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Old 17th August 2012, 09:01 PM   #1
fperra is offline fperra  United States
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I've posted my ESL build in another thread but I thought I'd start a new one concerning transformers. I'm still searching for a good, reasonably priced transformer to drive my woofer panels up to about 400Hz. I recently came across these and wonder what the transformer experts think?

Transformer - Hammond, Output, Push-Pull, 100 W | Antique Electronic Supply LLC

I could use two of these in series/parallel if one wouldn't work.

Last edited by fperra; 17th August 2012 at 09:36 PM.
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Old 18th August 2012, 01:35 AM   #2
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Using the 4 ohm tap the transformer only has a 1:35 transformation ratio.
Therefore at least two of them would be required per panel.
This would be quite costly but should work well.
There may be some cheaper alternatives as prices for one from Plitron are way to expensive and about the cost of 4 of the Hammonds.

You could also just use a large stack of power toroidal transformers just the same.
I was able to get to the 15hz to 30hz range by stacking up 4 of my 200 watt transformers using a custom wound primary made out of speaker wire.
This worked great but the problem I had was that my cores have a lot of extra windings and this added capacitance but it was still usable to about 5khz to 8khz or so.
My plan is to strip off the extra winding's when I do my next build.

It takes a lot of iron to get down to the 20hz range and still get a good square wave out of it.
A square wave test will show a better results of its bandwidth capability than a sine wave will.
Using a sine wave to test at the 15hz to 30hz range showed that the more iron I used the cleaner the waveform got.
Most all of this is documented in this very long thread and covers just about everything you needed to know about step-up transformers and their design,

Step-up transformer design

Here is my double stacked cores,

Step-up transformer design

And my quad stacked cores,

Step-up transformer design

If you have the patients a very viable alternative is to to get a very large core from Alphacore and wind your own transformer.
For about the cost of just one of those Hammond's or less you can build a transformer with a much much more capability and performance than you would get using two or even four of those Hammond transformers.

Alpha-Core - Standard and Custom Cores from grain oriented silicon steel

Silicon Steel Toroidal Cores - In Stock

I would say that cores PN#120 to PN#160 is a good place to start preferably the largest core you can afford.
They also have winding service but I never inquired as to how much they charge.

You could have them wind a pair of none Bifilar 120v or 240v windings on it, again preferably the latter 240v or how ever many turns they can fit on it in a single layer with some 30 or 32 gauge wire (as a suggestion) and add your own primary turns as I did in my stacked core experiment.

If you choose for them to wind it, Ask them to use an extra thick layer of insulation on the core as this will help to reduce the transformers residual self capacitance.

Having a larger core also is a benefit of the extra area to fit the very large secondary winding's without having too resort to multi-layer winding's too much.
If they do have to use two or more layers, again, have them use a thickest insulation layer that they can achieve

Then you would have a very nice full range transformer.

I was going to go this route but funds are low and I gave up on the idea of full range panels for now.
I also have a few idea's for a direct drive method that I am going to invest and experiment with, based on my variable supply.
As well as after two years, I am still not working right now, so this does put a damper on things a bit.


Jer

Last edited by geraldfryjr; 18th August 2012 at 01:52 AM.
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Old 18th August 2012, 10:43 AM   #3
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I'm using a pair of custom wound transformers from a local transformer maker. The design is by one of the transformer gurus here. The ratio is around 1:90. I run my panels full range and I just love them. I can PM you the contact info, but the shipping cost is going to be quite a burden for you as the transformers are very big and heavy and I live in Southeast Asia.

Wachara C.
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Old 19th August 2012, 01:16 AM   #4
fperra is offline fperra  United States
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Quote:
Originally Posted by chinsettawong View Post
I'm using a pair of custom wound transformers from a local transformer maker. The design is by one of the transformer gurus here. The ratio is around 1:90. I run my panels full range and I just love them. I can PM you the contact info, but the shipping cost is going to be quite a burden for you as the transformers are very big and heavy and I live in Southeast Asia.

Wachara C.
Thanks for the offer Wachara, but I think I'll go ahead and give these Hammond transformers a try. I'll use 2 in parallel/series per speaker. If this doesn't work I guess I'll end up winding my own. The Oil burner transformers just don't have enough high frequency response.
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