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Old 11th April 2013, 04:19 PM   #41
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Location: Jackson,michigan
When you say "Stock EI cores" you must take into consideration the quality of the iron being used back then.

Your typical EI iron that was used for power transformers was not the same as what was typically used for Audio transfomers of decent quality.

Today these better types of iron are more commonly available and used more often than not because they make the transformer more efficient as efficiency is the name of the game these days.

Very good Points Bolserst!!
Lately I have been think about using bridged amps with lower transformation ratio in order to get that higher voltage swing that is needed while not having to dip very far below the 4 ohm range.

It makes little difference on how much power is actually used as it is nearly the same only the impedance is shifted.
I found that I can get 40Vms at a 300Hz saturation point.

At 40Vrms I get 4500Vp-p out of the AS-1206(m) and this actually enough to make my little panel really sing.
With a bridge amp this would be pushing the voltage levels near past the capabilities that the panel was designed for.
Basically were I had left off when it burned up, only I use using a 1:256 ratio and less than a 20Vrms input.
Since the panel was naturally crossed over at 600Hz or so this makes 80V quite a feasible voltage limit using just one core without demanding an incredible amount of current from the amplifier.

Next on my list is to Build a PA200 chipamp inorder to handle the low impedance dips and see how it will perform.
At only 20Vrms this is still 28Vpeak and is more than what I was using, when I left off.

Then I will build a bridged version in order to double up the voltage and see if I can get away with using just the one AS-1206 core.
I am also hoping that this will work using my PE cores with the 10 turn winding at 1:64 ratio or somewhere in between with a 15 turn at 1:42.6 ratio or so.
Of course running at a lower level will help to extend my lowest crossover point.

With the little panels at 105db it takes everything the little 5.25" woofer can muster up to compete against them anyhow.
All that is required to exceed this is 20Vpeak at 1:256 or 5Kv peak with a 7Kv Bias voltage.

I will build a larger panel soon that I can compare the differences myself and see how it pans out.

jer

Last edited by geraldfryjr; 11th April 2013 at 04:24 PM.
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Old 11th April 2013, 04:43 PM   #42
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Quote:
Originally Posted by tyu View Post
An Dont take what i am saying the roungway....It know ones place to tell me are anyone what for them to use...your all doing great work for all to see...
For years all i have heard..An read....is the Acoustat stepup tranfourmers were junk!
An we can get better sound on the Acoustat panels with better iorn...
An the ML Tranfourmer are low cost junk..an we can do better...
An i have had the Simmit here an the setup troi Tranfourmer in the Over $10k looks just like 1 size wize the Antek...an some say these are great sounding speakers...

Funny thing is i have had SoundLab,Acoustats,ML, Quad,KLH,JanZen,ESL an with work thay all sound great with stock EI cores ....I like all i gess just wont better.....thanks for all your time...
At least Quad uses c-cores (esl-57 and esl-63 )
A costum made esl transformer cost about 100-200 so still a fraction of all the other costs.
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Old 6th January 2014, 01:32 PM   #43
Tenson is offline Tenson  United Kingdom
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Hi chaps,

I have tested 3 transformers and here are the results. All are pretty similar.

The transformers all had 2x 6V windings connected in parallel and used for the input. Then 2x 115V windings connected in series and used for the output.

I fed 10V input and got near 350V output.

I connected an attenuator at the output of the TX to feed my soundcard. This was 10Meg in series and 1Meg in parallel.

All impedance measurements were made without the attenuator connected, except this first one which shows both.

Block RK63/6

Click the image to open in full size.

Click the image to open in full size.

Nuvotem 91227-P2S2

Click the image to open in full size.

Click the image to open in full size.

Noratel TA030/06 (Ordered Multicomp but got this)

Click the image to open in full size.

Click the image to open in full size.

The reason the impedance plots look jagged is because I was feeding it directly from the headphone output of my soundcard. It's probably drawing too much current, but IME the plots are pretty accurate.

I noticed that all distortion plots looked similar, and the top end impedance is very low, so I also tried each with a 1.2R resistor in series with the input.

Block

Click the image to open in full size.

Nuvotem

Click the image to open in full size.

Noratel

Click the image to open in full size.

I thought this would improve distortion in general, but while HF distortion does seem to reduce, interestingly 2nd harmonic seems to increase in the lower range.

Finally, I tired the Block and Noratel with the outputs in series to give twice the step-up. I tested this with 5V input and about 350V output.

Block and Noratel in Series (no series resistor at input)

Click the image to open in full size.

Last edited by Tenson; 6th January 2014 at 01:35 PM.
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Old 6th January 2014, 01:38 PM   #44
Tenson is offline Tenson  United Kingdom
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So, any comments?

I can see the effect of the winding capacitance causing the HF to go up a little and the impedance to drop. Adding the series resistor smooths the FR and increases the impedance slightly but makes 2nd harmonic higher in the mid-range. Why?

What have I learned? Well I think the amp having a hard time driving the impedance is probably the main cause of distortion rather than the TX itself, especially at HF.

It makes me think okay that was much better than expected from a mains TX, but perhaps I should try a valve amp output TX next.

My plan is to run a panel from about 300Hz up to 10KHz, so these could be suitable but if I can get better that would be nice.
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Old 6th January 2014, 02:02 PM   #45
Bazukaz is offline Bazukaz  Lithuania
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Hi,

Take a look to this page(especially fig. 11.5) :
Transformers Part 2 - Beginners' Guide to Electronics

As you can see both Lp(primary inducatance) which is non-linear as well as Rp(iron loss) components are in parallel with load. That means if Ll(leakage inductance) and Rw(series resistance) were zero Lp & Rp would have no effect on distortion.
By increasing Rw both non-linearity of core inductance as well as iron losses cause the voltage to fluctuate at load more, causing increased distortion.

Regards,
Lukas.


Quote:
Originally Posted by Tenson View Post
So, any comments?
I can see the effect of the winding capacitance causing the HF to go up a little and the impedance to drop. Adding the series resistor smooths the FR and increases the impedance slightly but makes 2nd harmonic higher in the mid-range. Why?
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Old 6th January 2014, 02:14 PM   #46
Tenson is offline Tenson  United Kingdom
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Thanks Lukas that makes more sense now.

Actually I had meant to post this all in the thread Toroidal Transformers for ESL Panels would a mod kindly move it over there? It makes more sense for people searching later.
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Old 6th January 2014, 06:25 PM   #47
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Very Good !!!

I many of my tests I have found the same jagged irregularity in some of the curves and found them to be random and intermittent.
I had found this to be the fault of my motherboards sound card.
My good out board sound cards don't do that and produce clean curves.

You can do a Loop back test to verify this.

I was pretty much stuck using my motherboard sounds at the time.
But here are a few examples of the same issues I had as well.

The other thing is that if you don't use a buffer in between the divider and the sound card input you will get non-linearity's as as the low impedance of the capacitor input of the sound card input changes and is not driven with enough current from the output of your high impedance voltage divider.

Else your curves look pretty good.
Very similar to my first curves then I found the issue I had explained using Visual Analyzer and made a buffer and now they are clean and accurate.

Exploring Visual Analyser (VA)

Be sure that you use an opamp the is unity gain stable if you use a unity gain buffer.
I had found the sometimes the opamp I was using would set it self into oscillation and it took me a while to find this as it didn't happen all of the time.

The photo of the Holm sweep may have been from using my GINA24 card in my other machine and it is very clean.
I will see if I still have the plots I did using the other cards.
I was having a hard time trying to figure out if it was the sound card or the software that was causing the glitches.

In my earlier post using SimpleS I had the same issues and they went away when I switched to a better sound card in a different machine and is why the curves were smooth and doing the same test with the same Transformer on my new motherboard's sound system and produced dirty curves again.

Here is the thread were I described the weird issues I was having too,

A TEST JIG FOR FINDING ESL STEP-UP TRANSFORMER PARAMETERS

The reason I was stuck was that my good sound cards (Phillips PSC706, Creative X-Fi and Gina24) don't work in my new machine with Win7.

What are the wattage ratings of your three samples, or, are their core sizes the same or different?

The First and last photos should be close to what your results should be with out all of the noise.

Cheers !!!

jer
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Old 6th January 2014, 06:49 PM   #48
Tenson is offline Tenson  United Kingdom
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I used an M-Audio FastTrack Ultra. In the distortion and FR tests this was feeding an Alesis RA500 amp (one channel not bridged) and back to the M-Audio line input via attenuator.

The impedance test was directly fed from the M-Audio.

I don't really follow your comment about the capacitor input of the soundcard? Why will it help to have a buffer, since the soundcard input is buffered already? I was getting near 1V into my soundcard.

I should add, I have used this card to do distortion tests before and it produces clean curves. Here is a loop-back of the soundcard (no power amp).

Click the image to open in full size.

Last edited by Tenson; 6th January 2014 at 06:56 PM.
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Old 6th January 2014, 10:20 PM   #49
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Most sound cards have a capacitor at the input.

The input impedance changes with frequency and as it is in parallel with the bottom resistor of the voltage divider with respect to ground.

Do a Loop back test with your amp connected to such a divider of say 10:1 or 20:1 or higher with the input to the sound card taken off of the divider and see how it compares to with signal coming right out of the amp without it.

Just be very careful that you don't go over the voltage input rating of your sound card, typically stay below 5Vp-p to be safe, YMMV.

You probably won't need to do the test without it, if, your amp is of good quality and has a flat response.

This is how I had discovered this, as I wanted to do a loop back reference and found the FR had changed from measuring directly out of the amp itself compared to using the voltage divider knowing that my amp is fairly flat.
Adding the buffer corrected this.

Your card may be different and may very well be going directly into an opamp, instead of going into a capacitor and then into an opamp.

A unity gain buffer has a very high input impedance at the + input of an opamp and doesn't impose any changing load on the bottom of the divider.

This was also an issue when I was using my DVM and I discovered that I was getting errorneous readings as the meters input impedance was much lower and in parallel with the bottom resistor thus changed the value of my Calculated Division Ratio when I started measuring high voltages while I was designing my Variable HV Bias supply.

The output(High) impedance of the divider needs to feed an even higher input impedance, a unity gain buffer (current gain) is able to have enough current to properly feed the low impedance input of the sound card without having any voltage droop of the signal you are trying to measure and/or without loading the divider changing the division ratio.

A capacitors resistance gets lower as the frequency get higher.

This calculator may be able to help you as it also includes the input resistance a the measuring circuit,

Voltage Divider

jer
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Old 7th January 2014, 11:36 AM   #50
Tenson is offline Tenson  United Kingdom
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Oh, now I get you! I had thought you are talking about the DC blocking cap but you mean the RF filter cap usually about 200pF. Also yes, of course the output of the voltage divider is about 1Meg so it will not feed the 10K input of my soundcard well. Can't believe I didn't think of that, usually I use a much lower value voltage divider for recording the output of amps, like 1K output Z.

I shall build a high-Z buffer and try again!
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