working when we last tested it.
ak_47_boy said:
If you use your ac adapter backwards, you are connecting the secondary to the mains? That doesn't work, the current from the mains into the secondary is too high. If the fuse wouldn't blow, the adapter would! That transformer never was designed to take a magnetic flux that is an order of magnitude higher than normal. The core saturates which drops its impedance for the mains current to almost zero (or the wire impdance of 2 ohms in this case).
You can probably use a normal adapter of say 24V sec, and then a second one say 12 to 120 (or 220 if you are in europe) connected sec to sec, so at the end you end up with several 100 V, isolated, and then try your multiplier.
Jan Didden
In theory: Yes. But if you plan on building a next project afterwards, I suggest you try to survive this one...
So for safety reasons, use two transformers connected back-to-back:
T1: 120v>xxV
T2: xxV>120V > feed that into your doubler
You don't need any power, a set of 1 or 2 VA trannies will do. Sec voltage (xx) is unimportant either, as long as both transformers are equal. Such small trannies are cheap. Don't try saving 5$ here, don't mess with mains if you don't have to.
Also don't get tempted to feed say 12V form a 120/12 into a 6/120 to get 240V out. It won't work. As a rule of thumb, a power transformer's core will saturate about 20% over it's rated voltages. Cores are expensive, you can count on it that the manufacturers squeeze the max out of them.
Also don't forget to place a resistor of 22..100MOhms in series with the doubler output, to limit the current.
ak_47_boy said:
What counts is the amount of flux generated in the core. All depends on # of windings and frequency divided by core area (what matters is the flux density).
When the flux density hits the ceiling (around 1.5T for iron) the windings lose their inductance, all that remains is the DC-resistance. And 2 ohms over 120V will try to draw 60 amps ...
It's a good thing to have fuses
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