# Designing an output transformer using a power toroidal transformer

#### Chace

Hello.
I tried to purchase a commercially available product as an output transformer to operate a full-range ESL, but I was hesitant because it was expensive.
Please tell me how to design an output transformer that uses a toroidal transformer for power supply and what precautions should be taken.
It may be easy for those who are familiar with electricity. I felt it was difficult to trade off in various aspects.

That's my understanding for now.
As a basic usage, the primary and secondary are reversed from the original usage of the power supply toroidal transformer.
When using a 50VA 230V/6Vx2 transformer for each of the front and rear stators, the calculation is about 1:76.

Are there any common transformer combinations that you can say, "I can't go wrong with this set"?
What are the transformer specifications, usable capacitance, and maximum input?
For full range:
For treble:
For base:

By using 4 or 6 transformers, using the LV side in parallel and the HV side in series, you can boost the voltage even higher. Does the number of transformers increase the corresponding capacitance?

Is the approximate corresponding capacitance determined from the combination of transformers used?

What is the allowable turns ratio? Up to 1:120? What kind of problems will occur if it is exceeded?
Can you calculate the frequency to roll off? Are there any problems with low frequencies?

Can a transformer whose dielectric strength is unknown be used as an output transformer? Are there required safety standards?

It is not the case that the higher the rated power, the better. Is there a standard for selecting the rated power of the transformer?

#### boyfarrell

First you need to specify your targets:
1. Primary impedance
2. Secondary impedance
3. VA rating (Watts)
4. Low frequency cut-off (-3dB frequency)
5. High frequency cut-off (-3dB frequency)

It’s a complicated iterative process.

#### mattstat

1:150 turns ratio is about the upper limit of off-the-shelf transformers if you want wide bandwidth, even with multiple transformers driven in a series/parallel configuration. A segmented panel is also necessary in many cases to limit the load at high frequencies. Most of my experience with this approach was using Hammond tube output transformers. They've also gotten more expensive over the years, but I'm not sure what kind of price tag scares you

If trying to do a full-range panel with high drive level, toroidal transformers don't don't handle bass as well as EI. My experience here was with Plitrons vs. Hammonds and Tranex.

There are some users here that are very versed in transformer specifics. Some log-in a little infrequently though, so you may need to give it some time. There are also several threads with discussions about transformers. Here are a few to get you started:

https://www.diyaudio.com/community/...mer-for-step-up-measurements-part-1-2.202638/

#### JMFahey

I tried to purchase a commercially available product as an output transformer to operate a full-range ESL, but I was hesitant because it was expensive.
Please tell me how to design an output transformer that uses a toroidal transformer for power supply
There is a reason behind high price, don´t you think? .... absolutely different beasts.

Power transformers are excellent as OTs .... if you stick to 50-60Hz only, and to boot you drive them from a very low impedance (such as Mains line).

Too low inductance so too low impedance at low frequencies, forget driving them from tubes and expecting any Bass.
At the same time, internal parasitic inductance will murder highs.

#### sonomanie

search for CharlieM on this forum, he uses power transformers for his exellent electrostatics

#### Chace

I searched and read the past diyaudio logs in my own way, but the content was case-by-case, and I didn't get a solid understanding.
Personally, I hoped that it would be easier for people like me, who have little knowledge of electricity, to have more comprehensive information.

to Mr. boyfarrell
You didn't write the details of the ESL you were aiming for, which makes your question vague.

to Mr. Mattstat
I see, the transformer turns ratio is less than 1:150.
The price of the output transformer is what I personally felt when I saw ER Audio.
Considered again.The full-range ESL element I am currently trying to make is 1650mmx163mm, d/s=2.7mm, 0.88nF. I plan to use the electrical segment.
However, in the future, we are also thinking about physically separated segments of 2-way or 3-way.
This question has become a broad question.
I will read the URL you gave me.

to Mr. JMFahey
I think so.
The output transformer on the market is assumed to be used for ESL, and it is guaranteed, so I am satisfied with the price.
Since the power transformer is used for unexpected ESL, if the strategy fails, it will be garbage.

to Mr. sonomanie
Mr. CharlieM's "The Jazzman MkIII" design is also good, and I admire it with a wonderful system!

#### maudio

Some 6/230V toroids have excellent bandwidth even for for fullrange use, others don't. The problem is you won't be able to predict this as the manufacturers won't specify this for a power toroid of course. Either wait for someone to tune in that can point you towards a specific type, or just buy one and measure it. If it's fine for your needs, buy the rest. Only transfomers with a single 230V winding will do, forget all with 2x115V windings.

For a fullrange panel you're looking at placing 4 primaries in series per channel at minimum. This setup will saturate at around 4*6 + 10% = 26-27V rms input @ 50Hz. At 30 Hz this will reduce to approx 16V, equivalent to 30W at 8 ohms. That's really the bare minimum you will need for a fullrange esl. With the 4 secundaries in serie as well that will result in an overall stepup of 1:76, which is low and will give very poor sensitivity. Don't expect your esl to play loud with this setup. I would go for 8 per channel doubling stepup.

Consider a (dipole) sub to cross the esl panel over around 100Hz, will make things so much easier for both panel and transformer. Overal sound quality will benefit as well.

#### sonomanie

Is it a good option of using heavier transformers , for example 100 VA because the number of windings is less and the wire thickness is greater which makes the the capacitive coupling and wire resistance smaller.I

#### maudio

The point is that core saturation is a function of Bmax (core material dependent), voltage and frequency. A mains transformer is designed to run close to the saturation point of the core at 50/60Hz and at the rated voltages. A bigger transformer will not allow for more voltage per winding, just more current. A 50VA 6V winding is rated at over 8A, more than sufficient. Keep in mind the average current will be relatively low with music compared to when used as a power transformer, so overheating is not likely to be an issue. In fact when you use 8 trannies in a 4-2 arrangement with 2 sets of 6V in parallel, the current per transformer is halved and even a 20VA would do.

In fact a larger transformer will have more winding area and capacitance and is therefore likely to perform worse when it comes to bandwidth.

1 user

#### Chace

hello maudio.
I see, even toroids with the same specifications have different bandwidths. Differences in core materials have an effect.
I also learned that the rated power of the transformer should not be too high.
I would like to choose the toroidal I actually use by learning how to use it, the manufacturer and model number from successful cases.
Actually, you can't just import anything and get the toroid you want...

I would like to know the reference examples for full range, treble, and bass. I'm sure it will be useful for others besides myself.

My current personal goal is full range, but I'm considering 1:115 using six 230V/12Vx2 50VA.

The area below 100Hz becomes difficult, which is also the reason why we do not recommend full range for DIY.
Do you install a low-cut filter on the ESL side?
If you use filters in general, are they passive? Is it digital such as DCX2496?

#### maudio

Last time I tried 6/230V toroids is over 10 years ago, none of those models is still available. Back then some models were known to be usefull but I could not get those from my suppliers. Must be a thread about it here somewhere which models were ok. I tried two models and wasn't too excited about the results and ended up buying a commercial ESL model that needed a rebuild. First idea was to pull the transformers for a diy panel but I ended up rebuilding the commercial panels and am still using this ESL (Audiostatic).

I use a 3rd order 100Hz highpass filter on my ESL combined with a tuneable notch filter to suppress the ESL resonance which is around 40-50Hz, and a correction for the dipole cancellation that starts around 300 Hz. All analog active filters, seperate amps for ESL and subs. Nowadays I think I would choose a minidsp or so for the filtering, easier and more flexibility.

Last edited:

#### Chace

You may need to import it yourself, or it may be difficult to obtain.
More often than not, you don't get the toroidal you want.

There are almost no ESL step-up transformers on the market, right?
You don't sell amplimo or Audio4 now, do you?
I only know ER Audio sells them.

I often see examples of "VTX-146-050-106" made by MULTICOMP, so it may be good.

I have been trying for over 10 years. wonderful.
I would like to acquire the knowledge to be able to select parts by my own judgment like Mr.maudio.

I also have an Audiostatic DCI whose diaphragm film has become unusable.
It may be quicker to fix this.
For now, I have a strong desire to build my own.
I will try to move forward little by little.

#### golfnut

If you are using commercial toroidal transformers

The for non-segmented panels use a largish transformers - minimum of 50VA - rating to minimise the transformer inductance. Maximum step up ratio is about 60-80 for a large fullrange ESL, you can get more for a smaller panel. All of the commercial ESL transformers I've seen specs for are designed for these ESLs.

For segmented panels (using resistors between the segments), I've found that 15 VA torids are fine and much cheaper - they balance capacitance and inductance quite well. Maximum step up ratio for a full range segmented ESL is about 120-140.

In either case, get them with a SINGLE !!!! 230 V primary winding, or a single 115 V primary winding.

Do not buy Multicomp transformers, they have two 115 V primary windings and have a high capacitance and limit the bandwidth.

In either case, to get the step-up ratio and the input voltage rating you want put the 230 V windings in series as the output. Then series and parallel the low voltage winding to get the input rating you require.

For example 12V:230V 50 Hz transformers have a step up ratio close to 20. So for a 1:120 step up overall you need 6 transformers (3 each side of the HT) with all of the 12 V windings in parallel. The 12V rms will allow for ~18V peak at 50Hz, 36 V at 100 Hz (proportional to frequency). If you require ~1:120 with 24V rms input rating, use 12 transformers with 24V rating with the low voltage windings in parallel.

Happy hunting

1 user

#### maudio

Or wind your own, if you can find some decent cores and you have generous amounts of spare time You want to minimize capacitance and leakage inductance, which is quite a challenge ad the requirements contradict. More interleaving of windings gives lower leakage but higher capacitance. In general it's a balancing act that might take some trial and error. Ideal are large C-cores because they allow splitting the windings in two coils on the same core, plus they offer long bobbin length so you can minimize the number of wire layers. Choose the core as large as possible, limiting factor being the minimum number of primary turns required for sufficient inductance for the lowest frequency you aim for. Use lots of insulation between each layer of primary windings.